A★

Study Guide Final

Special Senses

Accessory Structures, Cornea, Lens, and Humors of the Eye

  • Accessory Structures: These include the eyelids, eyelashes, eyebrows, lacrimal apparatus, and extrinsic eye muscles. They provide protection, lubrication, and movement for the eye.
  • Cornea: The transparent outer layer of the eye that helps focus light as it enters.
  • Lens: A flexible structure that focuses light onto the retina. Its shape is adjusted by ciliary muscles to allow for near and far vision.
  • Humors: The eye contains fluids called humors.
    • Aqueous humor: Fills the anterior cavity between the cornea and the lens.
    • Vitreous humor: Fills the posterior cavity between the lens and the retina, maintaining eye shape and supporting the retina.

Structural Components of the Three Layers of the Eye

  • Fibrous Layer: The outermost layer.
    • Sclera: Provides protection and shape.
    • Cornea: Focuses light.
  • Vascular Layer (Uvea): The middle layer.
    • Choroid: Contains blood vessels and pigment to absorb scattered light.
    • Ciliary Body: Controls lens shape, produces aqueous humor.
    • Iris: Controls pupil size, regulating light entry.
  • Inner Layer:
    • Retina: Contains photoreceptors (rods and cones) that transduce light into neural signals.

Pathway of Light Through the Eye and Focusing

  • Light passes through the cornea, aqueous humor, pupil, lens, and vitreous humor before reaching the retina.
  • Refraction: The bending of light rays occurs primarily at the cornea and lens.
  • The lens changes shape (accommodation) to focus light from objects at different distances.

Conversion of Light into a Neural Signal

  • Phototransduction: Light striking the retina activates photoreceptors (rods and cones).
  • Photoreceptors hyperpolarize in response to light, reducing the release of inhibitory neurotransmitters.
  • This triggers a cascade of events in bipolar cells and ganglion cells, leading to action potentials in ganglion cells.
  • Axons of ganglion cells converge to form the optic nerve, transmitting signals to the brain.

Blind Spot

  • The optic disc is the area where the optic nerve exits the eye; it contains no photoreceptors, creating a blind spot.
  • We don’t typically notice the blind spot because:
    • Each eye compensates for the other's blind spot.
    • The brain fills in the missing information.

Rods and Cones

  • Rods:
    • More sensitive to light; function in dim light.
    • Provide black and white vision.
    • Concentrated in the periphery of the retina.
  • Cones:
    • Require brighter light; function in daylight.
    • Provide color vision.
    • Concentrated in the fovea (center of the retina).

Mapping Visual Space on the Retina

  • The image is inverted and reversed on the retina due to refraction.
  • The brain corrects the image orientation during visual processing.

Structure and Function of the Ear

  • Outer Ear: Collects sound waves.
    • Pinna (auricle): Directs sound into the auditory canal.
    • Auditory Canal: Transmits sound to the tympanic membrane.
  • Middle Ear: Amplifies sound waves.
    • Tympanic Membrane (eardrum): Vibrates in response to sound.
    • Ossicles (malleus, incus, stapes): Transmit and amplify vibrations to the oval window.
  • Inner Ear: Converts sound waves into neural signals and maintains balance.
    • Cochlea: Contains receptors for hearing.
    • Vestibular Apparatus: Contains receptors for balance.

Properties of Sound

  • Loudness: Determined by the amplitude of the sound wave.
  • Pitch: Determined by the frequency of the sound wave.
  • Location: Determined by the timing and intensity differences between the two ears.

Sound Transduction

  • Sound waves cause the tympanic membrane to vibrate, which moves the ossicles.
  • The stapes transmits vibrations to the oval window, causing pressure waves in the perilymph of the cochlea.
  • These pressure waves cause the basilar membrane to vibrate.
  • Hair cells on the basilar membrane are deflected, opening mechanically gated ion channels.
  • Ion influx depolarizes the hair cells, causing them to release neurotransmitters and stimulate auditory nerve fibers.

Vestibular Apparatus

  • Semicircular Canals: Detect rotational movements.
  • Otolith Organs (utricle and saccule): Detect linear acceleration and head position.
  • Hair cells in these organs are deflected by movement, similar to those in the cochlea.

CNS Vestibular Processing Centers

  • Vestibular information is integrated in the vestibular nuclei of the brainstem.
  • Outputs project to:
    • Cerebellum: Coordination of movement.
    • Motor nuclei: Reflexive eye movements and postural adjustments.
    • Thalamus: Conscious awareness of spatial orientation and movement

Types of Deafness

  • Conductive Deafness: Impaired sound transmission through the outer or middle ear (e.g., otitis media).
  • Sensorineural Deafness: Damage to the inner ear or auditory nerve.
  • Otitis Media: Middle ear infection.
  • Tinnitus: Ringing in the ears.
  • Meniere’s Syndrome: Inner ear disorder causing vertigo, tinnitus, and hearing loss.

Chemical Senses

  • Taste (gustation): Detection of chemicals dissolved in saliva.
  • Smell (olfaction): Detection of airborne chemicals.
  • Taste and smell receptors transduce chemical signals into neural signals, which are interpreted by the brain.

Endocrine System

Endocrine vs. Exocrine Glands and the Nervous System

  • Endocrine System:
    • Releases hormones into the bloodstream.
    • Slower, longer-lasting effects.
    • Widespread effects on multiple target organs.
  • Exocrine Glands:
    • Secrete products into ducts that lead to specific locations (e.g., sweat glands, salivary glands).
  • Nervous System:
    • Uses electrical signals (action potentials) and neurotransmitters.
    • Fast, short-lived effects.
    • Localized effects.

Endocrine Disorders

  • Hyperfunction: Excessive hormone production.
  • Hypofunction: Insufficient hormone production.
  • Altered Tissue Responsiveness: Target tissues do not respond properly to hormones.
  • Primary Disorders: Problem with the gland itself.
  • Secondary Disorders: Problem with the pituitary gland.
  • Tertiary Disorders: Problem with the hypothalamus.
  • Diagnosis: Hormone level measurements, stimulation/suppression tests, imaging.

Humoral, Neural, and Hormonal Stimulation

  • Humoral Stimulation: Hormone release caused by altered levels of certain critical ions or nutrients (e.g., Ca^{2+}).
  • Neural Stimulation: Hormone release caused by neural input (e.g., adrenal medulla).
  • Hormonal Stimulation: Hormone release caused by another hormone (e.g., tropic hormones from the pituitary).

Factors Governing Hormone Levels and Negative Feedback

  • Rate of Synthesis and Release: How much hormone is being produced.
  • Rate of Degradation and Elimination: How quickly the hormone is broken down or removed from the body.
  • Negative Feedback: Rising hormone levels inhibit further hormone release.

Chemical Classes of Hormones

  • Amino Acid Derivatives:
    • Examples: epinephrine, norepinephrine, thyroid hormones.
    • Can be water-soluble or lipid-soluble.
  • Peptide Hormones:
    • Examples: insulin, growth hormone.
    • Water-soluble.
    • Bind to receptors on the cell surface.
  • Steroid Hormones:
    • Examples: cortisol, testosterone, estrogen.
    • Lipid-soluble.
    • Synthesized from cholesterol.
    • Bind to intracellular receptors.

Mechanisms of Hormone Action

  • Water-Soluble Hormones:
    • Bind to receptors on the cell membrane.
    • Activate intracellular signaling pathways (e.g., second messengers like cAMP).
    • Rapid effects.
  • Lipid-Soluble Hormones:
    • Diffuse through the cell membrane.
    • Bind to intracellular receptors in the cytoplasm or nucleus.
    • Alter gene transcription.
    • Slower, longer-lasting effects.

Pituitary Gland

  • Connected to the hypothalamus via the infundibulum.
  • Posterior Pituitary: Stores and releases hormones produced by the hypothalamus (ADH and oxytocin).
  • Anterior Pituitary: Produces and releases its own hormones, regulated by hypothalamic hormones.
  • Feedback Loops: Hormones from target glands feed back to the pituitary and hypothalamus.

Posterior Pituitary Hormones

  • Antidiuretic Hormone (ADH): Promotes water retention by the kidneys.
  • Oxytocin: Stimulates uterine contractions during childbirth and milk ejection.

Anterior Pituitary Hormones

  • Growth Hormone (GH): Promotes growth and metabolism.
  • Thyroid-Stimulating Hormone (TSH): Stimulates thyroid hormone release.
  • Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex hormone release.
  • Follicle-Stimulating Hormone (FSH): Stimulates follicle development and sperm production.
  • Luteinizing Hormone (LH): Stimulates ovulation and testosterone production.
  • Prolactin (PRL): Stimulates milk production.

Thyroid Gland

  • Located in the neck.
  • Thyroid Hormone (T3 and T4): Regulates metabolism, growth, and development.
  • Calcitonin: Lowers blood calcium levels.

Disorders Associated with Growth Hormone, Thyroid Hormone, and Adrenal Medulla Dysfunction

  • Growth Hormone:
    • Gigantism/Acromegaly: Excessive GH.
    • Dwarfism: Insufficient GH.
  • Thyroid Hormone:
    • Hyperthyroidism: Excessive TH (e.g., Graves' disease).
    • Hypothyroidism: Insufficient TH (e.g., Hashimoto's thyroiditis).
  • Adrenal Medulla Dysfunction:
    • Pheochromocytoma: Tumor of the adrenal medulla, causing excessive catecholamine release.

Adrenal Gland

  • Located on top of the kidneys.
  • Adrenal Medulla: Secretes epinephrine and norepinephrine (catecholamines).
  • Adrenal Cortex: Secretes corticosteroids (mineralocorticoids, glucocorticoids, and androgens).

Pancreas and Blood Glucose Regulation

  • Pancreas: Endocrine and exocrine functions.
  • Insulin: Decreases blood glucose levels by promoting glucose uptake by cells.
  • Glucagon: Increases blood glucose levels by stimulating glycogen breakdown in the liver.

Type I and Type II Diabetes

  • Type I Diabetes: Autoimmune destruction of pancreatic beta cells, resulting in insulin deficiency.
  • Type II Diabetes: Insulin resistance and impaired insulin secretion.

Organs in Reproductive Endocrinology

  • Ovaries (females): Produce estrogen and progesterone.
  • Testes (males): Produce testosterone.
  • Hormone Functions: Sexual development, reproductive function, and secondary sex characteristics.

Parathyroid Gland and Ca2+ Homeostasis

  • Parathyroid Gland: secretes parathyroid hormone (PTH), which increases blood Ca^{2+} levels.
  • PTH (Parathyroid Hormone):
    • Increases Ca^{2+} reabsorption in the kidneys.
    • Stimulates osteoclast activity to release Ca^{2+} from bone.
    • Increases Ca^{2+} absorption in the intestine (indirectly via vitamin D activation).
  • Disorders:
    • Hyperparathyroidism: Elevated Ca^{2+} levels.
    • Hypoparathyroidism: Low Ca^{2+} levels.

Thymus

  • Hormonal Role: secretes thymosin and thymopoietin, which promote T-cell development.
  • Immune Role: Site of T-cell maturation.

Stages of the Stress Response

  • Alarm Phase: Initial response; epinephrine release (fight or flight).
  • Resistance Phase: Long-term response; cortisol release.
  • Exhaustion Phase: Prolonged stress; depletion of resources leading to organ system failure.

Endocrine Response to Stress

  • Short-Term Stress: Increased heart rate, blood pressure, and energy mobilization.
  • Long-Term Stress: Immune suppression, increased blood glucose levels, and sodium and water retention.

Endocrine and Paracrine Signaling

  • Endocrine Signaling: Hormones travel through the bloodstream to distant target cells.
  • Paracrine Signaling: Chemicals act on nearby cells (e.g., eicosanoids).
  • Eicosanoids:
    • Locally acting signaling molecules derived from fatty acids.
    • Examples: prostaglandins, leukotrienes.