Skip to main content
Subject Knowledge 4% exam weight

Biology: Human Physiology

Part of the NAT-I (NTS) study roadmap. Subject Knowledge topic sub-6 of Subject Knowledge.

→ See in Roadmap NAT-I (NTS) Study Plans Build 1-Month Plan
By Last updated 4% exam weight

Biology: Human Physiology

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Human physiology studies how the organ systems of the human body — digestive, respiratory, circulatory, nervous, endocrine, excretory, musculoskeletal, and reproductive — function together to keep the internal environment stable, a state called homeostasis. For NAT-I (NTS), the highest-yield items are the cardiac cycle, lung volumes, blood-pressure arithmetic, the insulin/glucagon pair, and nephron function.

  • Cardiac output: CO = SV × HR (≈ 70 mL × 72 bpm ≈ 5 L/min in a resting adult)
  • Mean arterial pressure: MAP = DBP + ⅓(SBP − DBP)
  • Vital capacity: VC = TV + IRV + ERV (≈ 4600 mL in an adult male)

Remember: the right ventricle sends blood to the lungs, not the body — examiners love this reversal.

🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Organ-System Map

The body is organised as cells → tissues → organs → organ systems → organism. Each system is tested through one mechanism or number; the table below lists the must-know pairings for NAT-I (NTS).

SystemKey organ / structureDefining mechanism
DigestiveSmall intestine villiAmylase → pepsin → trypsin → lipase + bile emulsify food
RespiratoryAlveoliO₂ diffuses into blood; CO₂ out; carried by haemoglobin
CirculatoryHeart (4 chambers)Cardiac cycle: systole (contraction) + diastole (relaxation)
NervousNeuron / synapseResting potential ≈ −70 mV; action potential via Na⁺/K⁺ flux
EndocrinePancreas isletsInsulin lowers blood glucose; glucagon raises it
ExcretoryNephronFiltration → reabsorption → secretion → excretion
ReproductiveOvary / testisFSH and LH drive gametogenesis and the 28-day menstrual cycle

Core Quantitative Relationships

Three formulas recur as numerical MCQs. Memorise the variables, not just the letters.

  1. CO = SV × HR — at SV = 70 mL and HR = 72 bpm, CO ≈ 5040 mL/min ≈ 5 L/min.
  2. MAP = DBP + ⅓(SBP − DBP) — for 120/80 mmHg, MAP = 80 + ⅓(40) ≈ 93.3 mmHg.
  3. GFR = K_f × (P_GC − P_BS − π_GC) — net filtration pressure drives plasma from glomerulus to Bowman’s capsule.

Typical NAT-I Item Types

  • “Which hormone lowers blood glucose?” → Insulin (trap: glucagon raises it).
  • “Order of digestion: starch is broken down by salivary amylase in the mouth, not the stomach.”
  • MCQs on vital capacity vs tidal volume — students often confuse the two.

🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Worked Numeric — Cardiac Output and MAP

For a resting adult with SV = 70 mL/beat and HR = 72 beats/min:

  • CO = 70 × 72 = 5040 mL/min (≈ 5 L/min).
  • If BP = 120/80 mmHg, MAP = 80 + ⅓(120 − 80) = 80 + 13.33 ≈ 93.3 mmHg.

A trained endurance athlete may push CO to 25–35 L/min because stroke volume increases — heart rate alone does not scale linearly, a fact the examiner uses to test deeper understanding.

Edge Cases and Common Mistakes

MisconceptionCorrect fact
Digestion starts in the stomachSalivary amylase (ptyalin) begins starch digestion in the mouth
Tidal volume = vital capacityTidal volume ≈ 500 mL (normal breath); vital capacity ≈ 4600 mL (max exhale after max inhale)
Insulin raises blood glucoseInsulin lowers it by promoting cellular uptake and glycogen synthesis; glucagon raises it
Urine = filtrate onlyUrine is filtrate minus ~99% of water and solutes reabsorbed, plus secreted wastes
Motor vs sensory neurons swappedMotor: CNS → effector; sensory: receptor → CNS

The oxygen-haemoglobin dissociation curve (sigmoidal, shifts right with ↑CO₂, ↑H⁺, ↑temperature, ↑2,3-BPG) ties respiration to circulation. The sliding-filament theory (actin–myosin cross-bridges powered by ATP, gated by Ca²⁺ on troponin) ties musculoskeletal contraction to cellular respiration. Together they form an integrated physiology cluster that NAT-I weights as one MCQ block.

Practice Prompts

  1. A patient has BP 140/95 mmHg. Calculate MAP and identify whether this stage corresponds to Stage 1 or Stage 2 hypertension.
  2. After a carbohydrate-rich meal, trace the fate of glucose from the small intestine to its storage as hepatic glycogen, naming each hormone involved.

Continue your study

Content adapted based on your selected roadmap duration. Switch tiers using the selector above.

Sources & verification