Page 16 - Viva ICSE Science 5 : E-book

Structure left
aorta
auricle
The human heart is four-chambered—two upper right
chambers called the auricles and two lower auricle

chambers called the ventricles. Auricles receive valves
blood from the body, while ventricles pump right
ventricle
blood throughout the body. The heart is divided
partition
vertically into two parts by a muscular wall. Each completely left

half comprises of an auricle and a ventricle divided separating the ventricle
two halves
by a valve. The valves allow the fl ow of blood in one
Human heart (simplifi ed section)
direction only.

Functions

The main function of the heart is the circulation of blood. It pumps pure blood, i.e.,
blood rich in oxygen to all parts of the body and receives impure blood, i.e., blood
containing carbon dioxide from the body. It also pumps the impure blood to the lungs

for purifi cation.

While pumping blood, the heart makes a rhythmic movement which is called the
heartbeat. This movement can be felt at several points of our body like the forehead,

neck and the wrist. The light movement of the blood vessels felt at these points is called
the pulse, and the number of pulse that can be felt in a minute makes the pulse rate. The

average pulse rate of an adult human being is 72 times per minute.

When you visit a doctor, he often holds your wrist and counts something. He is, in fact,
counting your pulse rate by feeling the pressure of the movement of blood through the

blood vessel in your wrist.

Blood

Blood is a red-coloured fl uid which fl ows inside the blood vessels. It consists of a liquid
part and a number of cells of diff erent kinds which are present in the liquid.

There are three types of cells present in the blood.

• Red blood cells (RBCs)

• White blood cells (WBCs)

• Platelets

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