OV1015_OcularTissueTypes_pj_v0_1_c (4).pptx

OV1015: Ocular Tissue Types Pete Jones 〈[email protected]〉 Preamble 2 Aim(s): 1. To be able to understand and describe each of the four tissue types 2. To be able to identify their structure and primary functions;...

OV1015: Ocular Tissue Types Pete Jones 〈[email protected]〉 Preamble 2 Aim(s): 1. To be able to understand and describe each of the four tissue types 2. To be able to identify their structure and primary functions; to be able to give examples of each 3. To be familiar with the roles these four tissue types play in the human visual system 1. Light rays impinge on the surface of the eye and encounter the ‘tear film’. 2. The outer coat of the eye is mostly opaque sclera At the front of the eye this is modified into the transparent cornea The corneoscleral junction is known as the limbus 3. After traversing the anterior chamber, light reaches the lens 4. The cornea and the lens act together to focus light on the retina which lines the posterior 2/3rds of the globe 5. Between the retina and the sclera is the choroid, which contains the vascular (blood) supply to the outer retina. 6. In order to be transparent the cornea and lens are avascular. They receive their nutrients from the clear aqueous humour, which fills the anterior chamber. 7. The bulk of the eye, posterior to the aqueous, is filled with the jelly like vitreous humour. 8. There are also 2 groups of muscle within the eye. Muscles of the iris can alter the size of the pupil 9. While muscles in the ciliary body can change the shape of the lens during the process of accommodation. The Ocular Adnexa: The parts of the orbital region that are outside the eyeball, including: Extraocular muscles (eye movement) Lacrimal gland (tear film production) Eyelids (spreading of tear film) Conjunctiva (additional tear film production + immune response) Eyebrows & eyelashes (barriers to contaminants + facial expression) OV1113: Tissue Types ▪ Overview: The 4 types of tissue and their roles ▪ Nervous tissue ▪ Muscle tissue ▪ Connective tissue Proper connective tissue ▪ Epithelial tissue Covering epithelia Glandular epithelia 12 Definition 13 Tissue [ tish-yoo ]  A group of similar cells with a common purpose  Four main types: nervous tissue controls muscle tissue moves connective tissue supports epithelial tissue covers gross simplification OV1113: Tissue Types ▪ Overview: The 4 types of tissue and their roles ▪ Nervous tissue ▪ Muscle tissue ▪ Connective tissue Proper connective tissue ▪ Epithelial tissue Covering epithelia Glandular epithelia 14 Nervous Tissue 15 Nervous tissue  The main component of the nervous system (brain, spinal cord, & nerves)  Made up of two main components: 1. Nerve cells, more commonly known as neurons 2. Support cells, more commonly known as glia Nervous Tissue 16 Nervous tissue  The main component of the nervous system (brain, spinal cord, & nerves)  Made up of two main components : 1. Nerve cells, more commonly known as neurons 2. Support cells, more commonly known as glia  Glia refers to a family of cells that support, protect, and insulate the delicate neurons Nervous Tissue 17 Nervous tissue  The main component of the nervous system (brain, spinal cord, & nerves)  Made up of two main components : 1. Nerve cells, more commonly known as neurons 2. Support cells, more commonly known as glia  Glia refers to a family of cells that support, protect, and insulate the delicate neurons  Neurons generate and transmit electrical impulses. Networks of neurons can perform complex computations  To be discussed more in future lectures! Nervous Tissue: Ocular examples 18 Nervous tissue in the eye  Nerve cells are associated with most ocular structures, both in terms of: Efferent (motor) pathways; e.g., ciliary body Afferent (sensory) pathways; e.g., cornea  The retina in particular is mostly composed of nervous tissue Nervous Tissue: Ocular examples 19 Nervous tissue in the eye  Nerve cells are associated with most ocular structures, both in terms of: Efferent (motor) pathways; e.g., ciliary body Afferent (sensory) pathways; e.g., cornea  The retina in particular is mostly composed of nervous tissue Made up of different types of neurons (ganglia, bipolar cells, photoreceptors, etc.) Arranged in layers with the photoreceptors at the back(!) OV1113: Tissue Types ▪ Overview: The 4 types of tissue and their roles ▪ Nervous tissue ▪ Muscle tissue ▪ Connective tissue Proper connective tissue ▪ Epithelial tissue Covering epithelia Glandular epithelia 20 Muscle Tissue 21 Muscle tissue  Tissue composed of myoctes (muscle cells) – cells that contract to produce force and motion.  Three types: 1. Skeletal muscle – attached to skeleton. Striated in appearance. Capable of generating a lot of force 2. Smooth – lines hollow organs. Non-striated in appearance. Capable of sustained activity (e.g., continuously pushing food through digestive system) 3. Cardiac – within heart. Striated branching fibres. Myogenic (activation arising locally from within the muscle tissue, rather than from external nerve impulses)  To be discussed more in dedicated lecture: “muscle” Muscle Tissue 22 Muscle tissue  Muscle is a good example of how a single tissue type can serve a wide variety of functions  Muscle “moves”, but in doing so is responsible for many tasks, including: Locomotion Posture (muscle tone) Generating heat (shivering) Retaining heat (hair follicles) Nutrition – propelling substances (peristalsis) Respiration (breathing) Circulation (pumping blood) Regulating sight and hearing Facial expression Muscle Tissue: Ocular examples 23 Skeletal muscle tissue in the eye  Skeletal (striated, strong force) muscles exist in the eye in the form of:  The 6 extraocular muscles that control eye movements Muscle Tissue: Ocular examples 24 Skeletal muscle tissue in the eye  Skeletal (striated, strong force) muscles exist in the eye in the form of:  The 6 extraocular muscles that control eye movements  Some of the eyelid muscles (e.g., orbicularis occuli, which closes the eyelids) Though some other eyelid muscles are smooth (e.g., the superior tarsal muscle that helps raise the upper eyelid) Muscle Tissue: Ocular examples 25 Smooth muscle tissue in the eye  Smooth (non-striated, sustained activity) muscles exist in the eye in the form of:  Iris – for controlling pupil size to regulate the amount of incoming light  Ciliary body – for changing the shape/focal power of the lens (accommodation) Ciliary body Iris OV1113: Tissue Types ▪ Overview: The 4 types of tissue and their roles ▪ Nervous tissue ▪ Muscle tissue ▪ Connective tissue Proper connective tissue ▪ Epithelial tissue Covering epithelia Glandular epithelia 26 Connective Tissue 27 Connective tissue overview  Connective tissue (1) binds and supports; (2) protects; (3) insulates; (4) stores reserves of essential elements (water, salt, fat); and (5) transports substances within the body.  Other tissue types are made up mainly of cells. Connective tissue is different as it is largely (but not completely!) acellular  It is made of 3 things: 1. Ground substance Extracellular matrix 2. Fibres 3. Cells The thing that makes connective tissue extremely tough and durable Connective Tissue 28 Ground substance  “stuff”  The unstructured material that fills the space between the cells and contains the fibres. Made up of: Interstitial fluid (containing dissolved nutrients etc.) Cell adhesion proteins (biological “glue” that binds connective tissue cells to the extracellular matrix) Proteoglycans & glycoproteins that trap water  Can vary in consistency from a watery fluid to viscous gel The vitreous humour is composed largely of a gel- like ground substance. Connective Tissue 29 Fibres Strands of proteins. Three types: 1. Collagen fibres: Thickest of the connective tissue fibres, and also the strongest and most abundant. Collagen accounts for over 30% of the body’s dry weight of protein. 2. Reticular fibres: Thicker than elastic but thinner than the collagen fibres. Often form fuzzy “nets” (reticul = “network”) that cradle other tissues. Once thought to be a distinct type of fibre but are now known to be very fine collagen fibres. 3. Elastic fibres: composed of elastin. The fibres, which are thinner than collagen, stretch readily and return to their original form after a force is removed. Ideal for supporting moving structures (e.g., skin, lungs, blood vessels, etc.) Connective Tissue 30 Cells  Fibroblasts: This is the fundamental cell type of connective tissue proper. They secrete the fibres and the ground substance. Most of the cells seen in connective tissue proper will be these. They are often almost 2 dimensional (flat and wide) Connective Tissue: Ocular examples 31 Cells  Fibroblasts: This is the fundamental cell type of connective tissue proper. They secrete the fibres and the ground substance. Most of the cells seen in connective tissue proper will be these. They are often almost 1. epithelium 2 dimensional (flat and wide) 2. Bowman’s layer Can be seen in the stroma of the cornea (appearing as dark patches sandwiched between lighter areas of tightly packed 3. stroma collagen fibres) 4. Descemet’s membrane 5. endothelium Connective Tissue 32 Cells  Fibroblasts: This is the fundamental cell type of connective tissue proper. They secrete the fibres and the ground substance. Most of the cells seen in connective tissue proper will be these. They are often almost 2 dimensional (flat and wide)  Other, less numerous cells. Many derived from white blood cells: Plasma cells – produce antibodies Macrophages – phagocytosis Mast cells – produce histamine & heparine for the inflammatory response Connective Tissue 33 Types of connective tissue There are two basic types of connective tissue: 1. Specialist connective tissue Cartilage, blood, bone, etc. Connective Tissue: Ocular examples 34 Types of connective tissue There are two basic types of connective tissue: 1. Specialist connective tissue Cartilage, blood, bone, etc. The orbit E.g., the orbit of the eye is made up of 7 bones: The 3 major bones of the face (frontal, zygomatic & maxillary). The ethmoid, lacrimal, great wing of sphenoid, lesser wing of sphenoid Connective Tissue: Ocular examples 35 Types of connective tissue There are two basic types of connective tissue: 1. Specialist connective tissue Cartilage, blood, bone, etc. E.g., the orbit of the eye is made up of 7 bones: The 3 major bones of the face (frontal, zygomatic & maxillary). The ethmoid, lacrimal, great wing of sphenoid, lesser wing of sphenoid E.g., the sclera of many vertebrates is reinforced by a ring of cartilage (though not in mammals!) Connective Tissue 36 Types of connective tissue There are two basic types of connective tissue: 1. Specialist connective tissue Cartilage, blood, bone, etc. 2. Connective tissue proper – we shall consider only this today a. Loose (fibres loosely arranged) i. Aereolar ii. Adipose b. Dense (fibres densely arranged) i. Regular ii. Irregular Connective Tissue 37 Loose aereolar connective tissue proper  Think of this as the packing material of the body  Aereolar connective tissue is soft and pliable, and is the most widely distributed type of connective tissue.  It traps fluid (causing, for example, bruising), amongst a host of other functions (supporting, binding, protecting, storing nutrients, etc.) Light micrograph Note all the empty space between the loosely packed. Areola meaning "a small open space“. Electron micrograph Connective Tissue: Ocular examples 38 Loose aereolar connective tissue proper  Think of this as the packing material of the body  Aereolar connective tissue is soft and pliable, and is the most widely distributed type of connective tissue  It traps fluid (causing, for example, bruising), amongst a host of other functions (supporting, binding, protecting, storing nutrients, etc.)  The stroma (body) of the iris is a good example of a loose aereolar connective tissue. This allows it to change shape easily to control pupil size Connective Tissue 39 Loose adipose (fat) connective tissue proper  Like areolar tissue in structure, but its nutrient-storing ability is much greater  Unlike most types of connective tissue as it is largely made up of fat cells (adipocytes). These appear as white spaces, as all organelles have been pushed to the side and virtually the whole cell is occupied by a fat droplet  Constitutes 18% of an average person’s body weight  Adipose tissue may develop almost anywhere areolar tissue is plentiful, but it usually accumulates under the skin, where it acts as a shock absorber, as insulation, and as an energy storage site Connective Tissue: Ocular examples 40 Loose adipose (fat) connective tissue proper Adipose tissue (fat)  Adipose tissue fills most of the orbital cavity, surrounding the eyeball, muscles, nerves, & blood vessels  Provides a helpful cushion to protect against trauma  Decreases in the elderly, potentially leading to enophthalmos (eye sinking into the orbit) Connective Tissue: Ocular examples 41 Loose adipose (fat) connective tissue proper  Adipose tissue fills most of the orbital cavity, surrounding the eyeball, muscles, nerves, & blood vessels  Provides a helpful cushion to protect against trauma  Decreases in the elderly, potentially leading to enophthalmos (eye sinking into the orbit)  Adipose tissue also surrounds the lacrimal gland (& excessive amounts are associated with an autoimmune disorders called Sjögren’s syndrome; for reasons unknown) adipocyte Light micrograph Connective Tissue 42 Dense regular connective tissue proper  Dense connective tissue is highly Collagen fibrous (sometimes just called fibrous fibres connective tissue)  Regular DCT contains closely packed bundles of collagen fibres, all running in the same direction.  This confers enormous tensile strength (resistance to pulling in a single direction).  Ideal for tendons (attaching muscles to bone), and ligaments (binding bones together) Connective Tissue: Ocular examples 43 Dense regular connective tissue proper 1. epithelium 2. Bowman’s layer  In the eye, a good example of a regular DCT is the corneal stroma (body)  Here, the collagen fibres are arranged in ~250 3. stroma sheets (“lamellae”), each ~ 2µm thick and runing parallel to the corneal surface  The fibres within each lamella are oriented in the same direction as one another, but at right angles to those of adjacent lamellae 4. Descemet’s membrane  The result: a tough, unyielding, and crucially 5. endothelium transparent substance  Keratoconus is a condition caused by disorganised lamellae, leading to a misshapen cornea Connective Tissue 44 Dense irregular connective tissue proper  The same basic elements as regular Collagen fibres DCT, but the bundles of collagen fibres are much thicker and run in all directions (irregularly arranged)  This confers strength in all directions  Useful in skin, and for surrounding certain internal organs (e.g., kidney, muscles, bones, etc.) Connective Tissue: Ocular examples 45 Dense irregular connective tissue proper  The same basic elements as regular DCT, but the bundles of collagen fibres are much thicker and run in all directions (irregularly arranged)  This confers strength in all directions  Found in the sclera (white of the eye), which maintains the overall shape the eyeball by offering resistance to a variety internal and external forces…  …and which due to its irregularly arranged fibres is opaque (in contrast to the regularly arranged connective tissue of the cornea) Electron micrograph Connective Tissue 46 Connective tissue highlights Connective Tissue  All connective tissue composed of: 1. Ground substance Specialist (not Extracellular matrix Proper 2. Fibres discussed) 3. Cells  Connective tissue divided into proper & Loose Dense various specialist tissues  Proper divided into loose & dense  Loose divided into aereolar & adipose Aereolar Regular  Dense divided into regular & irregular Adipose Irregular OV1113: Tissue Types ▪ Overview: The 4 types of tissue and their roles ▪ Nervous tissue ▪ Muscle tissue ▪ Connective tissue Proper connective tissue ▪ Epithelial tissue Covering epithelia Glandular epithelia 47 Epithelial Tissue 48 Overview  Epithelia form boundaries between different environments Without epithelia we’d not only be soup, but we wouldn’t even have any nice lumps. We’d be a textureless soup like tomato soup, which is the worst soup Epithelial Tissue 49 Overview  Epithelia form boundaries between different environments  As we shall see in this lecture and throughout the course, these boundaries can serve multiple roles Epithelial Tissue 50 Overview  Epithelia form boundaries between different environments  As we shall see in this lecture and throughout the course, these boundaries can serve multiple roles  Epithelia come in two main forms: Covering epithelia, that line the surfaces of the outer body and internal organs Glandular epithelia, that form the various glands of the body OV1113: Tissue Types ▪ Overview: The 4 types of tissue and their roles ▪ Nervous tissue ▪ Muscle tissue ▪ Connective tissue Proper connective tissue ▪ Epithelial tissue Covering epithelia Glandular epithelia 51 Epithelial Tissue: Covering epithelia 52 Covering epithelia overview  Line the free surfaces of the body  Can be thought of a bit like the membrane of a cell  And like membranes can have many functions: Protection (e.g., skin) Absorption (e.g., digestive track) Sensation (e.g., taste, smell, etc.)  Epithelial cells are usually polyhedral (often hexagonal) in shape, with strong attachments between adjacent cells (tight junctions)  Most epithelial tissue is highly regenerative, innervated (supplied by sensory and motor nerve fibres), and avascular (contains no blood vessels) Epithelial Tissue: Covering epithelia 53 Covering epithelia overview  All epithelial sheets rest on a basement Apical surface membrane, that reinforces the epithelia and helps it resist stretching and tearing  We call the side of the epithelium that rests on the basement membrane, the basal surface  We call the other, free side of the epithlium, the apical surface Basal surface Epithelial Tissue: Covering epithelia 54 Covering epithelia overview microvilli  All epithelial sheets rest on a basement membrane, that reinforces the epithelia and helps it resist stretching and tearing  We call the side of the epithelium that rests on the basement membrane, the basal surface  We call the other, free side of the epithlium, cilia the apical surface  Some apical surface are smooth, but most are covered with microvilli (little “fingers” that increase surface area – important for absorption & secretion), or cilia (hairs that are important for intercellular signalling, movement, and sensation – e.g., hearing) Epithelial Tissue: Covering epithelia 55 Types of epithelia  Covering epithelia are classified based Squamous (flat) cornea on the shape of the cells and by the number of layers  Three primary types of shape: squamous, cuboidal, columnar Cuboidal kidney  The 3 shapes don’t have simple/ clearly defined roles (e.g., all 3 are capable of secreting and absorbing, Columnar and all 3 can be protective when stratified)…  …though as we’ll see squamous cells Gall bladder are often used for protective coatings Epithelial Tissue: Covering epithelia 56 Types of epithelia  Covering epithelia are classified based on the shape of the cells and by the number of layers  Three primary types of shape: squamous, cuboidal, columnar  In practice, you will rarely be able to see the cell membrane in histological sections…  …but you can usually infer the shape of the cell, as it is mirrored in the shape of the nucleus squamous cuboidal columnar Epithelial Tissue: Covering epithelia 57 Types of epithelia  Covering epithelia are classified based on the shape of the cells and by the number of layers  Two types of layers: simple (one layer) or stratified (multiple layers) Simple Stratified Epithelial Tissue: Covering epithelia 58 Types of epithelia  Covering epithelia are classified based on the shape of the cells and by the number of layers  Two types of layers: simple (one layer) or stratified (multiple layers) Lining of blood vessels  Simple epithelia are useful when an exchange of substances is required The alveoli of the lungs Epithelial Tissue: Covering epithelia: Ocular examples 59 1. epithelium Types of epithelia 2. Bowman’s layer  A good ocular example of a single layered epithelia is the basal (inner) surface of the cornea (the corneal 3. stroma endothelium)  This allows the cornea to exchange substances with the aqueous below The corneal endothelium: (nutrients go up, waste goes down) A simple squamous epithelium 4. Descemet’s membrane 5. endothelium 3 4 5 Epithelial Tissue: Covering epithelia 60 Types of epithelia  Covering epithelia are classified based on the shape of the cells and by the number of layers Stratified  Two types of layers: simple (one squamous layer) or stratified (multiple layers) epithelium  Simple epithelia are useful when an exchange of substances is required  Stratified epithelia are for protection, Skin (an organ, and are always found in areas subject made up of to abrasion (e.g., skin, cornea, vagina) multiple tissues) Epithelial Tissue: Covering epithelia 61 Types of epithelia  Covering epithelia are classified based on the shape of the cells and by the number of layers  Two types of layers: simple (one layer) or stratified (multiple layers)  Simple epithelia are useful when an exchange of substances is required  Stratified epithelia are for protection, and are always found in areas subject to abrasion (e.g., skin, cornea, vagina)  Stratified epithelia are usually squamous in humans Epithelial Tissue: Covering epithelia: Ocular examples 62 1. epithelium Types of epithelia 2. Bowman’s layer  A good ocular example of a stratified squamous epithelia is the apical (outer) surface of the cornea 3. stroma (the corneal epithelium)  This protects the cornea from dirt, eyelids, clumsy optometrists 4. Descemet’s membrane 5. endothelium The corneal epithelium: 1 A stratified squamous epithelium 2 Epithelial Tissue: Covering epithelia 63 Types of epithelia  Covering epithelia are classified based on the shape of the cells and by the number of layers  Two types of layers: simple (one layer) or stratified (multiple layers)  With stratified tissue, the shape may change across layers…  …by convention the apical (surface) layer is used when naming the tissue Epithelial Tissue: Covering epithelia 64 Types of epithelia  Covering epithelia are classified based on the shape of the cells and by the number of layers  Two types of layers: simple (one layer) or stratified (multiple layers)  Three primary types of shape: squamous, cuboidal, columnar  Combined, 2 x 3 = … 8? Epithelial Tissue: Covering epithelia 65 Types of epithelia Trachea  Covering epithelia are classified based on the shape of the cells and by the number of layers  Two types of layers: simple (one layer) or stratified (multiple layers)  Three primary types of shape: squamous, cuboidal, columnar  Combined, 2 x 3 = … 8?  Also pseudo-stratified (simple columnar epithelia that look stratified) Cells are different shapes, giving stratified appearance, but on close inspection all are sitting on the basement membrane Epithelial Tissue: Covering epithelia 66 bladder empty & relaxed Types of epithelia (transitional cells not stretched & cuboidal)  Covering epithelia are classified based on the shape of the cells and by the number of layers  Two types of layers: simple (one layer) or stratified (multiple layers)  Three primary types of shape: squamous, cuboidal, columnar  Combined, 2 x 3 = … 8?  Also pseudo-stratified (simple columnar epithelia that look stratified)  And transitional (cells that are round in shape when the organ is relaxed, but bladder full & distended flatten when distended) (transitional cells stretched squamous) Epithelial Tissue: Covering epithelia 67 Covering epithelia highlights  There are 8 basic types of covering epithelia  3 basic shapes: squamous, cuboidal, columnar Histologically, cell shape can be inferred from the shape of the nucleus  Stratified epithelia: Multi-layered and named according to the shape of the surface layer of cells Often serve protective functions: found in areas subject to abrasion (e.g. outer surface of cornea or skin) The bladder wall is coated with transitional epithelium, whose shape can change  Simple epithelia: Good for exchange of substances Found, e.g., lining blood vessels, the alveoli of the lungs, and the inner surface of the cornea Epithelial Tissue: Covering epithelia 68 Covering epithelia: Advanced topic: Keratinized epithelia  Although stratified epithelia are often used for protection, epithelial cells are “moist”  As a result, they are relatively weak, and permeable to water  In skin, the apical (surface) layers are actually composed of dead squamous cells, filled with the protein keratin (replacing the normal protoplasm of the cell)  This makes it dry, impervious to water, and an even more effective barrier against abrasions Epithelial Tissue: Covering epithelia 69 Covering epithelia: Advanced topic: Keratinized epithelia  Trapped deposits of keratin can cause milia around the eye (small white cysts)  Harmless, but can cause scarring if attempt to pop (can be treated by clearing out the pores to release the keratin build- up) Epithelial Tissue: Covering epithelia 70 Covering epithelia: Advanced topic: Melanin  In skin, the basal (bottom) layers contain the pigment melanin  This accounts for variations in skin colour Epithelial Tissue: Covering epithelia: Ocular examples 71 Covering epithelia: Advanced topic: Melanin  In skin, the basal (bottom) layers contain the pigment melanin  This accounts for variations in skin colour  Many of the epithelia lining the inside of the eye are also pigmented with melanin  This serves to absorb stray light and improve image quality (the black box effect) Choroid & retina Posterior iris Surface of ciliary body Epithelial Tissue: Covering epithelia 72 Epithelial tissue in the news OV1113: Tissue Types ▪ Overview: The 4 types of tissue and their roles ▪ Nervous tissue ▪ Muscle tissue ▪ Connective tissue Proper connective tissue ▪ Epithelial tissue Covering epithelia Glandular epithelia 73 Epithelial Tissue: Glandular epithelia 74 Glandular epithelium overview  Glandular epithelial cells form the various glands of the body: a gland being a group of cells that make and secrete a particular product (often an aqueous fluid containing proteins, lipids, or steroids)  Glandular epithelial tissue is involved in the production and release of many different secretory products, such as sweat, saliva, breast milk, digestive enzymes, and hormones, among many other substances (This is not a comprehensive list) Epithelial Tissue: Glandular epithelia 75 Types of glandular secretion  Three main types of cellular composition: 1. Serous – a watery substance, often containing proteins (e.g., saliva in the mouth) 2. Mucous – a thick, sticky substance (e.g., in the larynx) 3. Sebaceous – an oily substance (e.g., in the armpit)  Cell types can be differentiated histologically as well. Mucous cells typically stain lighter than their serous counterparts when stained  Most glands produce only one type of secretion. Some, however, such as the Mucous (light) granules lacrimal gland show here, are mixed… Serous (darker) secretions Epithelial Tissue: Glandular epithelia 76 Types of glandular secretion  …what’s more multiple glands may work together within an organ:  E.g., the tear film is comprised of mucous (from goblet cells et al), serous fluid (from lacrimal gland et al), and sebaceous fluid produced (from meibomian gland et al) Epithelial Tissue: Glandular epithelia 77 Types of glandular secretion  …what’s more multiple glands may work together within an organ:  E.g., the tear film is comprised of mucous (from goblet cells et al), serous fluid (from lacrimal gland et al), and sebaceous fluid produced (from meibomian gland et al) Epithelial Tissue: Glandular epithelia 78 Glands can be endocrine or exocrine  Exocrine glands secrete their product onto the epithelial surface (e.g., the skin surface, or into the cavities of internal organs)  Endocrine secrete hormones into the interstitial fluid, where they go on to enter the blood Epithelial Tissue: Glandular epithelia 79 Endocrine glands  Structurally diverse. Most are multicellular organs, but some individual hormone-producing cells are scattered throughout the digestive tract lining (mucosa) and in the brain  Generally ductless  Their secretions are varied (amino acids, peptides, glycoproteins, steroids)  Not all endocrine glands arise from epithelial tissue, so we’ll not discuss them more in a later lecture on the endocrine system Epithelial Tissue: Glandular epithelia 80 Exocrine glands  In multicellular exocrine glands, secretions travel up to the surface via a series of connecting cells that form a duct  Alternatively, unicellular exocrine glands exist, in which a single cell produces and secretes  Over the next few slides we’ll look at some examples of each Epithelial Tissue: Glandular epithelia 81 Unicellular exocrine glands  Most common example is the mucus secreting goblet cell Note the triangular nucleus Electron micrograph Epithelial Tissue: Glandular epithelia 82 Unicellular exocrine glands  Most common example is the mucus secreting goblet cell  Found in the epithelium of the trachea and the digestive tube (to protect/lubricate) Epithelial Tissue: Glandular epithelia 83 Unicellular exocrine glands: Ocular examples  Most common example is the mucus secreting goblet cell  Found in the epithelium of the trachea and the digestive tube (to protect/lubricate)  Also numerous in the conjunctiva of the eye…  …where they help form the mucous layer of the tear film Epithelial Tissue: Glandular epithelia 84 Unicellular exocrine glands: Ocular examples  Most common example is the mucus secreting goblet cell  Found in the epithelium of the trachea and the digestive tube (to protect/lubricate)  Also numerous in the conjunctiva of the eye…  …where they help form the mucous layer of the tear film  Distributed across the eye, but most dense nasally (N) Epithelial Tissue: Glandular epithelia 85 Multicellular exocrine glands  Consist of groups of secretory cells, connected to a free surface by ducts (also composed of epithelial cells) Epithelial Tissue: Glandular epithelia 86 Multicellular exocrine glands  Consist of groups of secretory cells, connected to a free surface by ducts (also composed of epithelial cells)  Formed through invagination (inward growth) of an epithelial sheet Epithelial sheet Epithelial Tissue: Glandular epithelia 87 Multicellular exocrine glands  If only a single duct, called simple  If multiple ducts, called compound Epithelial Tissue: Glandular epithelia 88 Simple multicellular exocrine glands  A good example is the meibomian (or: “tarsal”) gland of the eyelid Epithelial Tissue: Glandular epithelia 89 Simple multicellular exocrine glands  A good example is the meibomian (or: “tarsal”) gland of the eyelid  See for yourself! (or don’t) Epithelial Tissue: Glandular epithelia 90 Compound multicellular exocrine glands  A good example is the lacrimal gland of the eyelid Electron micrograph Epithelial Tissue: Glandular epithelia 91 Multicellular exocrine glands  Can also be classified based on the shape of their secretory units:  Tubular, if secretory units form T A tubes T A T  Alveolar (or: “acinar”) if secretory T A units form small hollow cavities  Can also be a bit of both: tubuloalveaolar A T TA Epithelial Tissue: Glandular epithelia 92 Quiz: Colon gland from the digestive tract?  Multicellular not unicellular)  Simple not compound (one duct)  Tubular not alveolar (secretory unit tube shaped)  “I spy some multicellular simple tubular glandular epithelial tissue” (!) Epithelial Tissue: Glandular epithelia 93 Quiz: Meibomian gland of the eyelid?  Multicellular not unicellular  Simple not compound (one duct)  Alveolar not tubular (secretory units sac shaped)  “I spy some multicellular simple alveolar glandular epithelial tissue” (!) Epithelial Tissue: Glandular epithelia 94 Quiz: Lacrimal gland of the eyelid?  Multicellular not unicellular  Compound not simple (multiple duct)  Alveolar not tubular (secretory units sac shaped)  “I spy some multicellular compound alveolar glandular epithelial tissue” (!) Electron micrograph Epithelial Tissue: Glandular epithelia Multicellular exocrine glands Merocrine  Can also be classified based on their mode of secretion: Holocrine  Merocrine, if product is released via exocytosis recall: exocytosis is a form of active transport in which vesicles fuse with the cellular membrane, releasing contents to the extracellular space) E.g., sweat gland, salivary gland  Holocrine, if whole cell ruptures to release product E.g., sebaceous skin glands  Apocrine, tip of cell is shed and cell repairs the Apocrine damage No known examples in humans? Epithelial Tissue: Glandular epithelia 96 Glandular epithelia highlights  Glands can be classified in term of: 1. Where they release their product 3. Method of secretion Endocrine  Secretion into bloodstream Merocrine  secreted via exocytosis Exocrine  Secretion into ducts Holocrine  whole cell ruptures Apocrine  tip of cell is shed 2. How many cells they contain 4. Type of secretion Unicellular (one cell produces and Serous  watery substance secretes; e.g., goblet cells) e.g., mouth Multicellular (multiple cells work together Mucous  thick, sticky substance to produce & secrete) e.g., throat i. Simple (one duct) vs Compound (multiple Sebaceous  oily substance ducts) e.g., armpit ii. Tubular vs. Alveolar (or both: tubuloalveolar) OV1113: Tissue Types ▪ Overview: The 4 types of tissue and their roles ▪ Nervous tissue ▪ Muscle tissue ▪ Connective tissue Proper connective tissue ▪ Epithelial tissue Covering epithelia Glandular epithelia 97  Further Reading  [Overview] Chapter 4 of Marieb & Hoehn (20XX). Human Anatomy and Physiology City, University of London Northampton Square London EC1V 0HB United Kingdom T: +44 (0)20 7040 5060 E: [email protected] W: https://www.city.ac.uk/people/academics/peter-jones