Human Physiology & Anatomy — Part 5: 40 MCQs with Explanations

SA node in right atrial wall initiates electrical impulses at 60-100 beats per minute, setting the heart rhythm.

CO₂ from fossil fuel combustion and deforestation is the primary anthropogenic greenhouse gas, though methane and nitrous oxide also contribute significantly.

Four pulmonary veins carry oxygenated blood from lungs to left atrium. Pulmonary arteries carry deoxygenated blood from right ventricle to lungs.

Adrenaline from adrenal medulla increases heart rate, blood pressure, respiratory rate, and blood glucose levels during stress.

Calcium ions act as cofactors in several steps of the coagulation cascade, including activation of prothrombin to thrombin.

Internal respiration involves diffusion of O₂ from blood to tissues and CO₂ from tissues to blood based on partial pressure gradients.

Sutures are fibrous joints where bones are connected by dense connective tissue, allowing no movement and providing maximum protection for the brain.

Parathyroid hormone stimulates osteoclast activity to release calcium from bones, increases renal calcium reabsorption, and activates vitamin D for intestinal calcium absorption.

Fertilization typically occurs in the ampulla region of the uterine tube within 24 hours after ovulation.

Solar energy is continuously replenished by the sun on a human timescale, unlike fossil fuels which take millions of years to form.

Cerebral cortex, especially frontal and temporal lobes, handles complex cognitive processes, conscious thought, language comprehension and production.

Optic nerve (cranial nerve II) is part of the peripheral nervous system. CNS consists only of brain and spinal cord.

Oxytocin from posterior pituitary triggers uterine contractions in a positive feedback loop that intensifies until delivery.

Iris contains circular muscles (constrict pupil in bright light) and radial muscles (dilate pupil in dim light) controlled by autonomic nervous system.

Pepsinogen is activated to pepsin by HCl in stomach; pepsin hydrolyzes proteins into smaller polypeptides.

Fossil record shows: Australopithecus afarensis (e.g., 'Lucy', 3.2 mya) → Homo habilis (2.4-1.4 mya) → Homo erectus (1.9 mya-140 kya) → Homo sapiens (300 kya-present).

Progesterone prepares and maintains endometrium for implantation; if pregnancy occurs, placenta takes over progesterone production after first trimester.

Human skin is not a significant respiratory organ; gas exchange occurs primarily in lungs. Some amphibians use skin for respiration.

Adult human skeleton has 206 bones; infants have approximately 270 bones, many of which fuse during development (e.g., sacrum, coccyx).

Thyroxine increases oxygen consumption, heat production, and metabolic activity in most body tissues; deficiency causes hypothyroidism (myxedema).

Lymphatic capillaries absorb excess tissue fluid (becoming lymph), lacteals in small intestine absorb dietary fats, and lymph nodes filter pathogens.

Hypothalamus contains specialized centers for homeostatic regulation and controls pituitary gland secretion through releasing/inhibiting hormones.

Prolactin from anterior pituitary stimulates alveoli in mammary glands to produce milk; oxytocin triggers milk ejection (let-down reflex).

Homeostasis involves negative feedback mechanisms (e.g., thermoregulation, blood glucose regulation, osmoregulation) to maintain physiological constancy.

Esophagus is part of the digestive system, transporting food from pharynx to stomach; respiratory system conducts air to alveoli for gas exchange.

Adrenaline causes pupil dilation (improved vision), bronchodilation (increased airflow), increased heart rate/contractility, glycogenolysis (elevated blood glucose), and vasoconstriction in non-essential organs.

Skin does not secrete steroid hormones; endocrine glands (adrenals, gonads) produce steroids. Skin produces vitamin D₃ precursor (7-dehydrocholesterol).

Aldosterone (mineralocorticoid from adrenal cortex) acts on distal convoluted tubule and collecting duct to increase Na⁺ reabsorption and K⁺ excretion.

Medulla contains cardiac center (regulates heart rate/force), respiratory center (controls breathing rhythm), and vasomotor center (regulates blood pressure).

Spleen is part of lymphatic/immune system (filters blood, stores platelets, recycles RBCs); liver and pancreas are accessory digestive organs.

TSH secretion is regulated by thyrotropin-releasing hormone (TRH) from hypothalamus and negative feedback by circulating T3/T4 levels.

Platelets adhere to damaged endothelium, form plugs, and release clotting factors that activate coagulation cascade leading to fibrin clot formation.

Urea cycle (ornithine cycle) occurs in liver hepatocytes: 2NH₃ + CO₂ → H₂N-CO-NH₂ (urea), which is excreted by kidneys.

Colonic bacteria ferment undigested carbohydrates producing short-chain fatty acids and synthesize vitamin K and some B vitamins absorbed by host.

Albumin synthesized by liver maintains colloid osmotic pressure, preventing excessive fluid loss from capillaries into tissues.

Epididymis stores and matures sperm after production in seminiferous tubules; vas deferens transports sperm to urethra during ejaculation.

Hippocampus in medial temporal lobe consolidates short-term memories into long-term storage distributed across cerebral cortex.

LH surge triggered by high estrogen levels from mature follicle causes rupture of Graafian follicle and release of secondary oocyte (ovulation).

Atrioventricular valves (tricuspid on right, bicuspid/mitral on left) close when ventricular pressure exceeds atrial pressure, producing 'lub' heart sound.

Insulin is secreted by pancreas; kidneys regulate pH via H⁺/HCO₃⁻ excretion, produce erythropoietin (stimulates RBC production), and excrete urea/creatinine.