Body Fluids and Circulation

REVISION SUMMARY: Body Fluids and Circulation (NCERT Class 11)

1. Chapter at a Glance

• Blood is a special connective tissue consisting of fluid matrix (plasma) and formed elements (RBCs, WBCs, platelets).
• Plasma constitutes ~55% of blood (90-92% water + 6-8% proteins: fibrinogen, globulins, albumins); formed elements constitute ~45%.
• RBCs (erythrocytes): 5–5.5 million mm⁻³, biconcave, anucleate in mammals, contain haemoglobin (12–16 g/100 ml blood), lifespan 120 days (destroyed in spleen).
• WBCs (leucocytes): 6000–8000 mm⁻³; granulocytes (neutrophils 60–65%, eosinophils 2–3%, basophils 0.5–1%) and agranulocytes (lymphocytes 20–25%, monocytes 6–8%).
• Platelets (thrombocytes): 1.5–3.5 lakh mm⁻³; involved in blood coagulation.
• ABO and Rh blood grouping based on surface antigens on RBCs; universal donor O, universal recipient AB.
• Lymph (tissue fluid) is colourless, collected by lymphatic system; carries nutrients, hormones, fats (via lacteals).
• Heart is myogenic (autoexcitable nodal tissue); SAN acts as pacemaker (70–75 action potentials min⁻¹).
• Cardiac cycle: 0.8 s duration; stroke volume ~70 ml; cardiac output ~5 L min⁻¹ (double circulation: pulmonary + systemic).
• ECG records electrical activity (P-wave: atrial depolarisation; QRS: ventricular depolarisation; T-wave: ventricular repolarisation).

2. Definitions and Laws (exact NCERT framing)

• “Blood is a special connective tissue consisting of a fluid matrix, plasma, and formed elements.”
• “Plasma without the clotting factors is called serum.”
• “Erythrocytes or red blood cells (RBC) are the most abundant of all the cells in blood.”
• “Leucocytes are also known as white blood cells (WBC).”
• “Platelets also called thrombocytes, are cell fragments produced from megakaryocytes.”
• “The fluid present in the lymphatic system is called the lymph.”
• “Heart is called myogenic.”
• “Sino-atrial node (SAN)… is called the pacemaker.”
• “This sequential event in the heart which is cyclically repeated is called the cardiac cycle.”
• “The stroke volume multiplied by the heart rate gives the cardiac output.”
• “Cardiac output can be defined as the volume of blood pumped out by each ventricle per minute.”
• “Normal activities of the heart are regulated intrinsically… hence the heart is called myogenic.”
• “Hypertension is the term for blood pressure that is higher than normal (120/80)… 140/90 or higher shows hypertension.”
• “Heart failure means the state of heart when it is not pumping blood effectively enough to meet the needs of the body.”

3. Important Diagrams and Activities

• Figure 15.1: Diagrammatic representation of formed elements in blood – shows RBC, platelets, and all types of WBCs with relative abundance.
• Figure 15.2: Section of a human heart – shows four chambers, septa, valves (tricuspid, bicuspid, semilunar), SAN, AVN, AV bundle and Purkinje fibres.
• Figure 15.3: Diagrammatic presentation of a standard ECG – shows P, QRS and T waves with their correspondence to electrical events.
• Figure 15.4: Schematic plan of blood circulation in human – shows pulmonary and systemic circuits, hepatic portal system and coronary circulation.

4. Common Misconceptions and Exam Pitfalls

• Do not confuse “single circulation” (fishes) with “incomplete double circulation” (amphibians/reptiles) – only birds/mammals have complete double circulation with no mixing.
• Rh incompatibility (erythroblastosis foetalis) occurs only in Rh–ve mother with Rh+ve foetus and usually affects subsequent pregnancies, not the first.
• Cardiac output is volume per ventricle per minute (not total); normal value is 5 litres.
• Heart sounds: “lub” = closure of AV valves (tricuspid + bicuspid); “dub” = closure of semilunar valves.
• Hypertension threshold is exactly 140/90 mm Hg as per NCERT; do not use other values.
• SAN generates 70–75 min⁻¹; average heart rate given as 72 beats min⁻¹.

5. Formula Sheet