The flow of blood through the heart:
- Oxygen-rich blood reaches the thin-walled upper chamber of the heart on the left, the left atrium from the lungs. The left atrium relaxes and collects blood; then contracts to enter the next chamber (the left ventricle), which expands so blood gets collected into it. The muscular ventricle contracts and pumps oxygen-rich blood to all parts of the body.
- Deoxygenated blood from the body comes to the upper chamber on the right side (the right atrium), and it expands. As the right atrium contracts, the corresponding lower chamber (the right ventricle) relaxes. This transfers blood to the right ventricle which in turn pumps into the lungs for oxygenation. This process is repeated continuously to fulfil the oxygen needs of the body.
The blood circulatory system in humans is double circulation as blood reaches the heart twice in one complete cycle.
- The pathway of blood from the heart to the lungs and back to the heart is called pulmonary circulation.
- The pathway of blood from the heart to the rest of the body and back to the heart is called systemic circulation.
- Systemic Circulation + Pulmonary Circulation = Double Circulation
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