The circulatory system transports blood, oxygen, nutrients and waste throughout the body. The heart and blood vessels are favourite topics in competitive biology.
The Heart
The human heart has four chambers: two atria (upper) and two ventricles (lower). It is located in the chest and is about the size of a fist. It acts as a pump for blood.
Blood Vessels
- Arteries: carry blood away from the heart; usually oxygen-rich.
- Veins: carry blood towards the heart; usually oxygen-poor.
- Capillaries: thin vessels where exchange of gases happens.
Double Circulation
Human blood passes through the heart twice in one cycle, called double circulation. Pulmonary circulation carries blood between the heart and lungs. Systemic circulation carries blood between the heart and the rest of the body.
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Blood
- RBCs: carry oxygen using haemoglobin.
- WBCs: fight infection.
- Platelets: help in clotting.
- Plasma: liquid part of blood.
Blood Pressure
Normal blood pressure is about 120/80 mm Hg. The higher value is systolic (heart contracts) and the lower is diastolic (heart relaxes). Blood pressure is measured with a sphygmomanometer.
Quick Revision Points
- The heart has four chambers.
- Arteries carry blood away from the heart.
- Haemoglobin in RBCs carries oxygen.
- Normal BP is 120/80 mm Hg.
- BP is measured by a sphygmomanometer.
- Humans show double circulation.
- Platelets help in blood clotting.