Circulatory System in Humans — Question 2
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Explain the process of blood circulation in the body with the help of a schematic diagram.
For completing one round of circulation in the body, the blood passes twice through the heart. This is called double circulation. Double circulation involves two processes: pulmonary circulation and systemic circulation.
Pulmonary circulation — The circulation of blood between the heart and lungs is called pulmonary circulation. From the right auricle, the blood flows into the right ventricle and then to the lungs through the pulmonary arteries. The oxygenated or pure blood from the lungs is brought to the left auricle by the pulmonary veins.
Systemic circulation — The circulation of blood between the heart and other body organs is called systemic circulation. From the left auricle, the oxygenated blood flows into the left ventricle and from there it is pumped into the aorta, the largest artery in the body. The aorta divides further to supply blood to all body tissues.
Below schematic diagram shows circulation of blood in the body:
Circulatory System – Interactive Study Guide
The circulatory system transports blood, oxygen, nutrients, and hormones throughout the body. It consists of the heart (pump), blood (transport medium), and blood vessels (pipelines).
Blood Components
| Component | Function | Key Fact |
|---|---|---|
| Plasma (55%) | Transports dissolved substances | 90% water, carries nutrients, hormones, waste |
| RBC | Carry oxygen | Biconcave disc, no nucleus, contain haemoglobin |
| WBC | Fight infections | Have nucleus, larger than RBC, immune defence |
| Platelets | Blood clotting | Cell fragments, no nucleus |
Blood Group Quick Reference
O = Universal Donor (no antigens) | AB = Universal Recipient (no antibodies)
| Group | Antigen | Antibody |
|---|---|---|
| A | A | anti-B |
| B | B | anti-A |
| AB | A & B | None |
| O | None | anti-A & anti-B |
Heart – Quick Facts
- 4 chambers: RA, RV, LA, LV
- 4 valves: Tricuspid (R), Bicuspid (L), 2 Semilunar
- Septum divides right (deoxy) from left (oxy)
- Left ventricle = thickest wall
Double Circulation
Pulmonary: RV → Pulmonary artery → Lungs → Pulmonary veins → LA
Systemic: LV → Aorta → Body → Vena cava → RA
Blood Vessels Comparison
| Arteries | Veins | Capillaries | |
|---|---|---|---|
| Direction | Away from heart | To heart | Connect A to V |
| Walls | Thick | Thin | 1 cell thick |
| Valves | No | Yes | No |
Self-Test Questions
- Why is the left ventricle wall thicker than the right?
- Draw and label the human heart.
- What is double circulation? Describe both circuits.
- Why is blood group O called universal donor?
- What is the function of valves in veins?