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Photoreceptor Anatomy and Function

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379 Questions

In what part of the retina are photoreceptors located?

Outer retina

What is the primary function of photoreceptors in the retina?

To convert light energy into electrical energy

What is the term for the constant release of the excitatory neurotransmitter glutamate in the dark?

Dark current

What is the primary mechanism by which rods maintain their resting potential in the dark?

Na+/K+ ATPases in the inner segment

What is the result of the phototransduction cascade in rod activation?

Hyperpolarization of the photoreceptor membrane

What is the first step in the phototransduction cascade?

Light photon activates rhodopsin

What is the result of the activation of phosphodiesterase (PDE) in the phototransduction cascade?

Conversion of cGMP to GMP

What is the purpose of Na+/K+ ATPases in the inner segment of photoreceptors?

To maintain the resting potential of rods

What is the effect of hyperpolarization of the photoreceptor membrane?

Decreased release of glutamate

What is the function of guanylate cyclase activating protein in the phototransduction cascade?

To increase the concentration of cGMP in the photoreceptor cells

Which type of bipolar cells synapse with ON ganglion cells in the IPL sublamina b?

ON bipolar cells

Which subtype of ganglion cells is sensitive to low contrast and movement?

Parasol ganglion cells

What is the primary function of horizontal cells in the retina?

Lateral inhibition and signal modulation

Which layer of the retina contains the cell bodies of horizontal cells?

Inner nuclear layer

What is the primary function of amacrine cells in the retina?

Modulation of neurotransmitter release

Which subtype of ganglion cells is involved in the perception of color and fine detail?

Midget ganglion cells

What is the pathway involved in the transmission of S cone signals?

Bistratified pathway

Which type of bipolar cells do not contact ganglion cells?

Rod bipolar cells

What type of receptor is primarily responsible for the transmission of signals from photoreceptors to ON bipolar cells?

Metabotropic glutamate receptor 6 (mGluR6)

In which layer of the retina do the synapses between photoreceptors and bipolar cells occur?

Outer plexiform layer

What is the effect of light on the activity of cone OFF bipolar cells?

They become inactive and hyperpolarize

What type of synapse is characteristic of the photoreceptor/bipolar cell synapse?

Ribbon synapse

What is the primary effect of glutamate on ON bipolar cells in the dark?

Hyperpolarization and inactivation

What is the primary difference between the receptor types found on cone ON and cone OFF bipolar cells?

Cone ON bipolar cells have metabotropic receptors, while cone OFF bipolar cells have ionotropic receptors

What is the effect of light on the activity of ON bipolar cells?

They become active and depolarize

Which of the following bipolar cell subtypes synapse with OFF ganglion cells in the IPL sublamina a?

OFF bipolar cells

What is the primary function of the S cone pathway in the retina?

Proprioception in the IPL

What is the characteristic of the synapse between rod bipolar cells and ganglion cells?

No synapse with ganglion cells

Which subtype of ganglion cells projects to the superior colliculus?

Photosensitive ganglion cells

What is the primary characteristic of the midget ganglion cells?

Smaller receptive field

Which type of cell is an interneuron in the lateral pathway?

Horizontal cells

What is the primary function of the parvocellular layers in the LGN?

Perception of color and fine detail

Which subtype of ganglion cells is involved in the perception of low contrast and movement?

Parasol ganglion cells

What is the primary receptor type responsible for signal transmission from photoreceptors to cone OFF bipolar cells?

Ionotropic glutamate receptor types (AMPA, kainate)

What is the effect of glutamate on cone OFF bipolar cells in the light?

They become inactive and hyperpolarize

Which type of synapse is characteristic of the photoreceptor/bipolar cell synapse in the outer plexiform layer?

Ribbon synapse

What is the primary function of horizontal cells in the retina?

To modulate the activity of photoreceptors and bipolar cells

What is the primary difference between the receptor types found on cone ON and cone OFF bipolar cells?

Metabotropic vs. ionotropic

What is the effect of light on the activity of ON bipolar cells?

They become active and depolarize

Which type of bipolar cells synapse with ganglion cells in the inner plexiform layer?

Both ON and OFF bipolar cells

What is a characteristic of organisms that can oxygenate their cells using diffusion alone?

They have a low oxygen requirement

What is the primary function of blood in the human body?

To transport oxygen and nutrients to cells and remove waste products

What percentage of blood volume is comprised of red blood cells?

45%

Why do humans need a circulatory system?

Because we have a high oxygen requirement

What is a key difference between organisms that use diffusion for oxygenation and humans?

The level of oxygen requirement

What percentage of blood in the body is contained in veins?

Most of the blood in the body

What is the primary function of valves in veins?

To assist unidirectional blood flow to the heart

What is the velocity of blood flow in aorta?

30 cm/sec

What is the primary function of the intima in arteries?

To provide a smooth surface for blood flow

What type of arteries have a reduced medial thickness and contain elastin and collagen?

Distributing arteries

What is the purpose of elastin in arteries?

To dampen pulse waves

What is the term for the peak pressure in the arterial pulse wave?

Systolic pressure

What is the primary function of capillaries?

To facilitate gas and metabolite exchange

What is the characteristic of arterioles?

Thin media and involved in setting peripheral resistance

What is the primary characteristic of laminar flow in capillaries?

Smooth flow

What is the primary function of venules?

To merge and form veins

What is the term for the drop in pressure just before the next pulse in the arterial pulse wave?

Dicrotic notch

What is the characteristic of elastic arteries?

Thick walls to withstand high pressure

What is the term for the normal blood pressure?

Normal systolic pressure

What is the primary function of the media in arteries?

To regulate blood pressure

What is the primary component of the artery wall that thickens with increase in size?

Adventitia

What is the characteristic of capillaries?

Single endothelial layer

What is the main function of the intima in arteries?

To provide a smooth surface for blood flow

Which type of arteries have a large diameter and thick walls?

Elastic arteries

What percentage of blood in the body is contained in veins?

most of the blood in the body

What is the primary function of valves in veins?

To assist in unidirectional blood flow to the heart

What is the primary function of arterioles?

To increase peripheral resistance

What is the site of gas and metabolite exchange in the circulatory system?

Capillaries

What is the velocity of blood flow in the aorta?

30 cm/sec

What is the primary function of the intima in arteries?

To provide a smooth surface for blood flow

Which of the following blood vessels is characterized by a single endothelial layer surrounded by a basement membrane?

Capillaries

What is the primary function of elastin in arteries?

To dampen pulse waves

What is the primary function of venules?

To merge and form larger veins

Which layer of an artery is composed of connective tissue?

Adventitia

What is the characteristic of blood flow in capillaries?

Laminar flow

What is the result of the heart pumping from the left ventricle?

An increase in pressure

What is the primary function of elastic arteries?

To buffer pulse pressure

What is the primary function of the adventitia in veins?

To provide structural support

What is the velocity of blood flow in capillaries?

0.3 mm/sec

What is the primary function of the lymphatic system?

To maintain fluid homeostasis and immune function

What is the main difference between initial and collecting lymphatics?

Collecting lymphatics have a continuous basement membrane, while initial lymphatics do not

What is the role of the vascular component in bone marrow?

To provide a microenvironment for T cell maturation in the absence of the thymus

What percentage of immune cells in bone marrow are CD4+ T cells?

2-2.5%

What is the role of lymphatic vessels in fluid homeostasis?

To return interstitial fluids to the circulation

What is the primary function of the haematopoietic component in bone marrow?

To produce hematopoietic stem cells

What is the role of the lymphatic system in immune function?

To provide a site for immune cell activation and proliferation

What is the percentage of immune cells in bone marrow that are plasma cells?

0.5-1%

What is the primary function of mesenchymal stem cells in bone marrow?

To differentiate into mesenchymal tissue

What is the role of protein fibrillin in lymphatic vessels?

To anchor endothelial cells to the extracellular matrix

What is the primary function of the red pulp in the spleen?

To filter old red blood cells, antigens, and microorganisms

What is the name of the vessel that contains lymphatic vessels in the eye?

Schlemm's canal

What is the name of the marker that is specific to lymphatic endothelial cells?

LYVE-1

What is the name of the disorder that can induce lymphangiogenesis in the cornea?

Dry eye

What is the name of the vessel that drains the eyelids?

Conjunctival lymphatic vessel

What is the name of the cells that are involved in the immune response to blood-borne pathogens?

T cells

What is the name of the structure that filters lymph?

Lymph nodes

What is the name of the condition that is characterized by the growth of lymphatic vessels in the cornea?

Lymphangiogenesis

What is the name of the vessel that contains blood vessels and lymphatic vessels in the eye?

Ciliary body

What is the name of the tumor that can occur in the eye?

Lymphoma

What is the primary function of the lymphatic system with respect to fluid homeostasis?

To return interstitial fluids back to circulation

What is the main difference between initial and collecting lymphatics?

Initial lymphatics have a continuous basement membrane, while collecting lymphatics do not

What is the primary function of the haematopoietic component of the bone marrow?

To produce haematopoietic stem cells and haematopoietic progenitor cells

What percentage of immune cells in the bone marrow are CD4+ T cells?

1.5%

What is the primary function of the lymphatic system in the immune system?

To filter out pathogens and toxins

What is the primary function of mesenchymal stem cells in the bone marrow?

To differentiate into mesenchymal tissue

What is the percentage of myeloid-derived suppressor cells in the bone marrow?

20-30%

What is the primary function of the vascular component of the bone marrow?

To provide a microenvironment for haematopoiesis

What is the primary function of regulatory T cells in the bone marrow?

To suppress immune responses

What percentage of immune cells in the bone marrow are natural killer T cells?

0.4-4%

What is the primary function of the red pulp in the spleen?

To filter old red blood cells, antigens, and microorganisms

What is the primary function of the white pulp in the spleen?

To provide an immune response to blood-borne pathogens

What is the role of LYVE-1 in the eye?

A marker for lymphatic vessels

What is the function of the lymphatic system in the eye?

To maintain fluid homeostasis and provide immunity

What is the result of chronic dry eyes in the cornea?

Increased lymphangiogenesis

What is the role of VEGFR-2 in the corneal epithelial cells?

To suppress lymphatic growth

What is the function of the lymphatic vessels in the eyelids?

To drain into the bloodstream

What is the characteristic of lymphatic vessels in the choroid?

They have a net-like structure with a pseudo-vessel appearance

What is the implication of lymphoma in the eye?

It can be localized or systemic

What is the importance of the lymphatic system in the eye?

It is critical to fluid homeostasis and immunity

The lymphatic system helps to maintain ______ by returning interstitial fluids back to circulation.

fluid homeostasis

Initial lymphatics have a ______ of endothelial cells, whereas collecting lymphatics have a continuous basement membrane.

monolayer

The ______ component of bone marrow provides a microenvironment for T cell maturation in the absence of thymus.

vascular

CD4+ T cells make up approximately ______ % of immune cells in bone marrow.

1.5

The lymphatic system plays a crucial role in the ______ system, helping to defend against infection and disease.

immune

Lymphatic vessels can be classified into two types: ______ lymphatics and collecting lymphatics.

initial

The haematopoietic component of bone marrow contains ______ stem cells and progenitor cells.

haematopoietic

Regulatory T cells make up approximately ______ % of immune cells in bone marrow.

0.5

The lymphatic system helps to collect and return ______ fluids back to the circulation.

interstitial

Collecting lymphatics have a surrounding ______ membrane, which is not present in initial lymphatics.

basement

The _______________ is responsible for maturation of T cells from bone marrow.

thymus

The spleen consists of _______________ and white pulp.

red

Tonsils and adenoids trap _______________ in the nasal and oral passage.

pathogens

Lymph nodes filter _______________ and store and transport B and T cells.

lymph

Lymphatic vessels in the eye were previously thought to be only present in the _______________.

conjunctiva

Corneal epithelial cells secrete _______________ to suppress lymph growth.

VEGFR-2

The _______________ canal is involved in the drainage of lymph in the eye.

Schlemm's

Dry eyes can induce _______________ in the cornea.

lymphangiogenesis

Lymphoma is a type of _______________ tumor that can be localized or systemic.

ocular

The lymphatic system is critical for _______________ homeostasis and immunity.

fluid

The kidney is ______ shaped.

bean

The ______ is the functional unit of the kidney.

nephron

The glomerular filtration barrier has three layers: endothelium, basement membranes, and ______.

epithelium

The ______ is the central region of the kidney.

medulla

The papilla is the ______ region of the kidney.

drainage

Fluid homeostasis involves the reabsorption of ______.

sodium

The kidney regulates ______ homeostasis.

electrolyte

The kidney also regulates ______ pH.

blood

Waste ______ is an important function of the kidney.

clearance

The ______ is the outer region of the kidney.

cortex

The _______________ produces hormones including renin, erythropoietin and Vit D.

kidney

Diabetes is characterized by high levels of _______________ in the blood.

glucose

The liver receives 75% of its blood flow from the _______________ vein.

portal

The functional unit of the liver is the _______________ lobule.

liver

Hepatocytes make up approximately _______________ of liver cells.

80%

Liver sinusoidal endothelial cells form a _______________ barrier between blood cells and hepatocytes.

permeable

The liver stores glucose as _______________.

glycogen

Jaundice is caused by a buildup of _______________ in the skin and conjunctiva.

bilirubin

The liver has two phases of _______________ for drug metabolism.

drug

The liver produces _______________, which helps increase lipid absorption from digestion.

bile

What is the functional unit of the kidney?

Nephron

What is the outer region of the kidney?

Cortex

What is the function of the glomerular filtration barrier?

To filter large molecules

What is the purpose of the epithelium in the glomerular filtration barrier?

To form the filtration slits

What is the primary mechanism of fluid homeostasis in the kidney?

Reabsorption of sodium

What is the purpose of the basement membrane in the glomerular filtration barrier?

To filter large molecules

What is the function of the kidney in electrolyte homeostasis?

To reabsorb sodium

What is the function of the papilla in the kidney?

To drain the kidney

What is the function of the glomerulus in the kidney?

To filter large molecules

What is the purpose of the endothelium in the glomerular filtration barrier?

To filter large molecules

What is the primary function of Kupffer cells in the liver?

Immune sentinels

What is the result of uncontrolled type I diabetes?

Increased blood sugar levels

What is the primary function of the liver lobule?

Functional unit of the liver

What is the result of jaundice in adults?

All of the above

What is the primary function of hepatocytes?

Basic liver function

What is the role of the hepatic stellate cells?

Vitamin A and lipid storage

What is the primary mechanism of drug metabolism in the liver?

Phase I: Oxidation, Phase II: Conjugation

What is the function of the liver in glucose metabolism?

All of the above

What is the result of diabetic retinopathy?

Damage to blood vessels

What is the primary function of the liver sinusoidal endothelial cells?

Permeable barrier between blood cells and hepatocytes

What is the average lifespan of an ATP molecule?

1-5 minutes

What is the primary function of the exocrine pancreas?

Producing enzymes to help with food digestion

What is the outcome of high glucose levels on pancreatic beta cells?

Increased insulin secretion

What is the primary function of insulin in glucose homeostasis?

Decrease blood glucose levels

What is the characteristic of Type 1 Diabetes Mellitus?

Destruction of beta cells

What is the primary function of glucagon in glucose homeostasis?

Increase blood glucose levels

What is the outcome of low glucose levels on pancreatic alpha cells?

Increased glucagon secretion

What is the primary function of the endocrine pancreas?

Producing hormones such as insulin and glucagon

What is the primary characteristic of Gestational Diabetes Mellitus?

Pregnancy-related and glucose intolerance

What is the primary treatment for Type 1 Diabetes Mellitus?

Insulin injection

What is the primary source of ATP molecule in the human body, and how many times is it recycled daily?

Glucose, proteins, and lipids; ~300 times

What is the role of insulin in glucose homeostasis, and which organ produces it?

Insulin decreases blood glucose level; pancreas

What is the difference between exocrine and endocrine functions of the pancreas?

Exocrine: produces enzymes for digestion; endocrine: produces hormones like insulin and glucagon

What is the mechanism of glucose-stimulated insulin secretion in pancreatic beta cells?

High glucose → increased ATP → closure of KATP channels → Ca2+ entry → insulin exocytosis

What is the primary function of glucagon, and how does it regulate blood glucose levels?

Glucagon increases blood glucose levels; stimulates endogenous glucose production

What are the three main types of diabetes mellitus, and what are their characteristics?

Type 1: juvenile, insulin-dependent; Type 2: mature, non-insulin-dependent; Gestational: during pregnancy

What is the primary treatment for Type 1 diabetes, and what are the risks of overtreatment?

Insulin injection; hypoglycaemic shock, dizziness, sweating, tachycardia, and coma

What is the mechanism of insulin secretion in response to high glucose levels in pancreatic beta cells?

High glucose → increased ATP → closure of KATP channels → Ca2+ entry → insulin exocytosis

What is the role of the liver in glucose homeostasis, and how does it regulate blood glucose levels?

Stores glucose as glycogen; regulates blood glucose levels through glycogenolysis and gluconeogenesis

What is the difference between the exocrine and endocrine functions of the pancreas, and how do they relate to glucose homeostasis?

Exocrine: produces enzymes for digestion; endocrine: produces hormones like insulin and glucagon; regulates glucose homeostasis

What is the main function of smooth muscle in the iris?

To control the amount of light entering the eye

What is the difference between visceral and multiunit smooth muscle?

Visceral smooth muscle contracts as a single unit, while multiunit smooth muscle contracts independently

What is the function of the myelin sheath in neurons?

To insulate and facilitate rapid transmission of electrical impulses

What is the role of astrocytes in the CNS?

To maintain blood-brain barrier and extracellular homeostasis

What is the visual pathway?

A collection of neurons from the retina to the brain

What is optic neuritis?

Inflammation of the optic nerve

What is the function of thyroid eye disease?

To cause inflammation and swelling in the eye

What is the role of interneurons in the CNS?

To establish networks between sensory and motor neurons

What is the function of oligodendrocytes in the CNS?

To myelinate axons

What is the role of microglia in the CNS?

To clear cell debris and dead neurons

What is the primary function of skeletal muscles?

To maintain body posture and movement of limbs and digits

What is the main characteristic of smooth muscle cells?

No striation, regulated by the autonomic nervous system

What is the function of perimysium in skeletal muscles?

To form a bundle of fibres

What is the characteristic of cardiac muscle cells?

Inherent rhythmicity and spontaneous contraction

What is the function of the endomysium in skeletal muscles?

To surround individual muscle fibres

What is the characteristic of red muscle fibres?

Small fibres with many mitochondria

What is the function of epimysium in skeletal muscles?

To surround a collection of fascicles

Which type of muscle fibre is responsible for fast twitch contraction?

White fibres

What is the function of myoglobin in muscle cells?

To store oxygen

What is the characteristic of muscle cells responsible for body movement and controlling the shape/size of internal organs?

Elongated shape, arranged in parallel array

What are the two types of epithelial cells, and what are their functions?

Surface epithelium (protection, absorption, and transcellular transport) and glandular epithelium (secretory functions, e.g. producing hormones, enzymes, and mucus)

What are the three main functions of epithelial cells?

Protection, secretory, and transcellular transport

What is the composition of epithelial cells, and what is the importance of the basement membrane?

Epithelial cells are composed of specialized junctions, apical surface, and basement membrane, which provides a selective barrier between epithelial cells and underlying connective tissues

What is the origin of surface epithelium, and what are some examples of surface epithelium?

Surface epithelium originates from ectoderm, mesoderm, and endoderm, and examples include epidermis, GI tract lining, and body cavity linings

What is the function of glandular epithelium, and what are some examples of glandular epithelium?

Glandular epithelium is responsible for secretory functions, such as producing hormones, enzymes, and mucus, and examples include pituitary gland and sweat glands

What is the importance of transcellular transport in epithelial cells, and what is an example of transcellular transport?

Transcellular transport is essential for the movement of molecules across epithelial layers, and an example is the transport of molecules across the intestinal epithelium

What is the characteristic of transitional epithelium that allows it to adapt to changes in tissue distention?

Cells can change shape

What are the two main categories of glands based on their secretion mechanism?

Exocrine and Endocrine

What type of connective tissue has a high proportion of fibres and little ground substance, providing maximal tensile strength?

Regular dense CT

What is the function of stromal cells in connective tissue?

Supporting the parenchyma

What type of gland produces the lipid layer of the tear film?

Meibomian gland

What is the main function of goblet cells in the digestive tract?

Secreting mucinogens

What are the two components of the basement membrane, and what are their functions?

The two components of the basement membrane are the thin matrix layer known as the basal lamina (lamina lucida and lamina densa) and the reticular layer with collagen fibrils. The basal lamina provides a scaffold for epithelial cells to attach, and the reticular layer provides mechanical strength and supports the epithelium.

What are the main functions of the basement membrane, and how does it regulate permeability?

The basement membrane physically binds the epithelium to the underlying tissue, controls epithelial growth and differentiation, and regulates permeability by acting as a selective barrier to the passage of molecules from one compartment to another.

What are the main components of the basement membrane, and how do they interact with each other?

The main components of the basement membrane are type IV collagen, laminin, nidogen/entactin, and fibronectin. Type IV collagen forms the structural framework, laminin provides a scaffold for collagen binding, and nidogen/entactin promotes the binding of laminin and collagen. Fibronectin binds to type III collagen and integrins.

What is the role of glycoproteins and proteoglycans in the basement membrane?

Glycoproteins such as laminin and fibronectin provide a scaffold for collagen binding and promote cell adhesion. Proteoglycans are bound to the laminin scaffolding and tether and accumulate growth factors in the basement membrane.

What are the three layers of the basement membrane, and what are their characteristics?

The three layers of the basement membrane are the lamina lucida, lamina densa, and lamina fibroreticularis. The lamina lucida is a thin, electron-lucent layer that adjoins the plasma membrane of basal epithelial cells. The lamina densa is a dense, intermediate layer. The lamina fibroreticularis is a broad layer that merges with the fibrous, reticular components of the underlying connective tissue.

What is the function of type IV collagen in the basement membrane?

Type IV collagen forms the structural framework of the basement membrane, providing mechanical strength and support to the epithelium.

What is the main function of simple epithelial cells with a cuboidal shape, and where are they typically found in the body?

Their main function is secretory/absorptive, and they are typically found in collecting tubules of the kidney, ducts draining exocrine glands, and under the anterior lens capsule.

What is the role of the basement membrane in regulating epithelial growth and differentiation?

The basement membrane regulates epithelial growth and differentiation by providing a scaffold for epithelial cell attachment and promoting cell signaling.

What is the characteristic of pseudostratified epithelial cells, and where are they typically found in the body?

The characteristic of pseudostratified epithelial cells is that they appear as if cells are not in contact with the basal lamina, but EM shows that all cells contact the basal lamina, and nuclei are at different levels. They are typically found in the upper respiratory tract and vas deferens.

What is the main function of stratified squamous epithelial cells, and where are they typically found in the body?

Their main function is protection to mechanical stress and desiccation, and they are typically found in skin, oesophagus, oral cavity, anal canal, uterine cervix, and vagina.

What is the characteristic of stratified columnar epithelial cells, and where are they typically found in the body?

The characteristic of stratified columnar epithelial cells is that cells in the apical layer are connected by gap junctions and desmosomes, forming an impermeable layer, and they are typically found in the eye conjunctiva and involved in mucus secretion.

What is the main function of stratified cuboidal epithelial cells, and where are they typically found in the body?

Their main function is secretion, and they are typically found in areas of the body that require secretion, such as glands.

What is the main difference between simple and stratified epithelial cells, and how are they classified?

The main difference between simple and stratified epithelial cells is the number of cell layers, with simple epithelial cells having one cell layer and stratified epithelial cells having multiple cell layers. They are classified based on the shape of the cells in the surface layer, with simple epithelial cells being classified as squamous, cuboidal, or columnar, and stratified epithelial cells being classified as squamous, cuboidal, or columnar.

What characterizes avascular epithelial tissue?

Specialized junctions and apical surface

What is the primary function of surface epithelium?

Protection and selective barrier function

Which type of epithelial tissue is composed of ectodermal, mesodermal, and endodermal origins?

Both surface and glandular epithelium

What is the primary function of glandular epithelium?

Secretion of hormones, enzymes, and mucus

What is the purpose of the basement membrane in epithelial tissue?

To separate the epithelial layer from underlying connective tissue

Which of the following is NOT a function of epithelial tissue?

Regulation of blood pressure

What is the primary function of the apical surface in epithelial tissue?

To facilitate transcellular transport

Which type of epithelial tissue is responsible for absorption in the gut?

Surface epithelium

What is the primary function of transcellular transport in epithelial tissue?

To transport molecules across the epithelial layer

Which of the following is a characteristic of glandular epithelium?

Secretes hormones and enzymes

What is the primary function of simple cuboidal epithelium?

Secretion and absorption

Which type of epithelium is found in the internal surface of the GI tract?

Simple columnar

What is the characteristic of pseudostratified epithelium?

Cells are in contact with the basal lamina

What is the main function of stratified squamous epithelium?

Protection against mechanical stress and desiccation

Where is simple endothelium found?

Lining the vascular system

What is the primary function of mesothelium?

Line the walls and covers of body cavities

Which type of epithelium is involved in secretion and absorption?

Simple cuboidal

What is the characteristic of simple columnar epithelium?

Cells are taller than they are wide

Which type of epithelium is involved in protection and secretion?

Stratified columnar

What is the primary function of stratified cuboidal epithelium?

Secretion

Which type of epithelial tissue is characterized by cells that can change shape depending on tissue distention?

Transitional epithelium

What is the primary function of serous glands?

To secrete an enzyme-rich watery fluid

Which type of connective tissue is characterized by a high proportion of fibers and little ground substance?

Dense connective tissue

What is the function of the stroma in an organ?

To support the parenchyma

What is the primary function of the basement membrane in regards to epithelial growth?

To control epithelial growth and differentiation

Which type of cell is a fixed, long-lived cell that is part of the resident population of connective tissue cells?

Fibroblast

What is the primary function of the parenchyma in an organ?

To perform the organ's specific function

Which of the following types of collagen is exclusively found in the basement membrane?

Type IV collagen

Which type of gland is characterized by the release of secretions into the bloodstream?

Endocrine gland

What is the function of glycoproteins in the basement membrane?

To form a scaffold for the binding of type IV collagen

What is the primary function of the extracellular matrix in connective tissue?

To provide mechanical strength

What is the primary function of the lamina lucida in the basement membrane?

To adjoin the plasma membrane of basal epithelial cells

Which of the following components of the basement membrane is responsible for tethering and accumulating growth factors?

Proteoglycans

Which type of epithelial tissue is characterized by the presence of invaginations of the surface epithelium?

Glandular epithelium

What is the primary function of the reticular layer in the basement membrane?

To merge with the fibrous, reticular components of the underlying connective tissue

What is the primary function of Meibomian glands?

To produce lipid layers of tear film

What is the term for the layer of the basement membrane that is composed of a thin matrix known as the basal lamina?

Lamina lucida

Which of the following components of the basement membrane is responsible for promoting the binding of laminin and type IV collagen?

Nidogen/entactin

What is the primary function of the basement membrane in regards to the epithelium?

To physically bind the epithelium to the underlying tissue

What is the term for the layer of the basement membrane that is a dense, intermediate layer?

Lamina densa

What is the process called when the sperm and egg unite to form a zygote?

Fertilisation

What is the term for the layers of cells that form during gastrulation?

Trilaminar mass of cells

Which of the following structures arises from the mesoderm?

Choroid

What is the term for the process by which the epiblast differentiates into the three germ layers?

Gastrulation

Which of the following structures arises from the surface ectoderm?

Lens

What is the term for the cavity that forms within the blastula?

Blastocoel

During which week of embryonic development does embryogenesis occur?

2-8 weeks

What is the term for the process by which the embryo undergoes rapid growth and development?

Embryogenesis

Which of the following structures arises from the neural crest?

Sclera

What is the term for the formation of the three germ layers during gastrulation?

Trilaminar mass of cells

What is the consequence of a RAX mutation during eye development?

Anophthalmia

During which week of eye development does the optic vesicle interact with the surface ectoderm to induce the lens placode?

Week 4

What is the term for the failure of the optic fissure to close during eye development?

Coloboma

During which week of eye development does the retina develop from the dorsal neuroectoderm of the optic vesicle?

Week 6

What is the term for the layer of cuboidal cells that forms the retinal pigment epithelium (RPE) during eye development?

Single layer of cuboidal cells

What is the purpose of the hyaloid artery during eye development?

To wrap around the posterior lens

What is the consequence of the failure of the optic fissure to close during eye development?

Formation of a coloboma

During which week of eye development do the retinal ganglion cell axons form the optic nerve fibers?

Week 6

What is the term for the process by which the lens vesicle forms during eye development?

Invagination

During which week of eye development does the choroidal vasculature form?

Week 7

What is the consequence of a RAX mutation during eye development?

Anophthalmia

During which week of development do the optic vesicles interact with the surface ectoderm to induce lens placode formation?

Week 4

What is the result of the invagination of the optic vesicle?

Formation of the inner layer of the optic cup (neural retina)

What is the term for the failure of the optic fissure to close?

Coloboma

During which week of development do the primary lens fibers form and obliterate the cavity within the lens vesicle?

Week 7

What is the purpose of the hyaloid artery during eye development?

To allow passage into the optic cup

What is the result of the proliferation of cells in the germinative zone of the inner layer of the optic cup?

Formation of retinal ganglion cell axons that enter the optic stalk

What is the critical period of eye development?

Week 4 to 8

What is the stage of embryonic development where the cells of the embryo undergo multiple rounds of mitotic cell division, and what is the name of the developing embryo at this stage?

The stage of embryonic development is cleavage, and the developing embryo is called a blastula.

Describe the formation of the bilaminar disc during embryogenesis, and its significance in embryonic development.

The bilaminar disc forms within the amniotic cavity during embryogenesis, and it gives the embryo its first orientation, establishing the dorsal (epiblast) - ventral (hypoblast) axis.

What are the three germ layers that arise from the proliferation and migration of epiblast during gastrulation, and what is the resulting structure?

The three germ layers are ectoderm, mesoderm, and endoderm, and the resulting structure is a trilaminar mass of cells called the gastrula.

Describe the contributions of the neural tube, neural crest, surface ectoderm, and mesenchyme to the development of the eye.

The neural tube forms the retina, epithelial linings of the iris and ciliary body, and the optic nerve. The neural crest forms the sclera, cornea, and choroid. The surface ectoderm forms the lens, corneal and conjunctival epithelium, and eyelids. The mesenchyme forms the choroid, sclera, corneal stroma, vitreous, and extraocular muscles.

Describe the formation of the optic vesicle during vertebrate eye development, and its significance in eye development.

The optic vesicle forms as a bilateral indentation soon after gastrulation, defined by the expression of eye field transcription factors. This is a critical stage in eye development, as it sets the stage for the formation of the eye and its components.

What is the significance of the 5-day post-fertilization stage in embryonic development, and what are the two distinct layers that form at this stage?

The 5-day post-fertilization stage is significant because it marks the formation of the blastocyst, consisting of an inner cell mass that will form the embryo and an outer layer of trophoblasts that will form the placenta.

Describe the subdivisions of the primitive gut that arise from the folding of the endoderm during embryogenesis, and their corresponding structures.

The subdivisions of the primitive gut are the foregut, midgut, and hindgut, which will give rise to the pharynx, lower respiratory tract, esophagus, stomach, duodenum, liver, pancreas, small intestine, and large intestine, respectively.

What is the number of bones in the human skull?

22

What is the name of the bone that forms the forehead?

Frontal

What is the name of the plane that divides the body into dorsal and ventral parts?

Coronal

What is the name of the bone that forms the cheekbone?

Zygomatic

What is the name of the anatomical term that means 'towards the nose'?

Nasal

What is the name of the cavity that contains the eye?

Orbit

What is the name of the bone that forms the lower jaw?

Mandible

What is the name of the plane that divides the body into superior and inferior parts?

Transverse

What is the name of the bone that forms the bridge of the nose?

Nasal

What is the name of the anatomical term that means 'away from the nose'?

Lateral

Which bone forms the lateral margin of the orbit?

Zygomatic bone

Which structure transmits the optic nerve and ophthalmic artery?

Optic canal

Which wall of the orbit is the thickest?

Lateral wall

Which of the following bones does not form part of the medial wall of the orbit?

Palatine bone

What is the primary function of the nasolacrimal duct?

To drain tears from the eye

Which of the following is a symptom of an orbital blowout fracture?

Bruising

Which of the following bones forms part of the floor of the orbit?

Maxillary bone

What is the primary function of the superior orbital fissure?

To transmit most of the other vascular and neural structures into the orbit

Which of the following bones forms part of the medial wall of the orbit?

Ethmoid bone

What is the primary function of the inferior orbital fissure?

To transmit the inferior ophthalmic vein and maxillary division of the trigeminal nerve

What is the name of the bone that forms the floor of the orbit and also contains the sphenoid sinus?

Sphenoid bone

What is the term for the plane that divides the body into superior and inferior parts?

Transverse plane

What is the name of the bone that forms the lateral wall of the orbit and also contains the lacrimal gland?

Zygomatic bone

What is the term for the direction that is towards the nose?

Nasal

What is the name of the bone that forms the lower jaw?

Mandible

What are the seven bones that form the orbit, and what is the purpose of these bones?

The seven bones that form the orbit are the frontal, sphenoid, zygomatic, maxillary, lacrimal, ethmoid, and palatine bones. These bones serve to protect the globe and provide a structural framework for the orbit.

Describe the composition and function of the orbital margin.

The orbital margin is composed of the frontal bone, zygomatic bone, and maxillary bone. The frontal bone forms the supraorbital margin, while the zygomatic bone and maxillary bone form the infraorbital margin. The orbital margin serves as the bony boundary of the orbit.

What are the main openings into the orbital cavity, and what structures pass through these openings?

The main openings into the orbital cavity are the optic canal, superior orbital fissure, and inferior orbital fissure. The optic canal transmits the optic nerve and ophthalmic artery, the superior orbital fissure transmits most of the other vascular and neural structures, and the inferior orbital fissure transmits the inferior ophthalmic vein and maxillary division of the trigeminal nerve.

What is an orbital/blowout fracture, and how is it diagnosed?

An orbital/blowout fracture is a type of fracture that occurs in the orbital bones, typically due to blunt trauma. It is diagnosed through a combination of clinical evaluation, imaging studies such as CT scans, and other diagnostic tests.

What is the function of the lacrimal system, and how does it relate to the nasal cavity?

The lacrimal system is responsible for producing and draining tears, which helps to lubricate and protect the eye. The lacrimal system is connected to the nasal cavity through the nasolacrimal duct, which allows for the drainage of excess tears into the nasal cavity.

What is the percentage of scleral dry weight comprised of collagen?

Around 90%

What is the term for the layer of tissue that attaches to the choroid by fine collagen fibres?

Lamina fusca

What type of cell synthesizes collagen, elastic, and reticular fibres?

Fibroblasts

What is the function of aggrecan in the sclera?

To sequester water within the scleral ECM

What is the term for the glycoprotein that possesses binding sites for collagen, fibrin, heparin, cell membranes, and various macromolecules?

Fibronectin

What is the composition of the scleral stroma?

Collagen, proteoglycans, and glycoproteins

What is the function of elastin in the sclera?

To form a meshwork of polypeptide chains

What is the percentage of scleral dry weight comprised of proteoglycans and glycosaminoglycans?

Around 1%

What is the term for the layer of tissue that is regarded as part of the choroid by some?

Lamina fusca

What is the term for the type of fibre that is formed by the assembly of staggered collagen molecules?

Fibril

What is the primary function of type III collagen in scleral fibrillogenesis?

To regulate fibril diameter

What is the characteristic of the organised bundles of fibrils in the sclera?

Irregularly arranged lamellae

What is the blood supply of the sclera?

Relatively avascular, apart from perforating vessels

What is the function of the episclera?

To provide nutritional and immunological support to the avascular sclera

What is the characteristic of the collagen bundles in the episclera?

Thinner and more loosely arranged than those in the sclera

What is the primary function of the anterior episcleral arterial circle?

To supply blood to the limbal, anterior conjunctival, and anterior episcleral tissues

What is the innervation of the sclera and episclera?

Shared innervation via long posterior ciliary nerves

What is the primary function of the episcleral collecting veins?

To drain blood and aqueous humour

What is the characteristic of the scleral fibrils?

Heterologous, with a range of diameters

What is the regional variation in scleral thickness?

Thickest in the posterior region and thinnest in the equatorial region

What is the Greek origin of the word 'sclera'?

Skleros

What is the function of the sclera in maintaining refractive stability?

It keeps the eye length stable during IOP and blood pressure changes

What is the purpose of the scleral canal and lamina cribrosa?

To sieve interwoven collagen fibrils

What is the dimension of the anterior scleral foramen externally?

11.6mm horizontal, 10.6mm vertical

What is the function of the sclera in relation to the ciliary muscle?

It opposes the contractile forces of the ciliary muscle

What is the percentage of scleral fibers that turn 90° to form the meninges?

2/3

What is the location of the posterior scleral foramen?

3mm medial to the vertical midline and 1mm below the horizontal meridian

What is the function of the sclera in relation to the extraocular muscles?

It provides stable anchorage for the extraocular muscles

What is the result of a 170μm change in axial length on refractive error?

A 0.50D change in refractive error

What is the composition of the sclera?

Dense, irregular connective tissue

Study Notes

Photoreceptors

  • Located in the outer retina and composed of cones and rods
  • No rods are found in the fovea
  • The periphery of the retina is dominated by rods
  • Photoreceptors convert light energy into electrical energy

Photoreceptor Anatomy

  • Spherule vs pedicle structure
  • Dark current is present when in the dark, maintaining the resting potential of rods
  • Depolarized at -40 mV, maintained by Na+/K+ ATPases in the inner segment
  • Constant release of the excitatory neurotransmitter glutamate

Rod Activation

  • Photons activate the phototransduction cascade
  • Closure of the cGMP-Na+ channels
  • K+ channels remain open
  • Hyperpolarization of the photoreceptor membrane (-70 mV)
  • Decrease in glutamate release

Phototransduction Cascade

  • Step 1: Light photon activates rhodopsin, converting it to metarhodopsin II
  • Step 2: Metarhodopsin II activates transducin, with GDP dissociating and GTP attaching
  • Step 3: The alpha-subunit GTP complex binds to both ends of the phosphodiesterase (PDE) molecule, activating PDE
  • Step 4: Activated PDE converts cGMP within the outer segment to GMP
  • Step 5: Decrease in cGMP within the outer segment, leading to closure of cGMP-dependent channels and subsequent decrease in dark current

Phototransduction Cascade Deactivation

  • Guanylate cyclase activating protein is involved in deactivation

Visual Cycle

  • ABCR: ATP binding cassette transporter
  • atRDH: all-trans retinol dehydrogenase
  • IRBP: interphotoreceptor retinoid binding protein
  • CRBP: cellular retinol binding protein
  • LRAT: lecithin retinol acyl transferase
  • RPE65: Retinal pigment epithelium-specific 65 kDa protein
  • 11cRDH: 11-cis retinol dehydrogenase

Rods vs Cones

  • Visual pigments: rods have rhodopsin, cones have S-cone/M-cone/L-cone (in humans)
  • Functional differences: rods are more sensitive to light, rods saturate in moderately bright light – non-functional during daytime, cones remain photosensitive even in bright light, and rods take longer to recover
  • Cone alternate recycling of all-trans-retinol

ON/OFF Channels

  • ON: depolarize (i.e., turn on) with light onset, hyperpolarize (i.e., turn off) with light offset
  • OFF: depolarize with light offset, hyperpolarize with light onset

Mammalian Retina

  • The retina consists of several types of cells, including photoreceptors, horizontal cells, bipolar cells, amacrine cells, and ganglion cells.

Photoreceptors and Synapses

  • Photoreceptors (rods and cones) transmit visual signals to bipolar cells through the outer plexiform layer.
  • The photoreceptor/bipolar cell synapse is a ribbon synapse.
  • Bipolar cells then transmit the signal to ganglion cells through the inner plexiform layer.

Bipolar Cells

  • There are two types of bipolar cells: ON bipolar cells and OFF bipolar cells.
  • ON bipolar cells have metabotropic glutamate receptor 6 (mGluR6) and are activated in the light and inactivated in the dark.
  • OFF bipolar cells have ionotropic glutamate receptor types (AMPA and kainate) and are activated in the dark and inactivated in the light.

Ganglion Cells

  • Ganglion cells are divided into ON and OFF types, which receive input from ON and OFF bipolar cells, respectively.
  • ON bipolar cells and ON ganglion cells synapse at the inner plexiform layer (IPL) sublamina b.
  • OFF bipolar cells and OFF ganglion cells synapse at the IPL sublamina a.
  • Rod bipolar cells do not contact ganglion cells.

Ganglion Cell Subtypes

  • There are several subtypes of ganglion cells, including:
    • Parasol cells: with larger receptive fields, input to magnocellular layers in the LGN, and detect low contrast and movement.
    • Midget cells: with smaller receptive fields, input to parvocellular layers in the LGN, and are involved in perception of color and fine detail.
    • Bistratified cells: with S cone pathway, proprioception, and IPL sublamina a.
    • Photosensitive cells: projecting to the superior colliculus.

Horizontal Cells

  • Horizontal cells are interneurons with dendrites in the outer plexiform layer and cell bodies in the inner nuclear layer.
  • They are involved in the lateral pathway.

Mammalian Retina

  • The retina consists of several types of cells, including photoreceptors, horizontal cells, bipolar cells, amacrine cells, and ganglion cells.

Photoreceptors and Synapses

  • Photoreceptors (rods and cones) transmit visual signals to bipolar cells through the outer plexiform layer.
  • The photoreceptor/bipolar cell synapse is a ribbon synapse.
  • Bipolar cells then transmit the signal to ganglion cells through the inner plexiform layer.

Bipolar Cells

  • There are two types of bipolar cells: ON bipolar cells and OFF bipolar cells.
  • ON bipolar cells have metabotropic glutamate receptor 6 (mGluR6) and are activated in the light and inactivated in the dark.
  • OFF bipolar cells have ionotropic glutamate receptor types (AMPA and kainate) and are activated in the dark and inactivated in the light.

Ganglion Cells

  • Ganglion cells are divided into ON and OFF types, which receive input from ON and OFF bipolar cells, respectively.
  • ON bipolar cells and ON ganglion cells synapse at the inner plexiform layer (IPL) sublamina b.
  • OFF bipolar cells and OFF ganglion cells synapse at the IPL sublamina a.
  • Rod bipolar cells do not contact ganglion cells.

Ganglion Cell Subtypes

  • There are several subtypes of ganglion cells, including:
    • Parasol cells: with larger receptive fields, input to magnocellular layers in the LGN, and detect low contrast and movement.
    • Midget cells: with smaller receptive fields, input to parvocellular layers in the LGN, and are involved in perception of color and fine detail.
    • Bistratified cells: with S cone pathway, proprioception, and IPL sublamina a.
    • Photosensitive cells: projecting to the superior colliculus.

Horizontal Cells

  • Horizontal cells are interneurons with dendrites in the outer plexiform layer and cell bodies in the inner nuclear layer.
  • They are involved in the lateral pathway.

Objectives and Introduction

  • The objectives of the topic include blood overview, heart anatomy, lung anatomy, and cardiopulmonary system and the eye
  • Blood is necessary for humans because it transports oxygen and carbon dioxide

Why Blood is Necessary

  • Some organisms can oxygenate their cells through diffusion alone, but this requires a moist epithelial surface and low oxygen requirement
  • Examples of organisms that use diffusion for oxygenation include jellyfish and sponges
  • Some organisms, such as frogs, supplement their circulatory system with diffusion
  • In humans, blood is necessary for transporting oxygen and carbon dioxide

What is Blood?

  • Blood is a mixture of cellular and acellular fractions that transport nutrients and remove waste products
  • The two main components of blood are cells and acellular fractions
  • There are two main types of cells in blood: Red Blood Cells and White Blood Cells
  • Red Blood Cells make up approximately 45% of blood volume

Blood Vessels

  • Arteries receive blood from the heart and need to withstand high pressure, high flow, and high shear.
  • Arteries have three tunics: intima, media, and adventitia.
  • Intima consists of endothelium monolayer and internal elastic lamina, comprised of connective tissue (elastin).
  • Media consists of smooth muscle, elastin, collagen, and external elastic lamina.
  • Adventitia consists of connective tissue (collagen and elastin).

Artery Types

  • Arteries branch (bifurcate) as they reduce in size.
  • Elastic (conduit) arteries have large, very thick walls, elastin to buffer pulse, and collagen for strength (e.g., aorta, ~10mm diameter).
  • Distributing (muscular) arteries have reduced medial thickness, contain elastin and collagen, and are involved in blood pressure regulation (e.g., carotid artery, 1-5 mm diameter).
  • Arterioles (resistance arteries) have thin media and are involved in setting peripheral resistance (e.g., central retinal artery, ~200 µm).

Capillaries

  • Capillaries are the smallest vessels (5-10 µm) with a single endothelial layer surrounded by a basement membrane.
  • They are the site of gas and metabolite exchange.
  • They represent the anastamosis between arterial and venous circulation.
  • Capillaries can be continuous, fenestrated, or sinusoid (levels of leakiness).

Venules

  • Venules are the smallest veins (5-15 µm) immediately downstream from capillaries.
  • They have intima, very thin media, and adventitia.
  • Venules are porous and fragile.
  • They merge/coalesce to form veins (e.g., central retinal venule).

Veins

  • Veins contain most of the blood in the body.
  • They have lower blood pressure than arteries.
  • They contain intima, thin media, and adventitia.
  • Adventitia thickens with increase in size.
  • Valves assist unidirectional blood flow to the heart.

Blood Flow

  • In the aorta, blood travels at 30 cm/sec.
  • In capillaries, blood travels at 0.3 mm/sec.
  • Slowed flow due to overall diameter in all capillaries >> aorta.
  • Laminar (smooth) flow is required in the capillary bed.
  • Elastin in the arteries dampens pulse waves.

The Arterial Pulse Wave

  • The heart pumps from the left ventricle, causing a rise in pressure as the new wave of blood leaves the heart.
  • The peak pressure is called the systolic pressure.
  • The left heart then begins to fill with blood (returned from the lungs) and pressure drops just before the next pulse (diastole).
  • The dicrotic notch represents closure of the aortic valve.

Blood Pressure

  • Mean arterial pressure is the average blood pressure in the arterial circulation.
  • "Normal" blood pressure is dependent on activity and has a diurnal variation.
  • Normal systolic pressure varies depending on the individual.

Blood Vessels

  • Arteries receive blood from the heart and need to withstand high pressure, high flow, and high shear.
  • Arteries have three tunics: intima, media, and adventitia.
  • Intima consists of endothelium monolayer and internal elastic lamina, comprised of connective tissue (elastin).
  • Media consists of smooth muscle, elastin, collagen, and external elastic lamina.
  • Adventitia consists of connective tissue (collagen and elastin).

Artery Types

  • Arteries branch (bifurcate) as they reduce in size.
  • Elastic (conduit) arteries have large, very thick walls, elastin to buffer pulse, and collagen for strength (e.g., aorta, ~10mm diameter).
  • Distributing (muscular) arteries have reduced medial thickness, contain elastin and collagen, and are involved in blood pressure regulation (e.g., carotid artery, 1-5 mm diameter).
  • Arterioles (resistance arteries) have thin media and are involved in setting peripheral resistance (e.g., central retinal artery, ~200 µm).

Capillaries

  • Capillaries are the smallest vessels (5-10 µm) with a single endothelial layer surrounded by a basement membrane.
  • They are the site of gas and metabolite exchange.
  • They represent the anastamosis between arterial and venous circulation.
  • Capillaries can be continuous, fenestrated, or sinusoid (levels of leakiness).

Venules

  • Venules are the smallest veins (5-15 µm) immediately downstream from capillaries.
  • They have intima, very thin media, and adventitia.
  • Venules are porous and fragile.
  • They merge/coalesce to form veins (e.g., central retinal venule).

Veins

  • Veins contain most of the blood in the body.
  • They have lower blood pressure than arteries.
  • They contain intima, thin media, and adventitia.
  • Adventitia thickens with increase in size.
  • Valves assist unidirectional blood flow to the heart.

Blood Flow

  • In the aorta, blood travels at 30 cm/sec.
  • In capillaries, blood travels at 0.3 mm/sec.
  • Slowed flow due to overall diameter in all capillaries >> aorta.
  • Laminar (smooth) flow is required in the capillary bed.
  • Elastin in the arteries dampens pulse waves.

The Arterial Pulse Wave

  • The heart pumps from the left ventricle, causing a rise in pressure as the new wave of blood leaves the heart.
  • The peak pressure is called the systolic pressure.
  • The left heart then begins to fill with blood (returned from the lungs) and pressure drops just before the next pulse (diastole).
  • The dicrotic notch represents closure of the aortic valve.

Blood Pressure

  • Mean arterial pressure is the average blood pressure in the arterial circulation.
  • "Normal" blood pressure is dependent on activity and has a diurnal variation.
  • Normal systolic pressure varies depending on the individual.

Lymphatic System Functions

  • Fluid homeostasis: lymphatic system returns interstitial fluids back to circulation after fluid flows out of arterioles
  • Two types of lymphatic vessels: initial lymphatics and collecting lymphatics
  • Initial lymphatics have:
    • Monolayer endothelial cells
    • No continuous basement membrane
    • Discontinuous junctions
    • Endothelial cells considered as primary valve
    • Anchored to extracellular tissue matrix by protein fibrillin
  • Collecting lymphatics have:
    • Monolayer endothelial cells
    • Surrounding basement membrane
    • Endothelial cells form continuous, zipper-like tight junctions
    • Contains 1-way valves

Immune System

  • Bone marrow:
    • Two components: haematopoietic and vascular
    • Haematopoietic component: haematopoietic stem cells, haematopoietic progenitor cells
    • Vascular component: located in bone marrow stroma, non-haematopoietic progenitor cells differentiating into mesenchymal tissue
    • Provides microenvironment for T cell maturation in absence of thymus
  • Immune cells in bone marrow:
    • CD4+ T cells: ~1.5%
    • CD8+ T cells: 2-2.5%
    • Regulatory T cells: ~0.5%
    • CD11c+ dendritic cells: 1-2%
    • B cells: ~1%
    • Plasma cells: ~0.5%
    • Natural killer T cells: 0.4-4%
    • Mesenchymal stem cells: 0.01-0.1%
    • Myeloid-derived suppressor cells: 20-30%
  • Thymus: maturation of T cells from bone marrow
  • Spleen:
    • Consists of red (~75%) and white (~25%) pulp
    • Red pulp filters old red blood cells, antigens, microorganisms
    • White pulp provides appropriate immune response to blood-borne pathogens
  • Tonsils and adenoid: trap pathogens in the nasal and oral passage
  • Lymph nodes: ~600 nodes along lymphatic vessels, filter lymph, store and transport B and T cells

Lymphatics in the Eye

  • Lymphatic vessels in the eye:
    • Conjunctiva: previously thought to be the only ocular structure with lymphatic vessels
    • Eyelids: classic drainage pathways, but lymphoscintigraphy has cast question on the classical lymphatics system
    • Cornea: Cor LYVE-1 staining
    • Limbus: mice eye, CD31-strong Prox-1- (blood vessels, red); Prox-1+CD31-weak (lymphatics, green)
    • Schlemm's canal: limbal BV, collector channel, Schlemm's canal
    • Ciliary body: red-smooth muscle, blue-blood vessels, green-lymphatic vessels
    • Meninges: flat endothelial cells that lack basal lamina, directly contacting lymph vessel lumen
    • Choroid: general consensus is net-like structures with a "pseudo-vessel" appearance, but evidence for functional lymphatic vessels disputed

Ocular Complications

  • Dry eyes: inflammatory disorder, chronic dry eyes can induce lymphangiogenesis in the cornea
  • Ocular tumour: lymphoma can be localized or systemic, be aware of new 'bump on the eyelid'

Lymphatic System Functions

  • Fluid homeostasis: lymphatic system returns interstitial fluids back to circulation after fluid flows out of arterioles
  • Two types of lymphatic vessels: initial lymphatics and collecting lymphatics
  • Initial lymphatics have:
    • Monolayer endothelial cells
    • No continuous basement membrane
    • Discontinuous junctions
    • Endothelial cells considered as primary valve
    • Anchored to extracellular tissue matrix by protein fibrillin
  • Collecting lymphatics have:
    • Monolayer endothelial cells
    • Surrounding basement membrane
    • Endothelial cells form continuous, zipper-like tight junctions
    • Contains 1-way valves

Immune System

  • Bone marrow:
    • Two components: haematopoietic and vascular
    • Haematopoietic component: haematopoietic stem cells, haematopoietic progenitor cells
    • Vascular component: located in bone marrow stroma, non-haematopoietic progenitor cells differentiating into mesenchymal tissue
    • Provides microenvironment for T cell maturation in absence of thymus
  • Immune cells in bone marrow:
    • CD4+ T cells: ~1.5%
    • CD8+ T cells: 2-2.5%
    • Regulatory T cells: ~0.5%
    • CD11c+ dendritic cells: 1-2%
    • B cells: ~1%
    • Plasma cells: ~0.5%
    • Natural killer T cells: 0.4-4%
    • Mesenchymal stem cells: 0.01-0.1%
    • Myeloid-derived suppressor cells: 20-30%
  • Thymus: maturation of T cells from bone marrow
  • Spleen:
    • Consists of red (~75%) and white (~25%) pulp
    • Red pulp filters old red blood cells, antigens, microorganisms
    • White pulp provides appropriate immune response to blood-borne pathogens
  • Tonsils and adenoid: trap pathogens in the nasal and oral passage
  • Lymph nodes: ~600 nodes along lymphatic vessels, filter lymph, store and transport B and T cells

Lymphatics in the Eye

  • Lymphatic vessels in the eye:
    • Conjunctiva: previously thought to be the only ocular structure with lymphatic vessels
    • Eyelids: classic drainage pathways, but lymphoscintigraphy has cast question on the classical lymphatics system
    • Cornea: Cor LYVE-1 staining
    • Limbus: mice eye, CD31-strong Prox-1- (blood vessels, red); Prox-1+CD31-weak (lymphatics, green)
    • Schlemm's canal: limbal BV, collector channel, Schlemm's canal
    • Ciliary body: red-smooth muscle, blue-blood vessels, green-lymphatic vessels
    • Meninges: flat endothelial cells that lack basal lamina, directly contacting lymph vessel lumen
    • Choroid: general consensus is net-like structures with a "pseudo-vessel" appearance, but evidence for functional lymphatic vessels disputed

Ocular Complications

  • Dry eyes: inflammatory disorder, chronic dry eyes can induce lymphangiogenesis in the cornea
  • Ocular tumour: lymphoma can be localized or systemic, be aware of new 'bump on the eyelid'

Lymphatic System Functions

  • Fluid homeostasis: lymphatic system returns interstitial fluids back to circulation after fluid flows out of arterioles
  • Two types of lymphatic vessels: initial lymphatics and collecting lymphatics
  • Initial lymphatics have:
    • Monolayer endothelial cells
    • No continuous basement membrane
    • Discontinuous junctions
    • Endothelial cells considered as primary valve
    • Anchored to extracellular tissue matrix by protein fibrillin
  • Collecting lymphatics have:
    • Monolayer endothelial cells
    • Surrounding basement membrane
    • Endothelial cells form continuous, zipper-like tight junctions
    • Contains 1-way valves

Immune System

  • Bone marrow:
    • Two components: haematopoietic and vascular
    • Haematopoietic component: haematopoietic stem cells, haematopoietic progenitor cells
    • Vascular component: located in bone marrow stroma, non-haematopoietic progenitor cells differentiating into mesenchymal tissue
    • Provides microenvironment for T cell maturation in absence of thymus
  • Immune cells in bone marrow:
    • CD4+ T cells: ~1.5%
    • CD8+ T cells: 2-2.5%
    • Regulatory T cells: ~0.5%
    • CD11c+ dendritic cells: 1-2%
    • B cells: ~1%
    • Plasma cells: ~0.5%
    • Natural killer T cells: 0.4-4%
    • Mesenchymal stem cells: 0.01-0.1%
    • Myeloid-derived suppressor cells: 20-30%
  • Thymus: maturation of T cells from bone marrow
  • Spleen:
    • Consists of red (~75%) and white (~25%) pulp
    • Red pulp filters old red blood cells, antigens, microorganisms
    • White pulp provides appropriate immune response to blood-borne pathogens
  • Tonsils and adenoid: trap pathogens in the nasal and oral passage
  • Lymph nodes: ~600 nodes along lymphatic vessels, filter lymph, store and transport B and T cells

Lymphatics in the Eye

  • Lymphatic vessels in the eye:
    • Conjunctiva: previously thought to be the only ocular structure with lymphatic vessels
    • Eyelids: classic drainage pathways, but lymphoscintigraphy has cast question on the classical lymphatics system
    • Cornea: Cor LYVE-1 staining
    • Limbus: mice eye, CD31-strong Prox-1- (blood vessels, red); Prox-1+CD31-weak (lymphatics, green)
    • Schlemm's canal: limbal BV, collector channel, Schlemm's canal
    • Ciliary body: red-smooth muscle, blue-blood vessels, green-lymphatic vessels
    • Meninges: flat endothelial cells that lack basal lamina, directly contacting lymph vessel lumen
    • Choroid: general consensus is net-like structures with a "pseudo-vessel" appearance, but evidence for functional lymphatic vessels disputed

Ocular Complications

  • Dry eyes: inflammatory disorder, chronic dry eyes can induce lymphangiogenesis in the cornea
  • Ocular tumour: lymphoma can be localized or systemic, be aware of new 'bump on the eyelid'

Kidney Structure

  • Kidney is bean-shaped and has three main regions: cortex, medulla, and papilla.
  • The nephron is the functional unit of the kidney, consisting of a glomerulus and a renal tubule.

Glomerular Filtration Barrier

  • The glomerular filtration barrier has three layers: endothelium, basement membrane, and epithelium.
  • Endothelium has pores 70-100 nm in diameter, allowing fluid and dissolved solutes to pass through.
  • Basement membrane is formed by the membranes of the endothelium and epithelium.
  • Epithelium has podocytes with foot processes, forming filtration slits 25-60 nm in diameter.

Glomerular Filtration Barrier Function

  • The glomerular filtration barrier prevents large molecules (e.g. proteins and cells) from passing through due to physical and electrostatic barriers.
  • Negatively charged glycoproteins in the barrier repel negatively charged proteins.

Kidney Function

  • The kidney's most important function is the reabsorption of sodium, which determines extracellular fluid volume.
  • The kidney also regulates electrolyte and water homeostasis, blood pH, and waste clearance.
  • It produces hormones including renin, erythropoietin, and vitamin D.

Diabetes

  • Diabetes is a condition where insulin production or sensitivity is affected, leading to increased blood sugar levels.
  • There are three types of diabetes: Type I, Type II, and Gestational.

Diabetic Retinopathy

  • Diabetic retinopathy is a condition where high blood sugar levels damage blood vessels in the eyes.

Liver Structure

  • The liver is the largest solid organ, weighing 1.5 kg in adults.
  • It receives 75% of its blood flow from the portal vein and 25% from the hepatic artery.
  • The functional unit of the liver is the liver lobule, which is cylindrical in shape and 0.8-2 mm in diameter.

Liver Cell Types

  • Hepatocytes make up 80% of liver cells and perform basic liver functions, such as storing glycogen and vitamins, and metabolizing lipids and drugs.
  • Hepatic stellate cells make up 5% of liver cells and store vitamin A and lipids.
  • Kupffer cells are immune sentinels, and liver sinusoidal endothelial cells form a permeable barrier between blood cells and hepatocytes.

Liver Function

  • The liver performs various functions, including glucose metabolism, lipid and cholesterol metabolism, protein synthesis, and haeme synthesis.
  • It also produces bile, which aids lipid absorption and bilirubin excretion.
  • The liver is responsible for red blood cell turnover and bilirubin storage.

Liver Function (continued)

  • The liver metabolizes drugs in two phases: Phase 1 involves oxidation or hydroxylation, and Phase 2 involves conjugation.

Jaundice

  • Jaundice is a condition where bilirubin builds up, causing yellow skin and conjunctiva.
  • It is common in newborns and can be caused by liver damage, bile flow interference, or excess bilirubin production in adults.
  • Treatment depends on the underlying cause.

Kidney Structure

  • Kidney is bean-shaped and has three main regions: cortex, medulla, and papilla.
  • The nephron is the functional unit of the kidney, consisting of a glomerulus and a renal tubule.

Glomerular Filtration Barrier

  • The glomerular filtration barrier has three layers: endothelium, basement membrane, and epithelium.
  • Endothelium has pores 70-100 nm in diameter, allowing fluid and dissolved solutes to pass through.
  • Basement membrane is formed by the membranes of the endothelium and epithelium.
  • Epithelium has podocytes with foot processes, forming filtration slits 25-60 nm in diameter.

Glomerular Filtration Barrier Function

  • The glomerular filtration barrier prevents large molecules (e.g. proteins and cells) from passing through due to physical and electrostatic barriers.
  • Negatively charged glycoproteins in the barrier repel negatively charged proteins.

Kidney Function

  • The kidney's most important function is the reabsorption of sodium, which determines extracellular fluid volume.
  • The kidney also regulates electrolyte and water homeostasis, blood pH, and waste clearance.
  • It produces hormones including renin, erythropoietin, and vitamin D.

Diabetes

  • Diabetes is a condition where insulin production or sensitivity is affected, leading to increased blood sugar levels.
  • There are three types of diabetes: Type I, Type II, and Gestational.

Diabetic Retinopathy

  • Diabetic retinopathy is a condition where high blood sugar levels damage blood vessels in the eyes.

Liver Structure

  • The liver is the largest solid organ, weighing 1.5 kg in adults.
  • It receives 75% of its blood flow from the portal vein and 25% from the hepatic artery.
  • The functional unit of the liver is the liver lobule, which is cylindrical in shape and 0.8-2 mm in diameter.

Liver Cell Types

  • Hepatocytes make up 80% of liver cells and perform basic liver functions, such as storing glycogen and vitamins, and metabolizing lipids and drugs.
  • Hepatic stellate cells make up 5% of liver cells and store vitamin A and lipids.
  • Kupffer cells are immune sentinels, and liver sinusoidal endothelial cells form a permeable barrier between blood cells and hepatocytes.

Liver Function

  • The liver performs various functions, including glucose metabolism, lipid and cholesterol metabolism, protein synthesis, and haeme synthesis.
  • It also produces bile, which aids lipid absorption and bilirubin excretion.
  • The liver is responsible for red blood cell turnover and bilirubin storage.

Liver Function (continued)

  • The liver metabolizes drugs in two phases: Phase 1 involves oxidation or hydroxylation, and Phase 2 involves conjugation.

Jaundice

  • Jaundice is a condition where bilirubin builds up, causing yellow skin and conjunctiva.
  • It is common in newborns and can be caused by liver damage, bile flow interference, or excess bilirubin production in adults.
  • Treatment depends on the underlying cause.

ATP and Energy Production

  • ATP (Adenosine Triphosphate) is the main energy unit in the body, with the human body using its body weight of ATP daily.
  • The average lifespan of an ATP molecule is 1-5 minutes, and it can be recycled around 300 times a day.
  • ATP is generated from the breakdown of glucose, proteins, and lipids.
  • The citric acid (Krebs) cycle is involved in ATP production.

Glucose Homeostasis

  • Glucose levels are regulated by hormones, including insulin (decreases blood glucose levels) and glucagon (increases blood glucose levels).
  • Organs involved in glucose homeostasis include the pancreas, liver, and muscles.

Pancreas Functions

  • The pancreas has exocrine (acinar) tissue, which produces enzymes for food digestion, and endocrine (islets) tissue, which produces hormones like insulin and glucagon.
  • Islets in the pancreas produce hormones, including insulin and glucagon.

Insulin and Glucagon Secretion

  • Insulin secretion is stimulated by high glucose levels, which increases intracellular ATP, closing β-cell KATP channels, and leading to insulin exocytosis.
  • Glucagon secretion is stimulated by low glucose levels, which decreases intracellular ATP, opening KATP channels, and leading to glucagon exocytosis.

Diabetes Mellitus

  • Diabetes mellitus is characterized by hyperglycaemia (high blood glucose levels).
  • There are three types of diabetes mellitus: Type 1 (juvenile/insulin-dependent), Type 2 (mature/non-insulin-dependent), and Gestational diabetes.

Type 1 Diabetes Mellitus

  • Type 1 DM is caused by the destruction of β-cells, resulting in no insulin production.
  • It is an autoimmune disease with a low incidence (~1/400).
  • Treatment options include insulin injection, pancreas transplant, and islet transplant.

Type 2 Diabetes Mellitus

  • Type 2 DM is associated with obesity, which increases insulin resistance.
  • It has a high incidence and is characterized by two main pathophysiological mechanisms: insulin resistance and reduced insulin secretion.
  • Complications of Type 2 DM include acute and chronic complications, such as nonketotic hyperosmolar coma.

ATP and Energy Production

  • ATP (Adenosine Triphosphate) is the main energy unit in the body, with the human body using its body weight of ATP daily.
  • The average lifespan of an ATP molecule is 1-5 minutes, and it can be recycled around 300 times a day.
  • ATP is generated from the breakdown of glucose, proteins, and lipids.
  • The citric acid (Krebs) cycle is involved in ATP production.

Glucose Homeostasis

  • Glucose levels are regulated by hormones, including insulin (decreases blood glucose levels) and glucagon (increases blood glucose levels).
  • Organs involved in glucose homeostasis include the pancreas, liver, and muscles.

Pancreas Functions

  • The pancreas has exocrine (acinar) tissue, which produces enzymes for food digestion, and endocrine (islets) tissue, which produces hormones like insulin and glucagon.
  • Islets in the pancreas produce hormones, including insulin and glucagon.

Insulin and Glucagon Secretion

  • Insulin secretion is stimulated by high glucose levels, which increases intracellular ATP, closing β-cell KATP channels, and leading to insulin exocytosis.
  • Glucagon secretion is stimulated by low glucose levels, which decreases intracellular ATP, opening KATP channels, and leading to glucagon exocytosis.

Diabetes Mellitus

  • Diabetes mellitus is characterized by hyperglycaemia (high blood glucose levels).
  • There are three types of diabetes mellitus: Type 1 (juvenile/insulin-dependent), Type 2 (mature/non-insulin-dependent), and Gestational diabetes.

Type 1 Diabetes Mellitus

  • Type 1 DM is caused by the destruction of β-cells, resulting in no insulin production.
  • It is an autoimmune disease with a low incidence (~1/400).
  • Treatment options include insulin injection, pancreas transplant, and islet transplant.

Type 2 Diabetes Mellitus

  • Type 2 DM is associated with obesity, which increases insulin resistance.
  • It has a high incidence and is characterized by two main pathophysiological mechanisms: insulin resistance and reduced insulin secretion.
  • Complications of Type 2 DM include acute and chronic complications, such as nonketotic hyperosmolar coma.

Muscle Cells

  • Specialized cells that contract, responsible for body movement and controlling shape/size of internal organs
  • Elongated shape, arranged in parallel array

Muscle Types

  • 2 classes: striated and smooth
  • Striated muscles:
    • Exhibit cross striation, arranged in bundles
    • 2 subtypes: skeletal (attached to bone) and cardiac (heart muscle)
  • Smooth muscles:
    • No cross striation, arranged in sheets
    • Found in internal organs (except heart)

Skeletal Muscle

  • Elongated muscle cells embedded in connective tissue framework
  • Comprises collagen fibers, fibroblasts, neurovascular bundles
  • 40% of body weight, responsible for movement of limbs and digits, maintenance of body posture

Skeletal Muscle Fibers

  • Categorized by diameter and natural color:
    • Red fibers: small, with large amounts of myoglobin, cytochromes, and mitochondria (slow twitch)
    • White fibers: large, with less myoglobin, fewer cytochromes and mitochondria (fast twitch)
    • Intermediate fibers: intermediate in size, with myoglobin, cytochromes, and mitochondrial numbers between red and white fibers

Cardiac Muscle

  • Heart muscle, striated
  • Differ from other muscle types:
    • Inherent rhythmicity, spontaneous contraction via sinus node in right atrium
    • Cellular membrane of myocytes intertwined, form intercalated discs – synchronized contraction

Smooth Muscle

  • No striation
  • Not under voluntary control, regulated by autonomic nervous system
  • Organized as single unit (visceral) or multiunit
    • Visceral: muscle fibers joined by gap junction, contracts as single unit
    • Multiunit (e.g. iris): no gap junction, independent contraction

Neurons

  • Classified morphologically
  • Information passes from dendrite to axonal terminal
  • Myelin sheath allows faster electrical impulse transmission

Neuron Functional Types

  • Sensory neurons (afferent): receive sensory input at dendritic terminals, information moves towards CNS
  • Motor neurons (efferent): send impulses to muscles, glands, other neurons, information moves away from CNS
  • Interneurons: located within CNS, establish networks between sensory and motor neurons

Synapse

  • Neurotransmitters have specific receptors, excitatory or inhibitory, promote or prevent action potential
  • Common neurotransmitters: biogenic amines, amino acids, nucleotides, gases, neuropeptides

Glial Cells

  • Non-neuronal, support cells in CNS and PNS
  • CNS: astrocytes, oligodendrocytes, ependymal cells, microglia
  • PNS: Schwann cells, satellite cells
  • Functions:
    • Astrocytes: maintain blood-brain barrier (BBB) and extracellular homeostasis
    • Oligodendrocytes: myelinate axons
    • Ependymal cells: produce cerebrospinal fluid
    • Microglia: macrophage, clear cell debris and dead neurons
    • Schwann cells: myelinate PNS axons
    • Satellite cells: maintain extracellular homeostasis

Epithelial Tissue

  • Avascular, composed of specialized junctions, apical surface, and basement membrane
  • Two types: surface epithelium and glandular epithelium
  • Origins: surface epithelium from ectoderm, mesoderm, and endoderm; glandular epithelium from ectoderm, mesoderm, and endoderm
  • Functions: protection, secretion, transcellular transport, and absorption
  • Polarity: most epithelial cells have a top (apical) and bottom (basal) surface

Classification of Epithelia

  • Classified by number of cell layers and shape of cells in the surface layer
  • Simple epithelia: one cell layer thick, squamous, cuboidal, or columnar
  • Stratified epithelia: two or more cell layers, classified by the shape of cells in the surface layer

Simple Epithelia

  • Found in interfaces for selective diffusion, absorption, and/or secretion
  • Squamous: found in endothelial lining of blood vessels and mesothelial lining of body cavities
  • Cuboidal: function in secretion/absorption, found in collecting tubules of the kidney, ducts draining exocrine glands, and under the anterior lens capsule
  • Columnar: function in secretion/absorption/protection, found in the internal surface of the GI tract
  • Pseudostratified: appears as if cells are not in contact with the basal lamina, found in the upper respiratory tract and vas deferens

Stratified Epithelia

  • Mostly involved in providing protection
  • Classified based on the most superficial cells
  • Squamous: outer layer squamous cell, function in protection to mechanical stress and desiccation, keratinized or non-keratinized
  • Columnar: inner layers can be other epithelial cell types, cells in apical layer connected by gap junctions and desmosomes, functions in protection/secretion
  • Cuboidal: inner layers can be other epithelial cell types, cells in apical layer connected by gap junctions and desmosomes, main function: secretion
  • Transitional/Transitional epithelium: cells can change shape depending on tissue distention, found in the epithelial lining of the lower urinary tract (urothelium)

Glandular Epithelium

  • Simplest form: invagination of the surface epithelium
  • Two groups: exocrine and endocrine
  • Exocrine glands: release content onto an epithelial surface directly or via a duct, classified according to the nature of their secretion, mode of secretion, and number of cells
  • Endocrine glands: release into the bloodstream, do not have ducts, major endocrine glands of the body include pituitary, adrenal, thyroid, parathyroid, pineal, and pancreas

Connective Tissue (CT)

  • Provides support: general scaffolding, tensile strength, elasticity, and space filling
  • Consists of cells surrounded by extracellular matrix (ECM)
  • 3 classes: loose, dense, and specialized
  • Loose CT: most common type, loosely packed fibers separated by large amount of ground substance, provides mechanical strength with physical and metabolic support
  • Dense CT: high proportion of fibers, little ground substance, 2 subtypes: regular and irregular
  • Regular dense CT: collagen bundles arranged in one general direction, maximal tensile strength, found in tendons and corneal stroma
  • Irregular dense CT: collagen bundles oriented in various 3D arrays, enables tissue to withstand tension from different directions, found in dermis and sclera

Basement Membrane (BM)

  • Specialized collection of connective tissue fibers and matrix located subjacent to the basal portion of epithelial cells
  • Found between cell and underlying CT, also around endothelium, muscle cells, fat, and peripheral nerve cells
  • 3 layers: lamina lucida, lamina densa, and lamina fibroreticularis/reticular lamina
  • Functions: physically binds the epithelium to the underlying tissue, controls epithelial growth and differentiation, regulates permeability
  • Components: type IV collagen, laminin, nidogen/entactin, fibronectin, glycoproteins, and proteoglycans

Epithelial Tissue

  • Avascular, composed of specialized junctions, apical surface, and basement membrane
  • Two types: surface epithelium and glandular epithelium
  • Origins: surface epithelium from ectoderm, mesoderm, and endoderm; glandular epithelium from ectoderm, mesoderm, and endoderm
  • Functions: protection, secretion, transcellular transport, and absorption
  • Polarity: most epithelial cells have a top (apical) and bottom (basal) surface

Classification of Epithelia

  • Classified by number of cell layers and shape of cells in the surface layer
  • Simple epithelia: one cell layer thick, squamous, cuboidal, or columnar
  • Stratified epithelia: two or more cell layers, classified by the shape of cells in the surface layer

Simple Epithelia

  • Found in interfaces for selective diffusion, absorption, and/or secretion
  • Squamous: found in endothelial lining of blood vessels and mesothelial lining of body cavities
  • Cuboidal: function in secretion/absorption, found in collecting tubules of the kidney, ducts draining exocrine glands, and under the anterior lens capsule
  • Columnar: function in secretion/absorption/protection, found in the internal surface of the GI tract
  • Pseudostratified: appears as if cells are not in contact with the basal lamina, found in the upper respiratory tract and vas deferens

Stratified Epithelia

  • Mostly involved in providing protection
  • Classified based on the most superficial cells
  • Squamous: outer layer squamous cell, function in protection to mechanical stress and desiccation, keratinized or non-keratinized
  • Columnar: inner layers can be other epithelial cell types, cells in apical layer connected by gap junctions and desmosomes, functions in protection/secretion
  • Cuboidal: inner layers can be other epithelial cell types, cells in apical layer connected by gap junctions and desmosomes, main function: secretion
  • Transitional/Transitional epithelium: cells can change shape depending on tissue distention, found in the epithelial lining of the lower urinary tract (urothelium)

Glandular Epithelium

  • Simplest form: invagination of the surface epithelium
  • Two groups: exocrine and endocrine
  • Exocrine glands: release content onto an epithelial surface directly or via a duct, classified according to the nature of their secretion, mode of secretion, and number of cells
  • Endocrine glands: release into the bloodstream, do not have ducts, major endocrine glands of the body include pituitary, adrenal, thyroid, parathyroid, pineal, and pancreas

Connective Tissue (CT)

  • Provides support: general scaffolding, tensile strength, elasticity, and space filling
  • Consists of cells surrounded by extracellular matrix (ECM)
  • 3 classes: loose, dense, and specialized
  • Loose CT: most common type, loosely packed fibers separated by large amount of ground substance, provides mechanical strength with physical and metabolic support
  • Dense CT: high proportion of fibers, little ground substance, 2 subtypes: regular and irregular
  • Regular dense CT: collagen bundles arranged in one general direction, maximal tensile strength, found in tendons and corneal stroma
  • Irregular dense CT: collagen bundles oriented in various 3D arrays, enables tissue to withstand tension from different directions, found in dermis and sclera

Basement Membrane (BM)

  • Specialized collection of connective tissue fibers and matrix located subjacent to the basal portion of epithelial cells
  • Found between cell and underlying CT, also around endothelium, muscle cells, fat, and peripheral nerve cells
  • 3 layers: lamina lucida, lamina densa, and lamina fibroreticularis/reticular lamina
  • Functions: physically binds the epithelium to the underlying tissue, controls epithelial growth and differentiation, regulates permeability
  • Components: type IV collagen, laminin, nidogen/entactin, fibronectin, glycoproteins, and proteoglycans

Embryonic Development

  • 4 stages of embryonic development:
  • Fertilisation: sperm + egg forms a zygote
  • Cleavage: multiple rounds of mitotic cell division, resulting in a blastula
  • Gastrulation: rearrangement of cells to form embryonic tissue layers
  • Organogenesis: organ and tissue formation
  • At 5 days post-fertilisation, the embryo consists of an internal cell mass (forms the embryo) and trophoblasts/outer layer cells (forms the placenta)

Embryogenesis

  • Occurs between 2-8 weeks post-fertilisation
  • Inner cell mass differentiates into the embryo
  • Bilaminar disc forms within the amniotic cavity, giving the embryo its first orientation (dorsal/epiblast and ventral/hypoblast axis)
  • Gastrulation: proliferation and migration of epiblast into 3 germ layers, resulting in a trilaminar mass of cells (gastrula)

Germ Layers

  • Ectoderm:
  • Differentiates into 2 parts: surface ectoderm and neural tube
  • Formations: retina, epithelial linings of iris and ciliary body, optic nerve, lens, corneal and conjunctival epithelium, eyelids
  • Mesoderm:
  • Formations: sclera, choroid, corneal stroma, vitreous, extraocular muscles
  • Endoderm:
  • Folds to form the subdivisions of the primitive gut (foregut, midgut, hindgut)
  • Formations: pharynx, lower respiratory tract, esophagus, stomach, duodenum, liver, pancreas, small intestine, large intestine

Eye Development

  • Week 4:
  • Bilateral indentations form (optical grooves/sulci) on each side of the forebrain
  • Optic vesicles develop and interact with surface ectoderm
  • Lens placode forms, inducing the optic vesicle to thicken and form the retinal disc
  • Week 5:
  • Invagination of the optic vesicle forms the optic cup
  • Development of the lens placode triggers invagination of the optic vesicle
  • Optic fissure begins to close
  • Week 6:
  • Invaginating lens placode forms the lens vesicle
  • The hyaloid artery wraps around the posterior lens
  • Optic fissure closure continues
  • Week 7:
  • Retina develops from the dorsal neuroectoderm of the optic vesicle
  • RPE (retinal pigment epithelium) forms a single layer of cuboidal cells
  • Bruch's membrane (primitive) arises
  • Sensory retina thickens
  • Week 8:
  • RPE matures
  • Sensory retina: outer and inner neuroblastic layers develop
  • Primary lens fibers form, obliterating the cavity within the lens vesicle
  • Periocular mesenchyme: formation of choroidal vasculature, corneal stroma, endothelium, trabecular meshwork, and Schlemm's canal

Critical Period of Eye Development

  • Week 4 to 8: critical period of eye development
  • Vision is fine-tuned via visual input after birth

Embryonic Development

  • 4 stages of embryonic development:
  • Fertilisation: sperm + egg forms a zygote
  • Cleavage: multiple rounds of mitotic cell division, resulting in a blastula
  • Gastrulation: rearrangement of cells to form embryonic tissue layers
  • Organogenesis: organ and tissue formation
  • At 5 days post-fertilisation, the embryo consists of an internal cell mass (forms the embryo) and trophoblasts/outer layer cells (forms the placenta)

Embryogenesis

  • Occurs between 2-8 weeks post-fertilisation
  • Inner cell mass differentiates into the embryo
  • Bilaminar disc forms within the amniotic cavity, giving the embryo its first orientation (dorsal/epiblast and ventral/hypoblast axis)
  • Gastrulation: proliferation and migration of epiblast into 3 germ layers, resulting in a trilaminar mass of cells (gastrula)

Germ Layers

  • Ectoderm:
  • Differentiates into 2 parts: surface ectoderm and neural tube
  • Formations: retina, epithelial linings of iris and ciliary body, optic nerve, lens, corneal and conjunctival epithelium, eyelids
  • Mesoderm:
  • Formations: sclera, choroid, corneal stroma, vitreous, extraocular muscles
  • Endoderm:
  • Folds to form the subdivisions of the primitive gut (foregut, midgut, hindgut)
  • Formations: pharynx, lower respiratory tract, esophagus, stomach, duodenum, liver, pancreas, small intestine, large intestine

Eye Development

  • Week 4:
  • Bilateral indentations form (optical grooves/sulci) on each side of the forebrain
  • Optic vesicles develop and interact with surface ectoderm
  • Lens placode forms, inducing the optic vesicle to thicken and form the retinal disc
  • Week 5:
  • Invagination of the optic vesicle forms the optic cup
  • Development of the lens placode triggers invagination of the optic vesicle
  • Optic fissure begins to close
  • Week 6:
  • Invaginating lens placode forms the lens vesicle
  • The hyaloid artery wraps around the posterior lens
  • Optic fissure closure continues
  • Week 7:
  • Retina develops from the dorsal neuroectoderm of the optic vesicle
  • RPE (retinal pigment epithelium) forms a single layer of cuboidal cells
  • Bruch's membrane (primitive) arises
  • Sensory retina thickens
  • Week 8:
  • RPE matures
  • Sensory retina: outer and inner neuroblastic layers develop
  • Primary lens fibers form, obliterating the cavity within the lens vesicle
  • Periocular mesenchyme: formation of choroidal vasculature, corneal stroma, endothelium, trabecular meshwork, and Schlemm's canal

Critical Period of Eye Development

  • Week 4 to 8: critical period of eye development
  • Vision is fine-tuned via visual input after birth

Anatomy of the Skull and Orbit

  • The skull consists of 22 bones united at immobile joints called sutures.
  • The 22 bones are divided into:
    • Cranium (8 bones): protects the brain
    • Facial bones (14 bones): "hang" off the cranium
  • Cranial bones:
    • Frontal bone x 1
    • Parietal bones x 2
    • Occipital bone x 1
    • Temporal bones x 2
    • Sphenoid bone x 1
    • Ethmoid bone x 1
  • Facial bones:
    • Zygomatic bones x 2
    • Maxillary bones x 2
    • Nasal bones x 2
    • Lacrimal bones x 2
    • Vomer x 1
    • Palatine bones x 2
    • Inferior conchae x 2
    • Mandible x 1

The Orbit

  • The orbit is a pyramidal/conical shaped cavity with dimensions of approximately 40mm x 40mm x 40mm.
  • The eye occupies about 1/5 of the orbit, while the remaining 4/5 is occupied by:
    • Optic nerve
    • Extraocular muscles
    • Lacrimal gland
    • Nerves
    • Connective tissue (orbital fat)

Orbital Bones

  • The 7 bones that make up the orbit are:
    • Maxillary bone
    • Zygomatic bone
    • Lacrimal bone
    • Ethmoid bone
    • Palatine bone
    • Sphenoid bone
    • Frontal bone
  • These bones are designed to protect the globe.

Orbital Margin

  • Supraorbital margin:
    • Formed by the frontal bone
    • Note supraorbital notch (open) or foramen (closed)
    • Allows passage of the supraorbital neurovascular bundle
  • Infraorbital margin:
    • Formed by the zygomatic bone (laterally) and maxillary bone (medially)
  • Lateral margin:
    • Formed by the zygomatic process of the frontal bone and frontal process of the zygomatic bone
  • Medial margin:
    • Formed by the maxillary process of the frontal bone and frontal process of the maxillary bone

Walls of the Orbit

  • Roof:
    • Composed of 2 bones: frontal bone and lesser wing of sphenoid
    • Contains optic canal
  • Floor:
    • Composed of 3 bones: maxillary bone, zygomatic bone, and palatine bone
    • Very thin, most susceptible to fracture
  • Medial wall:
    • Composed of 5 bones: ethmoid bone, lacrimal bone, body of sphenoid bone, frontal bone, and maxillary bone
    • Thin wall
  • Lateral wall:
    • Composed of 2 bones: greater wing of sphenoid and zygomatic bone
    • Thickest wall for protection

Orbital Fracture

  • Two theories: hydraulic and buckling
  • History of blunt trauma
  • Floor most susceptible to fracture, followed by medial wall
  • Symptoms: bruising, tenderness, redness, double vision
  • CT scans needed for diagnosis

Openings into the Orbital Cavity

  • Optic canal:
    • Within the lesser wing of the sphenoid
    • Transmits the optic nerve and ophthalmic artery
  • Superior orbital fissure:
    • Between the lesser and greater wings of the sphenoid
    • Transmits most of the other vascular and neural structures into the orbit
  • Inferior orbital fissure:
    • Between the greater wing of sphenoid and maxillary bone
    • Mainly transmits inferior ophthalmic vein and maxillary division of the trigeminal nerve
  • Foramina:
    • Anterior and posterior ethmoid
    • Transmit ethmoidal nerves and arteries

Nasal Cavity and Tear Drainage

  • Nasal cavity:
    • Internal component of the nose
    • Contains 4 sinuses
    • Sinus functions:
      • Support immune defense
      • Humidify inspired air
      • Voice resonance
      • Lighten skull
  • Tear drainage:
    • Punctum → lacrimal canaliculi → lacrimal sac → nasolacrimal duct → nasal cavity
    • Ducts may be blocked, lacrimal lavage to clear the blockage

Anatomy of the Skull and Orbit

  • The skull consists of 22 bones united at immobile joints called sutures.
  • The 22 bones are divided into:
    • Cranium (8 bones): protects the brain
    • Facial bones (14 bones): "hang" off the cranium
  • Cranial bones:
    • Frontal bone x 1
    • Parietal bones x 2
    • Occipital bone x 1
    • Temporal bones x 2
    • Sphenoid bone x 1
    • Ethmoid bone x 1
  • Facial bones:
    • Zygomatic bones x 2
    • Maxillary bones x 2
    • Nasal bones x 2
    • Lacrimal bones x 2
    • Vomer x 1
    • Palatine bones x 2
    • Inferior conchae x 2
    • Mandible x 1

The Orbit

  • The orbit is a pyramidal/conical shaped cavity with dimensions of approximately 40mm x 40mm x 40mm.
  • The eye occupies about 1/5 of the orbit, while the remaining 4/5 is occupied by:
    • Optic nerve
    • Extraocular muscles
    • Lacrimal gland
    • Nerves
    • Connective tissue (orbital fat)

Orbital Bones

  • The 7 bones that make up the orbit are:
    • Maxillary bone
    • Zygomatic bone
    • Lacrimal bone
    • Ethmoid bone
    • Palatine bone
    • Sphenoid bone
    • Frontal bone
  • These bones are designed to protect the globe.

Orbital Margin

  • Supraorbital margin:
    • Formed by the frontal bone
    • Note supraorbital notch (open) or foramen (closed)
    • Allows passage of the supraorbital neurovascular bundle
  • Infraorbital margin:
    • Formed by the zygomatic bone (laterally) and maxillary bone (medially)
  • Lateral margin:
    • Formed by the zygomatic process of the frontal bone and frontal process of the zygomatic bone
  • Medial margin:
    • Formed by the maxillary process of the frontal bone and frontal process of the maxillary bone

Walls of the Orbit

  • Roof:
    • Composed of 2 bones: frontal bone and lesser wing of sphenoid
    • Contains optic canal
  • Floor:
    • Composed of 3 bones: maxillary bone, zygomatic bone, and palatine bone
    • Very thin, most susceptible to fracture
  • Medial wall:
    • Composed of 5 bones: ethmoid bone, lacrimal bone, body of sphenoid bone, frontal bone, and maxillary bone
    • Thin wall
  • Lateral wall:
    • Composed of 2 bones: greater wing of sphenoid and zygomatic bone
    • Thickest wall for protection

Orbital Fracture

  • Two theories: hydraulic and buckling
  • History of blunt trauma
  • Floor most susceptible to fracture, followed by medial wall
  • Symptoms: bruising, tenderness, redness, double vision
  • CT scans needed for diagnosis

Openings into the Orbital Cavity

  • Optic canal:
    • Within the lesser wing of the sphenoid
    • Transmits the optic nerve and ophthalmic artery
  • Superior orbital fissure:
    • Between the lesser and greater wings of the sphenoid
    • Transmits most of the other vascular and neural structures into the orbit
  • Inferior orbital fissure:
    • Between the greater wing of sphenoid and maxillary bone
    • Mainly transmits inferior ophthalmic vein and maxillary division of the trigeminal nerve
  • Foramina:
    • Anterior and posterior ethmoid
    • Transmit ethmoidal nerves and arteries

Nasal Cavity and Tear Drainage

  • Nasal cavity:
    • Internal component of the nose
    • Contains 4 sinuses
    • Sinus functions:
      • Support immune defense
      • Humidify inspired air
      • Voice resonance
      • Lighten skull
  • Tear drainage:
    • Punctum → lacrimal canaliculi → lacrimal sac → nasolacrimal duct → nasal cavity
    • Ducts may be blocked, lacrimal lavage to clear the blockage

Sclera

  • Whish outer coat of the eye
  • Derived from Greek "skleros" meaning hard
  • Dense, irregular connective tissue (CT)

Functions of Sclera

  • Protection: tough barrier separating intraocular structures from orbital walls and the outside world
  • Refractive stability: keeps eye length stable during changes in intraocular pressure and blood pressure, and during eye movements and accommodation
  • Conduit for nerves and vessels: allows nerve and vessel access to underlying ocular structures
  • Anchor for extraocular muscles: provides stable anchorage for extraocular muscle tendons, contributing to stability of torsional movements
  • Anchor for ciliary muscle: opposes contractile forces of ciliary muscle, allowing stable accommodation
  • Facilitates ocular drainage: majority of aqueous outflow through intrascleral venous plexus to the episcleral plexus

Openings in the Sclera

  • Minor foramina: allow blood vessels and nerves to pierce the eyeball
  • Two major foramina: anterior scleral foramen (cornea) and posterior scleral foramen (scleral canal)

Layers of the Sclera

  • Episclera: outermost layer, merges with the underlying scleral stroma
  • Scleral stroma: dense, irregular CT
  • Lamina fusca: innermost layer, regarded as part of choroid by some, but separated from choroid by perichoroidal space

Biochemical Composition of the Sclera

  • Collagen (around 90% of scleral dry weight, predominantly type I)
  • Proteoglycans and glycosaminoglycans (around 1% of dry weight)
  • Glycoproteins (e.g. fibronectin)
  • Fibroblasts, myofibroblasts, and some melanocytes
  • Non-collagenous proteins (e.g. elastin, proteases, etc.)
  • Water

Scleral Cells

  • Fibroblasts: synthesise collagen, elastic, and reticular fibres, reside close to collagen matrices
  • Myofibroblasts: modified fibroblasts, synthesise collagen, express contractile proteins (e.g. α-smooth muscle actin), present in mammals, including humans

Scleral Collagens

  • Structural unit: tropocollagen/collagen (~3 intertwined polypeptide chains, rich in amino acids proline and hydroxyproline)
  • Staggered collagen molecules assemble into a fibril

Scleral Proteoglycans

  • ~0.7-0.9% of the total scleral dry weight
  • Modulate collagen fibril assembly and arrangement
  • Aggrecan, biglycan, and decorin: sequester water within the scleral ECM, highest concentration in the posterior sclera, possibly maintaining posterior pole flexibility

Learn about the structure and function of photoreceptors in the outer retina, including cones and rods, and how they convert light energy into electrical energy. Explore the differences between the fovea and periphery, and the concept of dark current.

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