Anatomy of the Eye

The Eye

• Conjunctiva: A thin, transparent membrane.
• Cornea: The transparent front part of the eye.
• Iris: The colored part of the eye; controls the amount of light entering by adjusting the pupil size.
• Lens: Changes shape to focus on objects at varying distances.
• Pupil: A gap in the center of the iris that allows light to enter the eye.
• Aqueous Humor: Fluid-filled space between the cornea and the lens.
• Vitreous Humor: Transparent, jelly-like substance that maintains the eye's shape.
• Suspensory Ligaments: Connect ciliary muscles to the lens and change the shape of the lens.
• Retina: The light-sensitive lining at the back of the eye; it converts light into electrical signals.
• Sclerotic Layer: The tough, white outer layer of the eye; it provides protection, structure to the eyeball, and an attachment point for muscles.
• Choroid: Layer between the sclerotic layer and the retina, containing blood vessels, giving oxygen and nutrients to the retina. It absorbs excess light and is black in color.
• Fovea: Area of the retina needed for sharp central vision with a high concentration of cone cells for color vision.
• Optic Nerve: Carries electrical signals from the retina to the brain.
• Blind Spot: Area with no rods or cones, resulting in no image detection in this area.
• Ciliary Muscles: Fibers that hold and change the shape of the lens.

The Ear

• Pinna: Funnel that captures sound waves, directing them into the ear.
• Auditory Canal: Tunnel that carries sound waves from the outer ear to the eardrum.
• Eardrum (Tympanic Membrane): Membrane that vibrates when hit by sound waves, amplifying the sound.
• Ossicles (Malleus, Incus, Stapes): Tiny bones that amplify the eardrum's vibrations, transferring them to the inner ear. The Stapes focuses the vibrations at oval window, increasing the intensity.
• Oval Window: Membrane that receives amplified vibrations from the ossicles, transmitting them into the fluid-filled cochlea.
• Eustachian Tube: Canal that connects the middle ear to the throat, regulating air pressure to keep the eardrum balanced.
• Semicircular Canals: Network of curved, fluid-filled tubes that detect head movement, aiding in balance and stability.
• Vestibular Nerve: Pathway that carries balance signals from the semicircular canals to the brain.
• Cochlea: Snail-shaped organ with fluid and sensory hair cells that convert vibrations into electrical signals for the brain to process as sound.
• Auditory Nerve: Nerve that carries sound signals from the cochlea to the brain.

The Skin

• Epidermis: Outer Layer
  • Layer of dead skin: Outer protective layer, preventing water loss and infection.
  • Pores: Allow the release of sweat and sebum.
  • Light Contact Receptor: Detects light touch and textures, found in the basal layer of the epidermis.
• Dermis: Middle Layer
  • Receptors for heat, cold, pain, pressure, hair movement, and light contact.
  • Hair: Grows in the dermis, providing protection and sensation.
  • Sweat Glands: Produce sweat to regulate body temperature.
  • Sebaceous Glands: Produce oil (sebum) to keep the skin and hair moisturized.
• Hypodermis: Innermost Layer
  • Hair Movement Receptors: Detect deep touch and vibrations. Some receptors extend into this layer.
  • Fat and Connective Tissue: Provides insulation, cushioning, and energy storage.
  • Tendon: Connective tissue that attaches muscle to bone.
  • Olfactory cells: nerve cells in the nose that are transferred to the brain.

Nervous System

• Central Nervous System (CNS): Consists of the brain and spinal cord.
• Peripheral Nervous System (PNS): Consists of nerves (spinal, cranial) and ganglia. Ganglia are lumps attached to nerves containing somas (cell body) of neuron.
• Afferent Neurons: Carry sensory information from the periphery to the CNS.
• Efferent Neurons: Carry motor commands from the CNS to the periphery.
• Somatic Nervous System: VOLUNTARY; part of the peripheral nervous system
• Automatic Nervous System: INVOLUNTARY; part of the peripheral nervous system
• Both somatic and autonomic nervous systems use afferent and efferent pathways.

Endocrine System

• The body uses hormones instead of electrical impulses when a slower response is needed.
• Hormones regulate:
  • Storage of glucose.
  • Growth and development.
  • Metabolism and homeostasis.
• Hormones transport through the bloodstream to target cells, which respond to a specific hormone.
• Hormones recognize specific receptor shapes.

Major Endocrine Organs

• Pituitary Gland (Master Gland): Links the nervous and endocrine systems, controls other glands by releasing regulatory hormones and located at the base of the brain.
• Thyroid Gland: Produces thyroxine, regulating metabolism, energy levels, and growth.
• Pancreas: Produces insulin and glucagon, which regulate blood sugar levels.
• Adrenal Glands: Release adrenaline, on top of kidneys.
• Ovaries & Testes: Produce sex hormones oestrogen and testosterone.

Diseases

• Virus: Needs a host to survive and reproduces only within cells.
  • Virions: Fully developed virus particles composed of DNA or RNA but never both, surrounded by a capsid (protein coat).
• Agent: Anything that causes disease.
• Host: Organism affected by an agent.
• Vector: Organism that carries an agent/pathogen and transmits it to a host, but is not affected by it.
• Smallest to Largest: Virus, protozoa, bacteria, fungi.

Diabetes

• Caused by improper function of the hormone insulin secreted by the pancreas, causing high blood glucose levels
• Type I: caused by the pancreas dysfunction.
• Type II: lifestyle, diet, genetics
• Other: Diabetes caused by medication
• Insulin: Released when blood glucose levels are too high, causing glucose to be taken up by cells.
• Glucagon: Released when blood glucose levels are too low, releasing stored glucose from the liver.
• Normal blood glucose level: 80-100 milligram glucose per 100 milliliter of blood.

Regions of the Brain

• Three main regions: Cerebrum, Cerebellum, Brain Stem, Diencephalon

Cerebrum

• Responsible for complex actions such as speech and reasoning.
• Largest part of the brain, divided into left and right hemispheres.
• Surface has raised ridges called gyri and grooves called sulci.
• Four Lobes:
  • Frontal Lobe: Reasoning, problem-solving, and voluntary movements.
  • Parietal Lobe: Processes sensory information such as touch and spatial awareness.
  • Occipital Lobe: Responsible for visual processing.
  • Temporal Lobe: Processes auditory information and memory.
  • Corpus Callosum: Connects the two hemispheres of the cerebrum.

Cerebellum

• Balance and coordination.
• Contains white matter in a tree-like structure called the arbor vitae.

Brain Stem

• Autonomic functions, communication link between the brain and rest of body.
• Three main parts:
  • Medulla Oblongata: Controls breathing and heart rate.
  • Pons: Link for communication between brain regions; involved in sleep cycles, respiratory functions, and motor control.
  • Midbrain: Processes visual and auditory data
    • Superior Colliculus (part of the midbrain): Body orientation and eye movements.
  • Pineal Gland: Regulates sleep cycles.

Diencephalon

• Processes sensory information and controls autonomic functions.
• Located between the corpus callosum and the midbrain.
• Two major components:
  • Thalamus: Acts as the main relay station for sensory information.
  • Hypothalamus: Maintains homeostasis and directs hormone release, regulating metabolism, water balance, temperature, and hunger; connects to the pituitary gland to direct hormone release.

Brain Function Identification

• Sleep cycles (gland): Pineal Gland
• Reasoning: Frontal Lobe
• Balance and coordination: Cerebellum
• Connecting left and right hemispheres: Corpus Callosum
• Visual and auditory data processing: Midbrain
• Regulation of breathing and heart rate: Medulla Oblongata
• Maintaining homeostasis by directing the pituitary: Hypothalamus
• Body orientation and eye movements: Superior Colliculus
• Relays information to the correct area of the brain: Thalamus
• Regulates sleep cycles, respiratory processes, and motor control: Pons

Lines of Defence

First

• part of the innate immune system, consisting of physical and chemical barriers
• Physical:
  • Skin
  • Mucous
• Chemical barriers:
  • Tears and saliva (slight acidity)
  • Stomach acid
  • Sweat and sebum

Second

• The complement system: a group of proteins that destroy pathogens and promotes inflammation
  • 3 main roles: Phagocytosis, attracting macrophages and neutrophils to the infection site, and rupturing the membranes of foreign calls.
• Neutrophils: Abundant white blood cells that are the first responders to infection. They destroy pathogens through phagocytosis and release enzymes that kill bacteria.
• Macrophages: Large phagocytic cells that engulf and digest microbes, dead cells, and debris, found in tissues
• Eosinophils: White blood cells that kill parasites and are involved in allergic reactions. They release toxic granules and contribute to inflammation. High eosinophil levels are associated with allergies and asthma.
• Basophils: Rarest type of white blood cell, involved in allergic and inflammatory responses, attract other immune cells to the site of infection.
• Mast Cells: Found in tissues, especially near blood vessels, play a key role in allergic reactions, releasing histamine and other chemicals that trigger inflammation and help defend against parasites, also involved in wound healing and immune tolerance.
• Dendritic Cells: Messengers between the innate and adaptive immune systems, found in tissues that are in contact with the external environment
• Lymphatic System: Consists of vessels, nodes, and organs that transport lymph (fluid containing white blood cells), removes waste, excess fluids, and facilitates immune responses by transporting pathogens to lymph nodes where they can be destroyed.
• Spleen: Filters blood, removes old red blood cells, and fights infections. It contains white blood cells that detect and destroy pathogens, making it a key part of the immune system.
• Stages of Phagocytosis:
  • Attachment: The phagocyte recognizes and binds to the pathogen using receptors.
  • Engulfment: The phagocyte surrounds the pathogen with its membrane, forming a vesicle called a phagosome.
  • Fusion with Lysosome: The phagosome merges with a lysosome, forming a phagolysosome.
  • Destruction: Enzymes and toxic molecules in the lysosome break down the pathogen.
  • Exocytosis: The waste products are expelled from the cell.