What is Circulatory System?

All parts of the body require nourishment and oxygen. At the same time waste products need to be removed from all the cells in the body. These and many other functions in the body are carried out by the circulatory system. The circulatory system consists of:

The Circulatory System

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  1. Heart
  2. Blood Vessels
  3. Blood

1. Heart:

Heart is a hollow-pumping organ, made up of special muscle fibers which never get tired. It is located in the chest cavity slightly titled towards the left. The size of the heart is almost the size of your closed fist. The heart of average adult weights about 300 grams.

Heart is divided into two equal halves by a muscular partition. Each half is further divided into two chambers. The upper chambers of both the halves are called auricles. The lower chambers are called ventricles. Auricle of each side opens into the ventricle of the same side. The right side of the heart receives carbon dioxide rich blood (deoxygenated blood) from all parts of the body and sends it to lungs for oxygenation. The left side of the heart receives oxygen-rich blood (oxygenated blood) from the lungs and sends it for distribution to rest of the body.


Heartbeat: Place your ear on your friend’s cheat. Do you hear a thumping sound? These sounds are the heart beats. Heart contracts and expands repeatedly in order to pump blood in the blood vessels. Count the number of times the heart beats in a minute. When you are at rest, your heart beats about 70 times in a minute. Ask your friend to run for a while and again count the beats in a minute. You will notice that the heartbeat increases considerably after exercise- sometimes three times faster to send more oxygen and nutrients to your hardworking muscles. When you sleep your heartbeats are slower since your muscles need less oxygen. The human heart pumps about 5 liters of blood per minute in resting state. This may rise to even 20 liters per minute in strenuous exercise.

Pulse: As the heart beats it sends waves along the arteries. Thus the pulse rate may be counted to know the rate of heart beat. Pulse can be feeling wherever arteries are close to the skin as in the wrist and the temple region. The heart rate increases during exercise, fever and emotions like anger and fear. That is how a doctor can tell whether you are sick or not by counting your pulse rate.

2. Blood Vessels:

Circulation of blood in the human body takes place in closed vessels. This was first discovered by William Harvey, an English physiologist. The blood vessels are of three kinds:

  • Arteries: They carry oxygenated blood from heart to different parts of the body. They have thick walls and are present deep inside the tissues of the body.
  • Veins: They return the deoxygenated blood from different parts of the body to the heart. They are thin walled and lie quite close to the skin. Observe your hands and feet carefully. Do you see some bluish lines running just beneath the skin? These blue lines are the veins.
  • Capillaries: The arteries branch into very fine blood vessels called capillaries which form a fine network in the tissues. These capillaries join at the other end to form veins. Arteries and veins are thus connected to each other by capillaries.

3. Blood

It is a thick red-colored fluid. An average person has about 6.5 liters of blood in his body. Blood consists of a fluid base called plasma in which float three kinds of blood cells- the red blood cells (RBC), white blood cells (WBC and platelets.


Functions of Blood:

  • Blood transports oxygen, food, hormones and metabolites to all parts of the body.
  • It collects carbon dioxide and other waste products from the body cells and carries them to the organs of excretion.
  • It helps to maintain a constant body temperature.
  • It protects the body against infections.
  • It prevents its loss in injury by clotting.
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