Human Physiology & Anatomy — Part 6: 38 MCQs with Explanations

Large intestine absorbs remaining water and electrolytes from indigestible food matter, forming solid feces; most nutrient absorption occurs in small intestine.

Skin contains 7-dehydrocholesterol converted to vitamin D₃ precursor upon UV exposure; liver and kidneys complete activation to calcitriol.

Estrogen from ovarian follicles promotes breast development, widening of hips, and distribution of subcutaneous fat characteristic of females.

Melatonin secreted by pineal gland increases at night promoting sleepiness; light exposure suppresses its production.

External respiration involves diffusion of O₂ from alveoli into blood and CO₂ from blood into alveoli based on partial pressure gradients.

AB positive is universal recipient for RBC transfusion because plasma lacks anti-A and anti-B antibodies; however, cross-matching is still preferred.

Adrenocorticotropic hormone (ACTH) from anterior pituitary stimulates adrenal cortex to produce glucocorticoids (cortisol), mineralocorticoids (aldosterone), and androgens.

Medulla oblongata contains cardiac center regulating heart rate/force, respiratory center controlling breathing rhythm, and vasomotor center regulating blood pressure.

Estrogen promotes development of breasts, widening of pelvis, and characteristic fat distribution in females during puberty.

Esophagus is part of digestive system transporting food to stomach; respiratory system includes nasal cavity, pharynx, larynx, trachea, bronchi, and lungs.

Calcium ions bind to troponin, causing conformational change that moves tropomyosin away from myosin-binding sites on actin filaments.

External respiration involves diffusion of O₂ from alveoli into pulmonary capillaries and CO₂ from capillaries into alveoli.

Hormone production is endocrine system function; bones store calcium and phosphate, provide attachment for muscles, and protect vital organs.

Vitamin D deficiency impairs calcium absorption, causing soft, weak bones; in children this manifests as rickets (bowing of legs, enlarged joints).

Synovial joints (e.g., knee, shoulder) have articular cartilage, synovial fluid, and joint capsule allowing free movement.

Implantation occurs 6-7 days after fertilization when blastocyst attaches to and embeds in endometrium of uterine wall.

Coal is a fossil fuel formed over millions of years; consumption rate far exceeds formation rate, making it non-renewable on human timescale.

Optic nerve (cranial nerve II) transmits visual information from retina to visual cortex; it is technically a brain tract rather than true peripheral nerve.

Oxytocin triggers powerful rhythmic contractions of myometrium; positive feedback loop intensifies contractions until delivery.

Thiamine deficiency impairs carbohydrate metabolism and nerve function, causing dry beriberi (neurological) or wet beriberi (cardiovascular).

Pancreatic lipase hydrolyzes triglycerides into fatty acids and monoglycerides; bile salts emulsify fats to increase enzyme access.

Australopithecus (e.g., A. afarensis 'Lucy') lived 4-2 million years ago and shows mosaic of ape-like and human-like features including bipedalism.

Skin does not secrete hormones into bloodstream; endocrine glands (pituitary, thyroid, adrenals, etc.) perform hormone secretion.

Axial skeleton (skull, vertebral column, rib cage) has 80 bones; appendicular skeleton (limbs, girdles) has 126 bones; total 206.

CSF is produced by choroid plexuses in brain ventricles, circulates in subarachnoid space, and is reabsorbed into venous blood.

Thyroxine (T4) increases basal metabolic rate, oxygen consumption, and thermogenesis; deficiency causes hypothyroidism with reduced metabolism.

Glomerulus is a tuft of capillaries where high hydrostatic pressure forces water and small solutes out of blood into Bowman's capsule.

Thoracic duct drains lymph from entire body below diaphragm and left upper body into left subclavian vein; right lymphatic duct drains right upper body.

Hypothalamus produces releasing/inhibiting hormones that regulate anterior pituitary secretion and synthesizes oxytocin/ADH stored in posterior pituitary.

Gallbladder stores and concentrates bile produced by liver; liver synthesizes bile salts from cholesterol.

Progesterone from corpus luteum (later placenta) maintains thickened endometrium, suppresses uterine contractions, and prevents further ovulation.

Small intestine (especially jejunum) has villi and microvilli increasing surface area ~600-fold for efficient absorption of monosaccharides, amino acids, fatty acids, vitamins, and minerals.

Homeostasis involves negative feedback loops (e.g., thermoregulation, blood glucose control) to maintain physiological parameters within narrow ranges.

Sympathetic division ('fight or flight') inhibits digestion; parasympathetic division ('rest and digest') stimulates digestive secretions and motility.

Parasitism: parasite (tapeworm) benefits at expense of host (human) who is harmed by nutrient deprivation and tissue damage.

Aldosterone acts on distal convoluted tubule and collecting duct to increase Na⁺ reabsorption (and thus water retention) and K⁺ secretion.

Adrenocorticotropic hormone (ACTH) from anterior pituitary stimulates adrenal cortex zona fasciculata to produce glucocorticoids (mainly cortisol).

PTH stimulates osteoclasts to break down bone matrix releasing calcium; also increases renal calcium reabsorption and activates vitamin D for intestinal absorption.