Schooling · Class 11 · Biology · Body Fluids and Circulation · Chapter on a page
CBSE Class 11 · Biology · NCERT Biology
Body Fluids and Circulation: chapter on a page
A cut of Shishya's notes for this chapter: the first paragraph of the introduction and the key ideas, formulas and facts, common mistakes and quick revision lists, word for word. Nothing is added or reworded; the worked examples are left out (they are on the chapter page).
About the notes: Written by Shishya's AI on 27 Sept 2026 from the chapter's title and class level, in Shishya's own words — not a copy or summary of the textbook. Read the official chapter for the book's own text, activities and exercises.
This note's current text has no applied fact-check on record.
Mind map
Drawn from the same notes by a fixed rule (no AI): each label is the item's own words — its bold term, its label before a colon, a short formula as written, or its first words.
The mind map as a list
- Key ideas
- Blood is a fluid connective tissue…
- Erythrocytes carry haemoglobin…
- Human blood groups (ABO system)…
- The human heart is a four-chambered…
- One cardiac cycle (atrial systole
- The heart is myogenic
- An electrocardiograph (ECG) records…
- Formulas and facts
- Cardiac output (CO) = Stroke volume…
- Normal adult blood volume is about…
- Erythrocyte count
- Total leucocyte count
- Platelet count
- ABO compatibility rule
- Rh-negative mother carrying…
- Worked examples
- Calculating cardiac output after…
- Predicting transfusion compatibility
- Interpreting a simple ECG finding
- Watch out for
- Thinking arteries always carry…
- Confusing atrial and ventricular…
- Believing the brain controls every…
- Mixing up antigens and antibodies in…
- Assuming lymph and blood are identical
What this chapter is about
This chapter introduces the fluid connective tissues—blood and lymph—that transport materials throughout the human body, and the circulatory system that keeps these fluids in motion. You will learn the composition of blood, the types of blood cells, blood groups, and the mechanism of blood clotting. The chapter then moves to the structure of the human heart, the cardiac cycle, and how the heart generates and regulates its own beat.
Key ideas
- Blood is a fluid connective tissue containing plasma (about 55 %) and formed elements—erythrocytes (red blood cells), leucocytes (white blood cells) and thrombocytes (platelets).
- Erythrocytes carry haemoglobin, which binds oxygen reversibly; leucocytes defend the body; thrombocytes help in clotting.
- Human blood groups (ABO system) depend on the presence or absence of antigens A and B on RBC surfaces and the corresponding antibodies in plasma; the Rh factor adds another antigen (D).
- The human heart is a four-chambered muscular pump: two atria receive blood, two ventricles pump it out. The right side handles deoxygenated blood (to lungs), the left side oxygenated blood (to body).
- One cardiac cycle (atrial systole → ventricular systole → joint diastole) lasts about 0.8 s at rest, giving roughly 72 beats per minute; stroke volume is about 70 mL, so cardiac output ≈ 5 L/min.
- The heart is myogenic: the sinoatrial (SA) node generates impulses, which pass via the atrioventricular (AV) node and bundle of His to Purkinje fibres, ensuring coordinated contraction.
- An electrocardiograph (ECG) records the electrical activity as P wave (atrial depolarisation), QRS complex (ventricular depolarisation) and T wave (ventricular repolarisation).
- Lymph is tissue fluid that drains into lymphatic vessels, passes through lymph nodes, and returns to blood via large veins; it carries fats from the intestine and supports immunity.
Formulas and facts to remember
- Cardiac output (CO) = Stroke volume (SV) × Heart rate (HR). At rest: CO ≈ 70 mL × 72 beats/min ≈ 5 L/min.
- Normal adult blood volume is about 5–6 litres; plasma forms roughly 55 %, cells 45 % (haematocrit).
- Erythrocyte count: roughly 5 million per microlitre in males, 4.5 million in females.
- Total leucocyte count: 4 000–11 000 per microlitre; types include neutrophils, lymphocytes, monocytes, eosinophils and basophils.
- Platelet count: 1.5–4 lakh per microlitre; essential for clot formation via fibrinogen → fibrin conversion.
- ABO compatibility rule: a recipient should not receive blood with antigens against which they carry antibodies, else agglutination occurs.
- Rh-negative mother carrying Rh-positive foetus can develop anti-Rh antibodies; erythroblastosis fetalis may affect later pregnancies.
- Double circulation: blood passes through the heart twice in one complete circuit (pulmonary + systemic).
Common mistakes
- Thinking arteries always carry oxygenated blood → Pulmonary arteries carry deoxygenated blood from the heart to the lungs; define arteries by direction (away from heart), not oxygen content.
- Confusing atrial and ventricular systole → Atrial systole comes first and lasts about 0.1 s; ventricular systole follows and lasts about 0.3 s; keep the sequence clear.
- Believing the brain controls every heartbeat → The heart is myogenic; the SA node initiates beats automatically; the nervous system only modulates rate.
- Mixing up antigens and antibodies in blood groups → Antigens sit on RBC surfaces; antibodies float in plasma; a person does not carry antibodies against their own antigens.
- Assuming lymph and blood are identical → Lymph lacks RBCs and most proteins; it originates from tissue fluid and returns to blood via the thoracic duct.
Quick revision
- Blood = plasma + RBCs + WBCs + platelets; plasma is 55 % of blood volume.
- Heart: right side pumps to lungs, left side pumps to body; valves prevent backflow.
- SA node → AV node → bundle of His → Purkinje fibres: the conduction pathway.
- One cardiac cycle ≈ 0.8 s; CO = SV × HR; resting CO ≈ 5 L/min.
- ECG waves: P (atrial), QRS (ventricular depolarisation), T (ventricular repolarisation).
- Lymph drains tissue fluid, absorbs intestinal fats, and houses lymphocytes for immunity.