Human Physiology NEET Notes: Circulation and Excretion Summary

Quick answer: For NEET Human Physiology, study circulation and excretion directly from NCERT diagrams: heart chambers, valves, cardiac cycle, ECG waves, nephron structure, urine formation, counter-current mechanism and hormonal regulation. These repeated facts are high-yield for quick revision.

• Best revision method: diagram first, one-line function second, PYQ third.
• High-yield areas: cardiac cycle, ECG, nephron, ADH, RAAS and urea handling.
• NEET trap: confusing filtration, reabsorption and secretion sites in the nephron.

Circulation and Excretion give 2–3 NEET questions each year: cardiac cycle numbers, ECG waves, GFR regulation and the counter-current mechanism. These are the lines to know.

Blood

• Plasma 55% (albumin, globulin, fibrinogen); formed elements 45%.
• RBC 5–5.5 million/mm³, no nucleus, life 120 days; WBC 6000–8000 (neutrophils 60–65% most, basophils least); platelets 1.5–3.5 lakh.
• Blood groups: ABO (antigens on RBC), Rh (erythroblastosis foetalis).
• Clotting: thrombokinase → prothrombin → thrombin → fibrinogen → fibrin (Ca²⁺ needed).

Heart

• Pericardium; SA node (pacemaker, 70–75/min) → AV node → bundle of His → Purkinje fibres.
• Cardiac cycle 0.8 s: atrial systole 0.1 s, ventricular systole 0.3 s, joint diastole 0.4 s.
• Stroke volume 70 mL; cardiac output = 70 × 72 ≈ 5 L/min.
• Sounds: lub (AV valves close), dub (semilunar close).
• ECG: P (atrial depolarisation), QRS (ventricular depolarisation), T (ventricular repolarisation).
• Double circulation; portal system (hepatic); coronary circulation.

Disorders

• Hypertension > 140/90; CAD (atherosclerosis); angina; heart failure vs cardiac arrest vs heart attack.

Excretion

• Ammonotelic (fish), ureotelic (mammals), uricotelic (birds, reptiles).
• Nephron: Bowman’s capsule + glomerulus (Malpighian body), PCT, loop of Henle, DCT, collecting duct. Cortical vs juxtamedullary nephrons.
• Urine formation: glomerular filtration (GFR 125 mL/min ≈ 180 L/day), reabsorption (PCT 70–80%), secretion.
• Counter-current: loop of Henle + vasa recta; NaCl and urea keep the medulla hypertonic; concentrated urine.
• Regulation: ADH (water reabsorption), JGA → renin–angiotensin–aldosterone, ANF (reduces BP).
• Disorders: uraemia, renal calculi, glomerulonephritis; haemodialysis.

Common mistakes

• Writing ventricular systole as 0.4 s
• Saying the T wave is atrial repolarisation
• Mixing ADH (water) and aldosterone (Na⁺)

Related: Digestive system notes.

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Frequently asked questions

Is this Human Physiology NEET Notes content at JEE/NEET level?

Yes. It covers the formulas, facts and question types that appear in JEE Main, JEE Advanced and NEET, with the NCERT base that these exams follow.

How many questions come from Human Physiology NEET Notes?

Typically one to three questions per paper, depending on the year. Check the chapter-wise weightage post and give this topic time in proportion.

Where can I get human physiology NEET doubts solved quickly?

On DoubtPay AI you can type or photograph a module or mock-test question, select JEE or NEET, and get a step-by-step solution, a hint, or a check of your own attempt in seconds. ₹49 gives 100 answers with no subscription.