Module 14: Eye Anatomy

• The following points pertain to Module 14: Special Senses

Eye Anatomy

• The eye has specific muscles for movement: superior rectus, medial rectus, inferior rectus, lateral rectus, superior oblique, and inferior oblique.
• The lacrimal apparatus is located above the lateral end of the eye.
• The lacrimal apparatus consists of the lacrimal duct and gland and releases tears onto the anterior eye surface, which then drain into the nasal cavity.
• Lacrimal secretions contain antibodies and lysozyme, which help to cleanse, moisten, and protect the eye from infection.
• The outermost fibrous layer contains the cornea, which is well-supplied with nerve endings and considered the "window" of the eye for light entry.
• The sclera is a thick, protective connective tissue known as the "white of the eye."
• The middle-vascular layer contains the choroid, a blood-rich tunic with dark pigment that prevents light scattering.
• The ciliary body is a smooth muscle structure attaching to the lens.
• The iris dilates and constricts to control pupil size.
• The pupil is the opening in the iris.

Retina Layers

• The sensory tunic of the eye has two layers: an outer pigmented layer and an inner transparent layer.
• The outer pigmented layer absorbs light and prevents light scattering; it also phagocytizes receptor cells and stores vitamin A.
• The inner transparent layer is a neural layer that contains cells specialized for visual processing, including rods and cones.
• Rods are concentrated at the retina's periphery and are specialized for processing gray tones in dim light.
• Cones are concentrated at the retina's center and are responsible for color vision.
• The optic disc is the blind spot where electrical signals leave the eye en route to the cerebral cortex.
• The fovea centralis is the region of the retina with the highest concentration of cones, providing the greatest visual acuity.
• Aqueous humor is located posterior to the cornea and anterior to the lens.
• Vitreous humor is located posterior to the lens and anterior to the retina.
• Glaucoma occurs if these fluids are not adequately drained, putting pressure on the retina.

Visual Pathway

• Visual information travels from the optic nerve to the optic chiasm, then via optic tracts to the lateral geniculate nucleus, and finally to the primary visual cortex.

Ear Anatomy

• External ear structures include the auricle, external auditory meatus, and tympanic membrane.
• Middle ear structures include the tympanic cavity and auditory ossicles, which transmit sound waves from the outer ear to the fluid-filled inner ear.
• The oval window is where the stapes vibrates against, transferring sound waves to the inner ear fluids.
• Inner ear structures include the cochlea, semicircular canals, and vestibule.

Endocrine System

• The following information pertains to Module 15: Endocrine System

Steroid Classifications

• Steroids are lipophilic, utilize plasma along with cytosolic and nuclear receptors, and are categorized as Endocrine producing Estrogen
• Peptides can be lipophilic, using cytosolic and nuclear receptors, and are categorized as Endocrine while producing Thyroxine
• Peptides can be hydrophilic, use plasma receptors and are categorized as Endocrine, with ACTH production
• Proteins are hydrophilic, use plasma receptors and are categorized as Endocrine and produce GH
• Amino Acid Derivatives are hydrophilic, use plasma receptors, are categorized as Endocrine and produce Epinephrine.

Hypothalamic Hormones

• Thyrotropin-releasing hormone (TRH) is produced by parvocellular cells in the paraventricular nucleus and stimulates TSH and prolactin release.
• Corticotropin-releasing hormone (CRH) is produced by parvocellular cells in the paraventricular nucleus and stimulates ACTH release.
• Growth hormone-releasing hormone (GHRH) is produced by neuroendocrine cells in the arcuate nucleus and stimulates GH release.
• Gonadotropin-releasing hormone (GnRH) is produced by neuroendocrine cells in the preoptic area and stimulates FSH and LH release.
• Prolactin-inhibitory hormone (PIH or dopamine) is produced by neuroendocrine cells in the arcuate nucleus and inhibits prolactin release.
• Growth hormone-inhibitory hormone (GIRH, Somatostatin) is produced by neuroendocrine cells in the periventricular nucleus and inhibits GH and TSH release.

Anterior Pituitary Hormones

• Growth Hormone (GH) target tissue is most tissues of the body and it increases muscle mass, decreases body fat, and affects protein, lipid and carbohydrate metabolism.
• Thyroid Stimulating Hormone (TSH) target tissue is the thyroid gland and it stimulates release of T3/T4 from the thyroid gland.
• Adrenocorticotropic Hormone (ACTH) target tissue is the adrenal cortex and it cauess synthesis of steroids by cortical cells in the adrenal gland.
• Prolactin (PRL) target tissue is the mammary glands and it plays an important role in fluid balance, most notably in milk production in the mammary gland.
• Follicle Stimulating Hormone (FSH) / Luteinizing Hormone (LH) target tissue is Gonads (testes and ovaries) and promotes the growth and function of the gonads.

Posterior Pituitary Hormones

• Oxytocin's target tissue is the uterus and mammary glands functioning in Uterine contractions and Milk ejection.
• Antidiuretic Hormone (ADH) target tissue is the kidneys functioning in Water reabsorption.

Actions of Insulin vs. Glucagon

• Insulin stimulates glucose uptake, utilization, and storage, and stimulates hepatocytes to convert glucose into glycogen, while also decreasing lipolysis, and inreasing amino acids.
• Glucagon stimulates liver glycogen breakdown and gluconeogenesis, while increasing lipolysis, and stimulating glucose release by heptocytes.

Blood Elements

• The following points refer to Module 9: Blood elements

Leukocyte Subcategories

• Neutrophils account for 50-70% of leukocytes.
• Lymphocytes account for 25-40% of leukocytes.
• Monocytes account for 4-8% of leukocytes.
• Eosinophils account for 2-4% of leukocytes.
• Basophils account for less than 1% of leukocytes.

Formed elements

• Erythrocytes (red blood cells) appear as flattened biconcave disks, lacking a nucleus, and appear pale red in standard blood smears.
• Leukocytes (white blood cells) are divided into granulocytes and agranulocytes.
• Granulocytes have abundant granules in their cytoplasm and a lobed nucleus.
• Neutrophils' nuclear lobes increase with age, and they have pale lilac granules.
• Eosinophils generally have a two-lobed nucleus and bright red-orange granules.
• Basophils' nucleus is generally two-lobed but hard to see due to heavy, dense, dark purple granules.
• Agranulocytes lack abundant granules in the cytoplasm
• Lymphocytes are spherical cells with a single, often large, nucleus occupying much of the cell's volume.
• Monocytes are the largest leukocyte, with an indented or horseshoe-shaped nucleus.
• Platelets are cellular fragments surrounded by a plasma membrane and contain granules, staining purple.