Human Anatomy & Physiology Lecture Vocabulary Review

Homeostasis & Feedback Mechanisms

• Homeostasis: maintenance of a relatively constant internal environment within an organism; ensures optimal conditions for cellular functions.
  • Example: Thermoregulation—when body temperature rises, the hypothalamic center initiates physiological changes (e.g., sweating, vasodilation) to decrease temperature.
• Negative feedback: primary regulatory mechanism; output of a system counteracts a deviation (e.g., heat loss reduces body temperature back toward set-point).
  • Significance: prevents sudden, severe changes; stabilizes physiological variables.

Body Cavities & Major Anatomical Landmarks

• Thoracic cavity is separated from the abdominopelvic cavity by the diaphragm muscle.
  • Thoracic cavity subdivisions:
  • Pleural cavities (surround lungs)
  • Pericardial cavity (surrounds heart) located within the mediastinum.
• Mediastinum: central mass of tissue separating right & left pleural cavities; contains pericardium, esophagus, trachea, major vessels.
• Liver: primarily in the right upper quadrant (clinical significance for abdominal assessment).

Chemical Foundations

• Ionization of salts in water ➔ production of ions capable of carrying electric current; such ion-rich solutions are electrolytes.
• Body pH: closest to neutral, approximately 7.
• Buffers: prevent drastic pH shifts; major physiological buffer is \text{NaHCO}_3 (sodium bicarbonate).
• Metabolic fuel: Glucose is the most important; enters glycolysis, citric acid cycle, oxidative phosphorylation.
• Lipids:
  • Structural components of membranes (e.g., phospholipids, cholesterol).
  • Dense energy reserves ( ≈ 9\,\text{kcal g}^{-1} compared with carbs/proteins).
  • Cushion & insulate organs against mechanical shocks.
• Enzyme cofactors: non-protein helpers (metal ions, vitamins) required for catalytic activity; absence makes enzyme non-functional.

Cellular Components & Physiology

• Cytosolic enzymes accelerate metabolic reactions (e.g., glycolytic enzymes).
• Plasma-membrane proteins function as:
  • Receptors (signal transduction)
  • Enzymes (local catalysis)
  • Recognition (identity) proteins (e.g., MHC)
  • Anchoring proteins (attachment to cytoskeleton/ECM)
• Cytosol vs. ECF: higher \text{K}^+ concentration inside; lower \text{Na}^+.
• Mature erythrocytes: anucleate; cannot synthesize new proteins ➔ limited lifespan (≈ 120 days), removed by spleen/liver.
• Pulmonary ventilation: deeper/faster breathing decreases arterial \text{CO}_2 ➔ enhanced diffusion gradient in lungs, assists acid–base balance.

Cell Cycle & Division

• Mitosis produces two genetically identical daughter cells (same chromosome number as parent, 2n).

Histology

• Epithelia: avascular sheets lining cavities; example—multiple layers without vessels on cavity surface indicates stratified epithelium.
• Simple squamous epithelium lines heart, blood vessels (endothelium), alveoli; thin for rapid diffusion.
• Gland types:
  • Endocrine: ductless, secrete hormones into interstitial fluid/blood.
  • Exocrine: ducts to surface (pancreas uniquely both endocrine & exocrine).
• Connective-tissue matrix: ground substance + fibers (collagen, elastic, reticular).

Integumentary System

• Functions: protection, thermoregulation, lipid storage, vitamin D₃ synthesis, sensory detection—NOT vitamin C synthesis.
• Keratin: fibrous protein produced by keratinocytes; waterproofs & toughens epidermis.
• Cyanosis: bluish skin due to oxygen-starved hemoglobin; clinical sign of hypoxemia.
• Cleavage (Langer’s) lines: collagen fiber orientation in dermis; incisions parallel heal with minimal scarring.
• Thermoregulation: when core temperature rises above normal, cutaneous blood flow increases for heat dissipation.
• Burn classification: ability to pull out whole hair follicles indicates destruction through dermis—third-degree burn (full-thickness).

Skeletal Tissue & Physiology

• Osteoblasts: synthesize organic bone matrix (osteoid—collagen + ground substance); initiate deposition.
• Osteons: primary structural units of compact bone (mis-labeled “osteosarcoma” in transcript; actual term = osteon).
• Epiphyseal line in a 10-year-old implies plates have fused; longitudinal growth ceased (premature closure).
• Vitamin D₃: promotes intestinal calcium absorption; essential for calcification & remodeling (
  indirect link to calcitonin mis-stated in transcript).
• Post-menopausal osteoporosis (e.g., 50-year-old Mary): recommend adequate \text{Ca}^{2+}, vitamin D, weight-bearing exercise; possibly bisphosphonates/estrogen therapy.

Axial & Appendicular Skeleton Highlights

• Hypophyseal fossa (sella turcica) of sphenoid houses pituitary gland (endocrine significance).
• Temporal bone damage ➔ potential hearing & balance deficits (contains auditory apparatus).
• Mandibular condylar process: forms temporomandibular joint; dislocation causes jaw displacement.
• Paranasal sinuses: lighten skull, resonate voice, humidify & warm air.
• Vertebral body: bears/ transfers axial load.
• CPR hand placement: inferior sternum risks fracturing ribs/xiphoid; correct placement on lower half of sternum mitigates.
• Pisiform fracture: involves carpal bone on ulnar side of wrist (fall injury common).
• Weight distribution in standing: mainly through calcaneus & talus (posterior & anterior aspects of plantar arch).

Articulations

• Synovial joint = diarthrosis (freely movable).
• Greatest mobility: glenohumeral (shoulder) joint (triaxial ball-and-socket).
• Cruciate ligaments (ACL & PCL) in knee: constrain anterior–posterior tibial movement, maintain femoro-tibial alignment; frequently injured in athletics.

Skeletal-Muscle Organization & Contraction

• Structural hierarchy (superficial ➔ deep):
  • Epimysium ➔ Perimysium ➔ Fascicle ➔ Endomysium ➔ Muscle fiber ➔ Myofibril.
• Excitation–contraction coupling:
  • Action potentials travel along sarcolemma & T-tubules.
  • Sarcoplasmic reticulum (SR) releases \text{Ca}^{2+} into cytosol.
  • \text{Ca}^{2+} binds troponin, exposes actin active sites ➔ cross-bridge cycling.
• Neuromuscular junction:
  • Synaptic vesicles store acetylcholine (ACh).
  • ACh binds motor-end-plate receptors ➔ depolarization.
• High ATP demand ➔ abundant mitochondria & capillary supply; reliance on oxidative phosphorylation during sustained activity.
• Sarcomere: repeating unit between Z-lines; contains A-band (thick filaments) & I-band (thin); fundamental contractile unit.
• Elevated thyroid hormone would:
  • Increase basal metabolic rate of muscle fibers.
  • Enhance ATP turnover & heat production; may potentiate reflex activity & protein catabolism if chronic.

Clinical & Functional Connections

• Disruption of homeostasis underlies many pathologies (burns, osteoporosis, acidosis/alkalosis).
• Joint anatomy informs injury mechanisms (e.g., ACL tears during valgus stress).
• Cellular/tissue knowledge guides interventions (e.g., dermal cleavage lines for surgery, buffer therapy for acidosis).
• Aging & endocrine changes (menopause, thyroid excess) significantly affect bone & muscle physiology.