Human Physiology & Anatomy — Part 4: 40 MCQs with Explanations

Adrenaline (epinephrine) and noradrenaline are secreted by adrenal medulla during sympathetic activation ('fight or flight').

Arteries (especially elastic arteries) have thick tunica media with smooth muscle and elastic fibers to withstand high pressure and regulate flow.

Fish gills have countercurrent flow system where water and blood flow in opposite directions, maximizing O₂ diffusion efficiency.

PTH increases blood Ca²⁺ by stimulating bone resorption, renal reabsorption, and vitamin D activation.

7-Dehydrocholesterol in skin is converted to cholecalciferol (vitamin D₃) upon UV-B exposure, later activated in liver/kidneys.

SA node initiates heartbeat at 60-100 bpm; AV node (40-60 bpm) and Purkinje fibers (20-40 bpm) act as backup pacemakers.

Thrombocytes (platelets) form plugs at injury sites and release clotting factors for coagulation cascade.

The lens fine-tunes focus (accommodation) by changing shape via ciliary muscles; cornea provides most refraction.

Urea is less toxic than ammonia and requires moderate water for excretion; uric acid is excreted by birds/reptiles; ammonia by aquatic animals.

Oxytocin and ADH are synthesized in hypothalamus and stored/released from posterior pituitary (neural tissue).

Arteries carry blood away from the heart (usually oxygenated except for pulmonary artery). Veins carry blood toward the heart.

The nephron consists of renal corpuscle (glomerulus + Bowman's capsule) and renal tubule, performing filtration, reabsorption, and secretion.

Thyroxine (T4) and triiodothyronine (T3) increase basal metabolic rate, affect protein synthesis, and regulate development and growth.

Fertilization usually occurs in the ampulla region of the fallopian tube (oviduct), after which the zygote moves to the uterus for implantation.

Vitamin K is synthesized by Escherichia coli and other bacteria in the colon and is essential for blood clotting factor synthesis.

The appendix is considered vestigial—a remnant of a larger cecum that was functional in herbivorous ancestors for cellulose digestion.

The sarcomere, defined as the segment between two Z-lines, is the basic contractile unit of striated muscle containing actin and myosin filaments.

Parathormone (PTH), secreted by parathyroid glands, increases blood calcium levels by stimulating bone resorption, kidney reabsorption, and vitamin D activation.

Amylase (salivary and pancreatic) hydrolyzes starch into maltose and other small carbohydrates.

Sinoatrial (SA) node in right atrium initiates electrical impulses (60-100 bpm), setting heart rhythm.

Calcium ions (Ca²⁺) are required for several steps in coagulation cascade, including conversion of prothrombin to thrombin.

Internal respiration involves O₂ diffusion from blood to tissues and CO₂ diffusion from tissues to blood.

Skull bones are connected by immovable fibrous joints (sutures) providing protection to the brain.

Cerebral cortex (especially frontal lobe) handles reasoning, problem-solving, language, and conscious thought.

Cranial nerves are part of peripheral nervous system (PNS). CNS consists of brain and spinal cord only.

Erythrocytes (RBCs) contain hemoglobin which binds and transports O₂ from lungs to tissues.

Pepsin (activated from pepsinogen by HCl) breaks proteins into smaller peptides in acidic gastric environment.

Corpus luteum secretes progesterone (and some estrogen) to maintain endometrium for potential implantation during menstrual cycle.

Gas exchange occurs primarily in lungs (humans); skin is not a significant respiratory organ except in some amphibians.

Adult human skeleton has 206 bones (infants have ~270, many fuse during development).

Thyroxine (T4) from thyroid gland increases oxygen consumption and heat production, elevating basal metabolic rate.

Prolactin from anterior pituitary stimulates mammary glands to produce milk (lactogenesis).

Adrenaline (epinephrine) dilates airways (bronchioles), increases heart rate and force, dilates pupils, and elevates blood glucose during stress response.

Aldosterone (mineralocorticoid from adrenal cortex) increases Na⁺ reabsorption and K⁺ excretion in distal convoluted tubule and collecting duct.

Medulla oblongata contains cardiac, respiratory, and vasomotor centers regulating involuntary vital functions.

Antidiuretic hormone (ADH/vasopressin) increases permeability of collecting ducts to water, promoting water reabsorption and concentrated urine.

Nephron consists of glomerulus, Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

Appendix has lost most of its ancestral digestive function in herbivores; in humans it may have minor immune functions but is largely vestigial.

Escherichia coli and other gut bacteria synthesize vitamin K, essential for synthesis of blood clotting factors II, VII, IX, and X.

Cerebellum receives input from vestibular system, proprioceptors, and motor cortex to coordinate voluntary movements and maintain equilibrium.