Human Anatomy — Circulatory System
Introduction
The circulatory system transports blood, oxygen, nutrients, and wastes throughout the body. In ICSE Class 10 Biology, you study the structure of the heart, the pathway of blood circulation, the types of blood vessels, and the composition of blood.
Human Heart Structure
The heart is a muscular organ located in the chest cavity between the lungs.
| Chamber | Position | Function |
|---|---|---|
| Right atrium (RA) | Upper right | Receives deoxygenated blood from body via vena cava |
| Right ventricle (RV) | Lower right | Pumps deoxygenated blood to lungs via pulmonary artery |
| Left atrium (LA) | Upper left | Receives oxygenated blood from lungs via pulmonary vein |
| Left ventricle (LV) | Lower left | Pumps oxygenated blood to body via aorta |
Valves of the Heart
| Valve | Location | Function |
|---|---|---|
| Tricuspid valve | Between RA and RV | Prevents backflow into RA |
| Bicuspid (mitral) valve | Between LA and LV | Prevents backflow into LA |
| Semilunar valves | Aorta and pulmonary artery exits | Prevent backflow into ventricles |
Double Circulation
The human heart pumps blood through two separate circuits.
Pulmonary Circulation
Right ventricle → Pulmonary artery → Lungs → Pulmonary vein → Left atrium (Deoxygenated blood becomes oxygenated in the lungs)
Systemic Circulation
Left ventricle → Aorta → Body tissues → Vena cava → Right atrium (Oxygenated blood delivers O₂ to tissues; deoxygenated blood returns)
Advantage: Complete separation of oxygenated and deoxygenated blood ensures efficient oxygen delivery.
Blood Vessels
| Vessel | Structure | Function |
|---|---|---|
| Arteries | Thick, muscular, elastic walls; no valves | Carry blood AWAY from the heart (usually oxygenated) |
| Veins | Thin walls, valves present | Carry blood TOWARDS the heart (usually deoxygenated) |
| Capillaries | One-cell thick walls | Exchange of nutrients, gases, and wastes with tissues |
Blood Components
| Component | Percentage | Function |
|---|---|---|
| Plasma | 55% | Liquid matrix — carries nutrients, hormones, wastes |
| Red blood cells (RBCs) | 44% | Transport oxygen (contain haemoglobin); no nucleus |
| White blood cells (WBCs) | <1% | Immunity — fight infections (neutrophils, lymphocytes, etc.) |
| Platelets | <1% | Blood clotting — release thromboplastin |
Blood Clotting Mechanism
- Injury exposes platelets to damaged tissue.
- Platelets release thromboplastin.
- Thromboplastin converts prothrombin → thrombin (in presence of Ca²⁺ and vitamin K).
- Thrombin converts fibrinogen → fibrin.
- Fibrin forms a mesh that traps RBCs, forming a clot.
Common Heart Conditions
| Condition | Description |
|---|---|
| Heart attack (myocardial infarction) | Blockage in coronary artery interrupts blood supply to heart muscle |
| Hypertension | High blood pressure (above 140/90 mm Hg) |
| Stroke | Blockage or rupture of blood vessel in the brain |
Common Mistakes and Fixes
| Mistake | Fix |
|---|---|
| Confusing pulmonary artery and pulmonary vein | Pulmonary artery carries DEOXYGENATED blood (to lungs) — exception to the rule |
| Thinking the right side has oxygenated blood | Right side = deoxygenated; Left side = oxygenated |
| Forgetting valves are in veins only | Arteries do NOT have valves (high pressure keeps blood flowing) |
| Calling RBCs 'cells' when they lack a nucleus in humans | RBCs are anucleate in mammals |
ICSE Exam Focus
This chapter carries 6–8 marks. Key topics: heart structure (labelled diagram), double circulation pathway, blood components and functions, clotting mechanism.
Marks Blueprint: Heart structure — 2 marks, Double circulation — 2 marks, Blood components — 2 marks, Clotting mechanism — 2 marks.
Self-Test Questions
-
Draw a labelled diagram of the human heart showing the four chambers and valves.
-
What is double circulation? Explain the pulmonary and systemic circuits.
-
Distinguish between arteries and veins (at least four differences).
-
List the components of blood and state one function of each.
-
Explain the process of blood clotting.
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Why is the wall of the left ventricle thicker than that of the right ventricle?
