Human Heart: Structure & Function
The heart is a muscular organ which pumps blood to all parts of the body. Because both oxygen and carbon dioxide have to be transported by the blood, the heart has different chambers to prevent the oxygen-rich blood from mixing with the blood containing carbon dioxide. The human heart is roughly the size of a clenched fist.
Structure of the Heart
The heart is divided into four chambers:
- Atria (Upper Chambers): Thin-walled chambers that receive blood. There is a Left Atrium (LA) and a Right Atrium (RA).
- Ventricles (Lower Chambers): Thick-walled chambers that pump blood out with high pressure. There is a Left Ventricle (LV) and a Right Ventricle (RV).
- Septum: A dividing wall that separates the left (oxygenated) side from the right (deoxygenated) side.
- Valves: Ensure that blood does not flow backward when the atria or ventricles contract.
(Blue = Deoxygenated blood, Red = Oxygenated blood)
Circulation of Blood (Double Circulation)
In humans, blood flows through the heart twice during each cycle. This is called Double Circulation.
1. Pulmonary Circulation (Lungs)
Deoxygenated blood from the body enters the Right Atrium, moves to the Right Ventricle, and is pumped to the lungs via pulmonary arteries for oxygenation.
2. Systemic Circulation (Body)
Oxygenated blood from the lungs enters the Left Atrium, moves to the Left Ventricle, and is pumped to the rest of the body via the Aorta (main artery).
Blood Vessels: Arteries vs Veins
| Arteries | Veins |
|---|---|
| Carry blood away from the heart. | Carry blood towards the heart. |
| Thick, elastic walls (high pressure). | Thin walls (low pressure). |
| Do not have valves. | Have valves to ensure one-way flow. |
| Carry oxygenated blood (Except Pulmonary Artery). | Carry deoxygenated blood (Except Pulmonary Vein). |
- Left Ventricle has the thickest muscular wall because it pumps blood to the whole body.
- Separation of right and left sides is essential for birds and mammals to maintain high energy needs and body temperature.
- Fish have only a 2-chambered heart and single circulation.
Chapter Assessment
1. Why is it necessary to separate oxygenated and deoxygenated blood in mammals?
2. Describe the double circulation in human beings.
3. What is the function of valves in the heart?
Last Updated: January 2026
Reviewed under Sarkari Service Prep Academic Policy.
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