Anatomy and physiology essentials

In short

Anatomy is the study of the structure of the human body and physiology the study of how its parts function; together they are the foundation on which every nursing skill rests. Under the Indian Nursing Council's B.Sc Nursing curriculum (revised 2021) Anatomy and Physiology is a first-year basic-science course, usually examined in two papers or one combined paper with a practical/viva component. Clinically it decides how you position a patient, where you give an intramuscular injection, why a pulse rate of 120 with a BP of 80/50 is an emergency, and how you read an ABG or urine output chart. It is the single largest section in staff-nurse recruitment tests — AIIMS NORCET, ESIC, RRB, DSSSB, state PSC nursing exams, Military Nursing Service — and interviewers for ICU, dialysis, OT and cardiac units begin almost every technical round here.

Explained

Organisation of the body, cells, tissues and homeostasis

• Levels of organisation: chemical → cell → tissue → organ → organ system → organism. Eleven systems: integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic/immune, respiratory, digestive, urinary, reproductive.
• Anatomical position and planes: body erect, palms forward. Sagittal (left/right), coronal/frontal (front/back), transverse/axial (upper/lower). Terms: superior/inferior, medial/lateral, proximal/distal, superficial/deep, prone/supine.
• Body cavities: cranial and vertebral (dorsal); thoracic (pleural + mediastinum with pericardium) and abdominopelvic (abdominal + pelvic), separated by the diaphragm. Nine abdominal regions / four quadrants — used to localise pain (RIF pain → appendix).
• Cell organelles: nucleus (DNA), mitochondria (ATP by oxidative phosphorylation), ribosomes (protein), rough/smooth ER, Golgi (packaging), lysosomes (digestion), cell membrane (phospholipid bilayer, selectively permeable).
• Transport across membranes: passive — diffusion, osmosis, filtration, facilitated diffusion; active — Na⁺/K⁺ ATPase pump (3 Na⁺ out, 2 K⁺ in), endocytosis/phagocytosis, pinocytosis. Osmosis explains why isotonic saline (0.9% NaCl) does not lyse red cells but distilled water does.
• Four primary tissues: epithelial (covering/lining and glands — simple squamous in alveoli, pseudostratified ciliated in trachea, transitional in bladder), connective (bone, cartilage, blood, adipose, tendon), muscular (skeletal striated voluntary, cardiac striated involuntary with intercalated discs, smooth non-striated involuntary), nervous (neurons + neuroglia).
• Homeostasis: maintenance of a steady internal environment — temperature, pH, glucose, osmolarity, BP. Mostly negative feedback (rise in BP → baroreceptors → reduced sympathetic drive → BP falls). Positive feedback is rarer: oxytocin in labour, platelet plug formation.
• Membrane potential: resting potential about −70 mV (K⁺ leak + Na⁺/K⁺ pump); depolarisation by Na⁺ influx, repolarisation by K⁺ efflux, then refractory period. Basis of ECG, EEG and nerve conduction studies.

Skeletal, muscular and integumentary systems

• 206 bones in the adult (an infant has about 270; many fuse). Axial skeleton 80 (skull 22, auditory ossicles 6, hyoid 1, vertebrae 26, ribs 24, sternum 1); appendicular 126.
• Functions of bone: support, protection, movement (levers), mineral store (99% of body calcium), haematopoiesis in red marrow, fat store in yellow marrow.
• Classification by shape: long (femur, humerus), short (carpals), flat (sternum, scapula, skull), irregular (vertebra), sesamoid (patella). Parts of a long bone: diaphysis, epiphysis, epiphyseal plate (growth), periosteum, medullary cavity.
• Bone cells: osteoblasts (form), osteocytes (maintain), osteoclasts (resorb). Ossification is intramembranous or endochondral; remodelling is controlled by parathormone (raises serum Ca²⁺), calcitonin (lowers it) and calcitriol.
• Vertebral column: 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, 4 fused coccygeal = 33 bones, 26 in the adult. Lumbar puncture is done at L3–L4 or L4–L5 because the spinal cord ends at about L1–L2.
• Joints: fibrous (suture — immovable), cartilaginous (symphysis pubis — slightly movable), synovial (freely movable). Synovial types: ball-and-socket (hip, shoulder), hinge (elbow, knee), pivot (atlanto-axial), saddle (thumb), gliding (intercarpal), condyloid (wrist).
• Muscle: about 600 skeletal muscles, roughly 40% of body weight. Sliding-filament theory — nerve impulse → acetylcholine at the neuromuscular junction → depolarisation → Ca²⁺ released from sarcoplasmic reticulum → Ca²⁺ binds troponin → tropomyosin shifts → myosin heads bind actin and pull (power stroke, ATP-driven) → sarcomere shortens.
• Contraction types: isotonic (muscle shortens, joint moves) and isometric (tension without movement — quadriceps setting exercises). Muscle tone, fatigue (lactic acid, ATP depletion), oxygen debt.
• Common IM sites and their anatomy: ventrogluteal (safest in adults), vastus lateralis (infants, middle third of thigh), deltoid (2–5 cm below acromion, 0.5–2 mL only), dorsogluteal (upper outer quadrant — avoided now, sciatic nerve risk).
• Skin: epidermis (stratified squamous keratinised, avascular, with melanocytes), dermis (vessels, nerves, sweat and sebaceous glands, hair follicles), subcutaneous fat. Functions: protection, thermoregulation (sweat, vasodilatation/constriction), sensation, vitamin D synthesis, excretion. Pressure ulcers form over bony prominences — sacrum, heels, ischial tuberosities, occiput.

Cardiovascular system, blood and lymph

• Heart: four chambers, in the mediastinum, apex at the 5th left intercostal space in the midclavicular line (where the apex beat is felt). Layers: endocardium, myocardium, pericardium (fibrous + serous, with 15–50 mL pericardial fluid).
• Valves: tricuspid (RA→RV), pulmonary (RV→pulmonary artery), mitral/bicuspid (LA→LV), aortic (LV→aorta). S1 = AV valves closing, S2 = semilunar valves closing.
• Circulations: pulmonary (RV → lungs → LA, deoxygenated into the lungs) and systemic (LV → aorta → body → RA). Coronary arteries arise from the aortic root; the left coronary divides into LAD and circumflex.
• Conduction: SA node (pacemaker, 60–100/min) → AV node (40–60, delays 0.1 s) → bundle of His → right and left bundle branches → Purkinje fibres (20–40). ECG: P wave = atrial depolarisation, QRS = ventricular depolarisation, T = ventricular repolarisation; PR 0.12–0.20 s, QRS <0.12 s.
• Cardiac cycle ~0.8 s at 75 bpm: atrial systole 0.1 s, ventricular systole 0.3 s, diastole 0.4 s. Preload (end-diastolic stretch), afterload (resistance to ejection), contractility. Starling's law — the greater the diastolic filling, the stronger the contraction, within limits.
• Blood pressure = cardiac output × peripheral resistance. Regulated by baroreceptors (carotid sinus, aortic arch), chemoreceptors, the vasomotor centre in the medulla, and the renin–angiotensin–aldosterone system (renin → angiotensin I → ACE → angiotensin II: vasoconstriction + aldosterone → Na⁺ and water retention) plus ADH.
• Blood: about 5–6 L in an adult (roughly 70–80 mL/kg), 55% plasma and 45% formed elements. Plasma proteins — albumin (oncotic pressure), globulins (antibodies), fibrinogen (clotting).
• Cells: RBC 4.5–5.5 million/µL (life 120 days, destroyed in spleen/liver), WBC 4,000–11,000/µL (neutrophils 40–75%, lymphocytes 20–45%, monocytes 2–10%, eosinophils 1–6%, basophils <1%), platelets 1.5–4.5 lakh/µL (life 8–10 days).
• Haemoglobin: normal 13–17 g/dL (men), 12–15 g/dL (women). WHO/NFHS anaemia cut-offs: <13 g/dL men, <12 g/dL non-pregnant women, <11 g/dL pregnant women and children 6–59 months. Anaemia Mukt Bharat uses these.
• Haemostasis: vasoconstriction → platelet plug → coagulation cascade (intrinsic/extrinsic → common path: prothrombin → thrombin → fibrinogen → fibrin) → clot retraction → fibrinolysis. Vitamin K is needed for factors II, VII, IX, X.
• Blood groups: ABO (antigen on RBC, antibody in plasma) and Rh. O negative is the universal donor, AB positive the universal recipient. Rh-negative mother with an Rh-positive fetus → anti-D immunoglobulin to prevent haemolytic disease of the newborn. Grouping, cross-matching and the two-nurse identity check before transfusion are mandatory.
• Lymphatic system: lymph capillaries → vessels → nodes → thoracic duct (drains all but the right upper quadrant) and right lymphatic duct → subclavian veins. Organs: nodes, spleen, thymus, tonsils, Peyer's patches. Returns interstitial fluid and protein, absorbs fats as chyle, and mounts immune responses.

Respiratory system

• Parts: upper — nose, pharynx, larynx (vocal cords, epiglottis); lower — trachea (C-shaped cartilages, bifurcates at the carina, T4–T5), bronchi (the right is wider, shorter and more vertical, so aspirated material usually lodges there), bronchioles, alveoli (about 300 million, total area ~70 m²).
• Pleura: parietal and visceral with a thin film of pleural fluid; intrapleural pressure is negative (about −4 to −8 cmH₂O), which keeps the lung expanded. A breach gives pneumothorax.
• Mechanics: inspiration is active — diaphragm (main muscle, phrenic nerve C3–C5) and external intercostals contract, thoracic volume rises, intrapulmonary pressure falls, air enters. Expiration is passive, by elastic recoil. Surfactant from type II alveolar cells lowers surface tension and prevents alveolar collapse; its deficiency causes respiratory distress syndrome in preterm babies.
• Lung volumes (approximate adult values; Indian reference values are commonly 10–15% lower than classical Western figures): tidal volume 500 mL, inspiratory reserve 3,000 mL, expiratory reserve 1,100 mL, residual volume 1,200 mL, vital capacity ~4,600 mL, total lung capacity ~5,800 mL, anatomical dead space ~150 mL.
• Gas exchange: by simple diffusion across the respiratory membrane. Alveolar PO₂ ~100 mmHg vs venous blood 40 mmHg; PCO₂ 40 vs 46 mmHg. CO₂ is carried mostly as bicarbonate (~70%), some as carbamino-Hb and dissolved.
• Oxygen transport: ~97% bound to haemoglobin as oxyhaemoglobin, ~3% dissolved. The oxyhaemoglobin dissociation curve is S-shaped; it shifts right (easier unloading) with raised CO₂, H⁺, temperature and 2,3-DPG (Bohr effect), and left with alkalosis, hypothermia and fetal Hb.
• Control of breathing: respiratory centres in the medulla and pons; central chemoreceptors respond mainly to CO₂/H⁺ in CSF, peripheral ones (carotid and aortic bodies) to a large fall in PO₂. In chronic CO₂ retention the hypoxic drive dominates — the reason for cautious oxygen in COPD.
• Normal adult values: RR 12–20/min, SpO₂ 95–100%, PaO₂ 80–100 mmHg, PaCO₂ 35–45 mmHg, pH 7.35–7.45, HCO₃⁻ 22–26 mEq/L.

Digestive, urinary and fluid–electrolyte balance

• GI tract (~9 m): mouth → pharynx → oesophagus (25 cm) → stomach → duodenum, jejunum, ileum (small intestine ~6 m) → caecum, colon, rectum, anal canal. Accessory organs: salivary glands, liver, gallbladder, pancreas. Layers: mucosa, submucosa, muscularis, serosa; movements are peristalsis and segmentation.
• Secretions: saliva (amylase, 1–1.5 L/day), gastric juice (HCl from parietal cells, pepsinogen from chief cells, intrinsic factor for vitamin B12, mucus; pH 1.5–3.5), pancreatic juice (amylase, lipase, trypsinogen; alkaline), bile (bile salts emulsify fat; no enzymes), intestinal juice. Absorption is mainly in the small intestine through villi and microvilli; water and electrolytes in the colon.
• Liver functions: bile production, carbohydrate metabolism (glycogenesis, glycogenolysis, gluconeogenesis), protein and plasma-protein synthesis, deamination with urea formation, detoxification and drug metabolism, storage of iron, vitamins A, D, B12, and bilirubin conjugation.
• Urinary system: two kidneys (T12–L3, the right slightly lower), ureters, bladder, urethra (female ~4 cm, male ~20 cm — why catheter lengths and UTI risk differ). About 1 million nephrons per kidney; cortex and medulla with pyramids.
• Nephron: glomerulus in Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct. Blood supply: afferent arteriole → glomerular capillaries → efferent arteriole.
• Urine formation — three steps: (1) glomerular filtration, driven by hydrostatic pressure, GFR ~125 mL/min = about 180 L filtrate/day; (2) selective reabsorption of ~99% — glucose, amino acids, Na⁺, water, HCO₃⁻, mostly in the PCT; (3) tubular secretion of H⁺, K⁺, creatinine and some drugs. Final urine 1–2 L/day.
• Hormonal control: ADH (posterior pituitary) increases water reabsorption in collecting ducts; aldosterone retains Na⁺ and excretes K⁺; atrial natriuretic peptide promotes Na⁺ loss. Kidneys also make erythropoietin and activate vitamin D, and regulate acid–base balance.
• Body fluids: total body water ~60% of body weight in adult men, ~50–55% in women — intracellular 2/3, extracellular 1/3 (interstitial + plasma). Main intracellular cation K⁺, main extracellular cation Na⁺.
• Normal electrolytes: Na⁺ 135–145, K⁺ 3.5–5.0, Cl⁻ 98–106, HCO₃⁻ 22–26, Ca²⁺ 8.5–10.5 mg/dL, Mg²⁺ 1.5–2.5 mg/dL. Hyperkalaemia causes peaked T waves and arrhythmia; hyponatraemia causes confusion and seizures.
• Acid–base: buffers (bicarbonate, phosphate, protein, haemoglobin) act in seconds, the lungs in minutes (change CO₂), the kidneys in hours to days (excrete H⁺, retain HCO₃⁻). Four disorders — respiratory acidosis/alkalosis (primary PaCO₂ change) and metabolic acidosis/alkalosis (primary HCO₃⁻ change), each partly compensated.

Nervous system, special senses and endocrine system

• Divisions: central (brain, spinal cord) and peripheral (12 pairs of cranial nerves, 31 pairs of spinal nerves — 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal); peripheral splits into somatic and autonomic.
• Neuron: cell body, dendrites, axon, myelin sheath with nodes of Ranvier (saltatory conduction). Synaptic transmission by neurotransmitters — acetylcholine, noradrenaline, dopamine, serotonin, GABA.
• Brain: cerebrum (frontal — motor, Broca's speech, judgement; parietal — sensory; temporal — hearing, Wernicke's; occipital — vision), cerebellum (balance, coordination), brainstem — midbrain, pons, medulla (cardiac, respiratory and vasomotor centres). Hypothalamus: temperature, hunger, thirst, ADH/oxytocin, autonomic control. Meninges: dura, arachnoid, pia. CSF ~150 mL, produced ~500 mL/day by the choroid plexuses; circulates ventricles → subarachnoid space → absorbed by arachnoid villi.
• Cranial nerves I–XII: olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal. The vagus (X) carries most parasympathetic outflow; III, VII, IX, X are the cranial parasympathetic nerves.
• Reflex arc: receptor → afferent neuron → centre (spinal cord) → efferent neuron → effector. Monosynaptic (knee jerk) or polysynaptic (withdrawal).
• Autonomic nervous system: sympathetic (T1–L2, thoracolumbar, noradrenaline — "fight or flight": tachycardia, bronchodilatation, pupil dilatation, reduced gut motility) versus parasympathetic (craniosacral, acetylcholine — "rest and digest": bradycardia, increased secretion and motility, pupil constriction).
• Special senses: eye (cornea, aqueous humour, iris, lens, vitreous, retina with rods for dim light and cones for colour; image on the retina is inverted), ear (external, middle with the three ossicles and Eustachian tube, inner cochlea for hearing and semicircular canals for balance), taste, smell, and the skin receptors for touch, pressure, pain and temperature.
• Endocrine glands and chief hormones: pituitary — anterior (GH, TSH, ACTH, FSH, LH, prolactin) and posterior (ADH, oxytocin); thyroid (T3, T4 — metabolic rate; calcitonin); parathyroid (PTH); adrenal cortex (cortisol, aldosterone, androgens) and medulla (adrenaline, noradrenaline); pancreatic islets (insulin from beta cells, glucagon from alpha); gonads (oestrogen, progesterone, testosterone); pineal (melatonin); thymus (thymosin). Most are controlled by hypothalamic–pituitary negative feedback.
• Reproductive system: male — testes (spermatogenesis at ~2–3 °C below core temperature), epididymis, vas deferens, seminal vesicles, prostate, penis. Female — ovaries, fallopian tubes, uterus, cervix, vagina; the 28-day cycle has menstrual, proliferative/follicular (FSH, oestrogen), ovulatory (LH surge, ~day 14) and secretory/luteal (progesterone from the corpus luteum) phases. Fertilisation occurs in the ampulla of the fallopian tube; implantation at about day 6–7.

Key points

• Homeostasis — maintenance of a constant internal environment, mostly by negative feedback.
• 206 bones, ~600 skeletal muscles — axial 80 and appendicular 126 in the adult skeleton.
• Sliding filament theory — Ca²⁺ exposes actin binding sites and ATP-powered myosin heads shorten the sarcomere.
• Cardiac output — stroke volume × heart rate, about 5 L/min at rest; falls in shock, rises in exercise and fever.
• SA node — the pacemaker at 60–100/min; the AV node takes over at 40–60 if it fails.
• Starling's law — greater diastolic filling gives a stronger contraction, within physiological limits.
• MAP ≥ 65 mmHg — the pressure needed to perfuse brain, heart and kidneys; a key ICU target.
• Surfactant — reduces alveolar surface tension; its absence causes neonatal respiratory distress syndrome.
• Dead space (~150 mL) — airway volume that takes no part in gas exchange, so alveolar ventilation < minute ventilation.
• Bohr effect — acidosis, hypercapnia and warmth shift the O₂ dissociation curve right, releasing more O₂ to tissues.
• GFR 125 mL/min — ~180 L filtered and ~99% reabsorbed, leaving 1–2 L of urine a day.
• ADH and aldosterone — the two hormones that conserve water and sodium; central to oedema, dehydration and BP control.
• Na⁺ outside, K⁺ inside — the cardinal electrolyte rule; the Na⁺/K⁺ pump maintains it and consumes much resting ATP.
• Buffers → lungs → kidneys — acid–base defence in order of speed: seconds, minutes, hours to days.
• 31 spinal and 12 cranial nerve pairs — cord ends at L1–L2, so lumbar puncture is below it.
• Sympathetic vs parasympathetic — noradrenaline/fight-or-flight versus acetylcholine/rest-and-digest.
• Hypothalamus–pituitary axis — the master control linking nervous and endocrine systems.
• Right main bronchus — wider, shorter, more vertical, hence the usual site of aspiration.

Formulas and examples

Example 1 — Cardiac output and cardiac index. A 60 kg, 165 cm woman has HR 72/min and SV 70 mL.

• CO = 70 mL × 72 = 5,040 mL/min = 5.04 L/min.
• BSA = √(165 × 60 ÷ 3600) = √(9900 ÷ 3600) = √2.75 = 1.66 m².
• CI = 5.04 ÷ 1.66 = 3.04 L/min/m² — normal.
• If her end-diastolic volume is 120 mL, EF = 70 ÷ 120 × 100 = 58.3% — normal.

Example 2 — MAP in a hypotensive patient. BP falls from 120/80 to 80/50 mmHg.

• Before: PP = 40, MAP = 80 + 40/3 = 80 + 13.3 = 93.3 mmHg.
• After: PP = 30, MAP = 50 + 10 = 60 mmHg — below the 65 mmHg perfusion target, so report at once and expect fluids/vasopressors.

Example 3 — Ventilation and dead space. Tidal volume 500 mL, RR 14/min, dead space 150 mL.

• V̇E = 500 × 14 = 7,000 mL/min = 7 L/min.
• V̇A = (500 − 150) × 14 = 350 × 14 = 4,900 mL/min = 4.9 L/min.
• Dead-space fraction = 150 ÷ 500 = 30%. Rapid shallow breathing (TV 250, RR 28) keeps V̇E at 7 L/min but V̇A falls to (250 − 150) × 28 = 2.8 L/min — the physiological reason such a pattern retains CO₂.

Example 4 — Renal function and urine output. A 60-year-old man, 70 kg, serum creatinine 1.2 mg/dL, passed 1,200 mL of urine in 24 hours.

• Creatinine clearance = [(140 − 60) × 70] ÷ (72 × 1.2) = 5,600 ÷ 86.4 = 64.8 mL/min — about half of normal, so drug doses may need review.
• Urine output = 1,200 ÷ (70 × 24) = 1,200 ÷ 1,680 = 0.71 mL/kg/h — adequate (≥0.5), though low-normal.

Example 5 — Acid–base and osmolarity. ABG: pH 7.28, PaCO₂ 32 mmHg, HCO₃⁻ 16 mEq/L; Na⁺ 140, Cl⁻ 104, glucose 90 mg/dL, BUN 14 mg/dL.

• pH low and HCO₃⁻ low → metabolic acidosis; PaCO₂ 32 (low) shows respiratory compensation by hyperventilation.
• Anion gap = 140 − (104 + 16) = 20 mEq/L — a high-anion-gap acidosis (ketoacidosis, lactic acidosis, renal failure).
• Osmolarity ≈ (2 × 140) + (90 ÷ 18) + (14 ÷ 2.8) = 280 + 5 + 5 = 290 mOsm/kg — normal.

Example 6 — Oxygen content and drip rate. Hb 14 g/dL, SaO₂ 98%, PaO₂ 100 mmHg; 1,000 mL normal saline over 8 h with a 15 drops/mL set.

• CaO₂ = (1.34 × 14 × 0.98) + (0.003 × 100) = 18.39 + 0.30 = 18.69 mL/dL (≈187 mL/L). At Hb 7 g/dL it would be only 9.5 mL/dL — half the delivery at the same SpO₂.
• Drip rate = (1,000 × 15) ÷ (8 × 60) = 15,000 ÷ 480 = 31.25 ≈ 31 drops/min.

Where it is used

• Bedside nursing in Indian hospitals (AIIMS, PGIMER, CMC Vellore, Apollo, Fortis, Manipal, district hospitals): vital-sign interpretation, positioning (Fowler's for dyspnoea, lateral for an unconscious patient), pressure-ulcer prevention over bony prominences, and IM/IV site selection.
• Critical care, dialysis and cardiac units: haemodynamic monitoring (MAP, CVP), ventilator settings and ABG reading, fluid and electrolyte correction, ECG rhythm recognition — the skills tested in ICU and CCU nurse interviews.
• Operating theatre and anaesthesia assistance: surface anatomy and landmarks for spinal/epidural levels, airway anatomy for intubation assistance, positioning to avoid nerve injury.
• Community health and national programmes: anaemia screening under Anaemia Mukt Bharat, BP and diabetes screening under NP-NCD, antenatal care and growth monitoring — all applied physiology.
• Entrance and recruitment examinations: NORCET, ESIC, RRB, DSSSB, state PSC staff nurse, Military Nursing Service, and M.Sc Nursing entrances devote a large block to anatomy and physiology.
• Allied roles: nurse educators and clinical instructors in INC-recognised colleges, medical-device and pharma clinical-support roles, medical coding and health-insurance claim review, and medical transcription — all needing structural and functional vocabulary.

Interview questions

• Q: Define homeostasis and give one clinical example. A: The maintenance of a stable internal environment within narrow limits. Example: a rise in blood pressure stimulates baroreceptors, which reduce sympathetic outflow so that pressure falls back — negative feedback.
• Q: Trace the path of blood from the right atrium back to it. A: Right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary artery → lungs (oxygenation) → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → systemic circulation → venae cavae → right atrium.
• Q: What is cardiac output and what is normal? A: The volume of blood ejected by each ventricle per minute — stroke volume × heart rate, about 4–6 L/min at rest in an adult.
• Q: Why is MAP more important than systolic pressure in a critically ill patient? A: MAP is the average pressure driving blood through tissues over the whole cardiac cycle, so it reflects organ perfusion; a MAP below about 65 mmHg risks renal and cerebral ischaemia even if the systolic looks acceptable.
• Q: Name the parts of the conduction system of the heart in order. A: SA node, AV node, bundle of His, right and left bundle branches, Purkinje fibres.
• Q: What is surfactant and why does it matter in a preterm baby? A: A phospholipid secreted by type II alveolar cells that lowers alveolar surface tension and prevents collapse; preterm lungs have too little, causing respiratory distress syndrome.
• Q: Why does a foreign body usually enter the right lung? A: The right main bronchus is wider, shorter and more vertical than the left.
• Q: List the three steps of urine formation. A: Glomerular filtration in Bowman's capsule, selective reabsorption mainly in the proximal tubule and loop of Henle, and tubular secretion of H⁺, K⁺ and some drugs into the tubule.
• Q: A patient's ABG shows pH 7.30, PaCO₂ 55 mmHg, HCO₃⁻ 26. Interpretation? A: Uncompensated respiratory acidosis — the low pH is driven by the raised PaCO₂ while bicarbonate is still normal, as in hypoventilation or an acute COPD exacerbation.
• Q: Which hormones control water and sodium balance? A: ADH from the posterior pituitary increases water reabsorption in the collecting ducts; aldosterone from the adrenal cortex retains sodium and excretes potassium; atrial natriuretic peptide opposes both.
• Q: At which level is a lumbar puncture performed and why? A: At L3–L4 or L4–L5, because the spinal cord terminates at about L1–L2, so only the cauda equina nerve roots are present and they move aside from the needle.
• Q: Why is O negative called the universal donor? A: O red cells carry neither A nor B antigen and, being Rh negative, no D antigen, so recipient anti-A, anti-B or anti-D antibodies have nothing to agglutinate — though in practice group-specific cross-matched blood is always preferred.
• Q: What does a right shift of the oxygen dissociation curve mean for the patient? A: Haemoglobin's affinity for oxygen is reduced, so more oxygen is unloaded in tissues — seen in fever, acidosis and hypercapnia.

Common mistakes

• Confusing cardiac output with stroke volume, or quoting stroke volume in litres while heart rate is per minute without converting units.
• Calculating MAP as the simple average of systolic and diastolic instead of DBP + PP/3 — diastole lasts longer than systole.
• Mixing up the sympathetic and parasympathetic effects, especially on the pupil and bronchi, in viva.
• Writing that minute ventilation equals alveolar ventilation — dead space (~150 mL) must be subtracted from each breath.
• Reversing ABO antigens and antibodies (group A has A antigen and anti-B antibody), which is a dangerous error in transfusion practice.
• Applying international BMI cut-offs to Indian patients; ICMR/Asian-Indian thresholds are lower — overweight from 23 and obese from 25.
• Describing inspiration as passive and expiration as active; at rest it is the opposite.
• Giving classical Western lung volumes as exact Indian norms, and forgetting that values vary with age, sex, height and ethnicity.

Related topics

Microbiology for nurses · Pharmacology for nurses · Nutrition and dietetics · Medical-surgical nursing · Fundamentals of nursing and vital signs · Biochemistry and laboratory values