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Anatomy & Physiology: Special Senses, Endocrine, Blood, Cardiovascular, Lymphatic, Respiratory, Digestive, Metabolism, Urinary, Fluid Balance, Reproductive, and Development

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Special Senses

Vision

The human eye is a complex organ responsible for detecting light and transmitting visual information to the brain. Its wall consists of three main layers, each with distinct functions.

  • Fibrous Layer: The outermost layer, composed of the sclera (white of the eye) and the cornea (transparent anterior portion).

  • Vascular Layer: The middle layer, including the choroid (provides blood supply), ciliary body (controls lens shape), and iris (regulates pupil size).

  • Retina: The innermost layer, containing photoreceptors:

    • Rods: Specialized for dim-light and peripheral vision.

    • Cones: Responsible for high-resolution color vision.

Hearing & Equilibrium

The ear is divided into external, middle, and internal regions, each contributing to hearing and balance.

  • Middle Ear: Contains the auditory ossicles (malleus, incus, stapes) that transmit sound vibrations to the internal ear.

  • Internal Ear (Labyrinth): Houses the cochlea (hearing) and the vestibule and semicircular canals (equilibrium and balance).

Endocrine System

Hormone Mechanism

The endocrine system regulates body activities by releasing hormones directly into the bloodstream. Hormones affect only target cells with specific receptors.

  • Hormones: Chemical messengers that coordinate physiological processes.

  • Target Cells: Cells with receptors for a specific hormone.

Major Endocrine Glands

  • Pituitary Gland:

    • Posterior Lobe: Stores and releases ADH (antidiuretic hormone, water balance) and oxytocin (uterine contractions, milk ejection).

    • Anterior Lobe: Produces hormones such as GH (growth hormone), TSH (thyroid-stimulating hormone), and ACTH (adrenocorticotropic hormone).

  • Thyroid/Parathyroid Glands:

    • Thyroid Hormone (TH): Regulates basal metabolic rate.

    • Parathyroid Hormone (PTH): Essential for calcium homeostasis.

  • Pancreas: Regulates blood glucose via insulin (lowers glucose) and glucagon (raises glucose).

Blood

Composition

Blood is a connective tissue consisting of plasma and formed elements.

  • Plasma: Nonliving fluid matrix (~55% of blood volume), contains proteins (e.g., albumin for osmotic pressure).

  • Formed Elements: Cellular components:

    • Erythrocytes (RBCs): Anucleate discs filled with hemoglobin for gas transport.

    • Leukocytes (WBCs): Immune defense; types include neutrophils (phagocytosis), B lymphocytes (antibody production), and monocytes (differentiate into macrophages).

    • Platelets: Cell fragments involved in clotting.

Hemostasis

Hemostasis is the process of stopping bleeding, involving three steps:

  1. Vascular Spasm

  2. Platelet Plug Formation

  3. Coagulation

Cardiovascular System: The Heart

Circuits

The heart pumps blood through two main circuits:

  • Pulmonary Circuit: Right side pumps oxygen-poor blood to the lungs.

  • Systemic Circuit: Left side pumps oxygen-rich blood to the body.

Valves

  • Atrioventricular (AV) Valves: Tricuspid (right) and mitral (left); prevent backflow into atria during ventricular contraction.

  • Semilunar Valves: Prevent backflow into ventricles.

Conduction System

  • Sinoatrial (SA) Node: The heart's intrinsic pacemaker, initiates each heartbeat (sinus rhythm).

Cardiovascular System: Blood Vessels

Vessel Types

  • Arteries: Carry blood away from the heart.

  • Veins: Carry blood toward the heart.

  • Capillaries: Sites of gas and nutrient exchange.

Resistance and Pressure

  • Peripheral Resistance: Most influenced by vessel diameter.

  • Systemic Pressure: Highest in the aorta; steepest drop in arterioles.

Lymphatic and Immune Systems

Lymphatic System

  • Lymph: Fluid returned to the blood from tissues.

  • Lymph Nodes: Filter lymph for pathogens.

  • Spleen: Largest lymphoid organ; cleanses blood of aged cells and debris.

Immunity

  • Innate Immunity: Nonspecific, includes barriers (skin) and inflammation.

  • Adaptive Immunity: Specific, systemic, and has memory.

  • T Cell Roles:

    • Helper T Cells (TH): Activate B and T cells.

    • Cytotoxic T Cells (TC): Destroy infected or cancerous cells.

Respiratory System

Processes of Respiration

  • Pulmonary Ventilation: Breathing; movement of air into and out of lungs.

  • External Respiration: Gas exchange between lungs and blood.

Gas Exchange and Laws

  • Respiratory Membrane: Site of gas exchange via simple diffusion.

  • Boyle’s Law: As thoracic volume increases, gas pressure decreases, causing air to flow in.

Lung Volumes

  • Tidal Volume (TV): Amount of air moved during a normal breath (~500 mL).

Digestive System

Stomach

  • Parietal Cells: Secrete HCl (acidifies stomach) and intrinsic factor (essential for Vitamin B12 absorption).

Small Intestine

  • Major Site: Digestion and absorption of nutrients.

  • Surface Area: Increased 600x by circular folds, villi, and microvilli.

Gut Brain

  • Enteric Nervous System: Manages digestion independently; contains more neurons than the spinal cord.

Nutrition and Metabolism

Fuel and Fiber

  • Glucose: Primary monosaccharide used for ATP production.

  • Insoluble Fiber (Cellulose): Provides roughage for defecation.

  • Soluble Fiber (Pectin): Helps lower blood cholesterol.

Metabolic Rate

  • Basal Metabolic Rate (BMR): Primarily controlled by thyroxine.

Urinary System

Nephron Structure

  • Nephron: Functional unit of the kidney; consists of a renal corpuscle (glomerulus and capsule) and a renal tubule.

Urine Formation

  • Glomerular Filtration

  • Tubular Reabsorption: Returns 99% of filtrate to blood.

  • Tubular Secretion

Regulation

  • ADH: Increases water reabsorption in collecting ducts.

  • Aldosterone: Promotes sodium reabsorption; water follows sodium.

Fluid, Electrolyte, and Acid-Base Balance

Fluid Compartments

  • Intracellular Fluid (ICF): Fluid within cells.

  • Extracellular Fluid (ECF): Fluid outside cells.

  • Sodium (Na+): Major cation of ECF.

  • Potassium (K+): Major cation of ICF.

Acid-Base Balance

  • Blood pH: Maintained between 7.35 and 7.45.

  • Buffers: Chemical (e.g., bicarbonate), respiratory, and renal systems resist pH changes.

Reproductive System

Male Reproductive System

  • Testes: Produce sperm and testosterone.

  • Semen: Contains secretions that enhance sperm motility and neutralize acidic urine.

Female Reproductive System

  • Uterine (Fallopian) Tubes: Usual site of fertilization.

  • Uterus: Three layers: perimetrium (outer), myometrium (muscular), endometrium (shed during menstruation).

Ovarian Cycle

  • Ovulation: Release of mature oocyte (mid-cycle).

  • Luteal Phase: Corpus luteum secretes progesterone.

Pregnancy and Human Development

Fertilization and Early Development

  • Fertilization: Sperm and oocyte chromosomes combine to form a zygote.

  • Placenta: Temporary organ for nutrition, respiration, and hormone secretion (e.g., hCG).

  • Gastrulation: Formation of three germ layers (ectoderm, mesoderm, endoderm) during week 3.

Labor

  • Initiation: Triggered by estrogen and oxytocin surge.

  • Stages: Dilation, expulsion of infant, placental stage.

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