HESI A2 A&P cheat sheet

Anatomical position: body erect, face forward, arms at sides with palms anterior; directional terms (superior/inferior, anterior/posterior, medial/lateral, proximal/distal, superficial/deep) are defined only from this stance.

Body cavities: dorsal cavity = cranial + vertebral (spinal); ventral cavity = thoracic (pleural, pericardial, mediastinum) + abdominothoracic diaphragm separation from abdominopelvic (abdominal, pelvic). The diaphragm separates thoracic from abdominal cavities.

Four tissue classes: epithelial (covering/lining, avascular, apical surface, basement membrane), connective (cells in extracellular matrix; bone, cartilage, blood, adipose), muscle (skeletal striated voluntary, cardiac striated involuntary intercalated discs, smooth nonstriated involuntary), nervous (neurons + neuroglia).

Homeostasis: negative feedback reverses a deviation (thermoregulation, blood glucose via insulin/glucagon, blood pressure baroreflex); positive feedback amplifies (oxytocin in labor, thrombin in clotting). Receptor → control center → effector is the standard loop.

Cell transport: diffusion and osmosis are passive (high to low concentration, no ATP); facilitated diffusion uses channels/carriers without ATP; primary active transport uses ATP (Na+/K+ pump moves 3 Na+ out and 2 K+ in); endocytosis/exocytosis are vesicular bulk transport.

Osmolarity rules: isotonic = no net water shift; hypertonic solution causes cell shrinkage (crenation); hypotonic causes cell swelling and possible lysis. Osmosis moves water toward the higher solute concentration.

Organelle functions: nucleus holds DNA; ribosomes synthesize protein; rough ER folds/transports protein; smooth ER makes lipids and detoxifies; Golgi modifies and packages; mitochondria produce ATP via aerobic respiration; lysosomes digest; cytoskeleton maintains shape and moves materials.

Cell cycle: interphase (G1, S = DNA replication, G2) precedes mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis; mitosis produces two genetically identical diploid cells, whereas meiosis produces four haploid gametes.

Membrane potential and signaling: resting potential is about -70 mV maintained by the Na+/K+ pump and K+ leak; depolarization makes the inside less negative, repolarization restores it; neurons conduct via action potentials and communicate across synapses by neurotransmitter release.

Skeletal system: 206 bones in the adult; axial skeleton (skull, vertebral column, rib cage, hyoid) supports and protects, appendicular skeleton (limbs and girdles) enables movement. Osteoblasts build bone, osteoclasts resorb bone, osteocytes maintain matrix.

Muscle contraction: sliding filament theory - Ca2+ binds troponin, tropomyosin shifts, myosin heads bind actin and pull thin filaments toward the sarcomere center; ATP is required for both the power stroke and detachment. Acetylcholine released at the neuromuscular junction triggers depolarization.

Cardiac cycle and conduction: SA node (pacemaker) → AV node → bundle of His → bundle branches → Purkinje fibers. Systole = contraction/ejection; diastole = relaxation/filling. Cardiac output = heart rate × stroke volume.

Blood vessel and pressure rules: arteries carry blood away from the heart (thick tunica media), veins carry toward the heart and contain valves, capillaries are one cell thick for exchange. Blood pressure = cardiac output × peripheral resistance.

Blood composition: plasma ~55% (mostly water, plus albumin, globulins, fibrinogen); formed elements ~45% (hematocrit). Erythrocytes carry O2 on hemoglobin and lack a nucleus; leukocytes defend; platelets (thrombocytes) mediate hemostasis.

Blood typing: ABO and Rh antigens on RBCs; type O negative is the universal donor for red cells, AB positive is the universal recipient. Rh-negative mother with Rh-positive fetus risks hemolytic disease of the newborn.

Respiratory mechanics: inspiration is active - diaphragm contracts and flattens, external intercostals lift ribs, thoracic volume rises and intrapulmonary pressure falls below atmospheric. Expiration is usually passive recoil. Gas exchange occurs at alveolar-capillary membranes by diffusion; surfactant reduces surface tension.

Digestive and urinary essentials: most nutrient absorption occurs in the small intestine (villi and microvilli increase surface area); the large intestine absorbs water and electrolytes. The nephron filters at the glomerulus, reabsorbs mostly in the proximal tubule, and secretes/regulates via the loop of Henle and collecting duct under ADH and aldosterone.

Endocrine and nervous integration: the hypothalamus controls the anterior pituitary; tropic hormones (TSH, ACTH, FSH, LH) regulate other glands. Insulin lowers blood glucose, glucagon raises it. The autonomic nervous system uses sympathetic (fight-or-flight, norepinephrine) and parasympathetic (rest-and-digest, acetylcholine via vagus) divisions.