Page 8 - class-XI-ch.8-Lesson notes

Veins

The veins return the blood to the heart. The structure of the veins is similar to that of arteries. These veins tend to
collapse when not filled with blood. In general, the total diameter of the veins returning blood from any organ is at
least twice the diameter of the arteries carrying blood to the organ. The veins of lower limbs have greater number of
valves than those of the upper limbs. These valves are not found in many veins.
Capillaries
The capillaries are minute vessels that connect the arterioles with the venules.

Types of Capillaries
There are three types of capillaries.

(a) Continuous Capillaries: These are found in all types of muscles, in connective tissue and in the central
nervous system.
(b) Fenestrated Capillaries: These are found in renal organ, endocrine glands and in intestines.

(c) Sinusoidal Capillaries: These are enlarged capillaries found in the liver, spleen and bone marrow.

Function of Capillaries
In the capillaries, exchange of materials takes place. It has been estimated that there are about 7,000 sq meters of
blood capillaries in an adult's body. This is, indeed, a large area for exchange of substances between the blood and
the tissue fluid. In the glandular organs, the capillaries supply the substances required for secretion; in the
alimentary canal, they take up some of the digested food; in the lungs, they get oxygen and give up C02', in the
kidneys, they discharge the waste products collected from other parts. Every time, everywhere in the body and
walls, an interchange is going on through their walls which is essential for the life of the body.

Functions of Circulatory System

The primary function of the blood circulatory system is to ensure the preservation of the constant internal

environment by transporting oxygen, food material and hormones to the tissue cells and by remo As a matter of
fact, different organs, including blood, perform different functions, which are as follows.

1, Heart works like a pump, which circulates the blood throughout the body.

2. Arteries allow the pure blood to pass through them throughout the body.
3. Veins bring the impure blood to the heart from every part of the body.
4. In capillaries, the exchange of nutrients, oxygen and waste products takes place.
5. Blood carries body oxygen to the from lungs. The lungs to different parts of the body and C02 from the cells of

the body to the lungs.
6. Blood carries digested food or nutrients to all parts of the body.

7. Blood carries hormones from the endocrine glands to different organs of the body.
8. Blood carries waste products like urea, lactic acid, uric acid, sulphates, etc., to the kidneys for excretion.
9. Blood regulates the body temperature.

EQUILIBRIUM—DYNAMIC AND STATIC AND CENTRE OF GRAVITY
AND THEIR APPLICATION IN SPORTS

Equilibrium

When all the forces acting on the body are counterbalanced by equal and opposite forces, so that the sum of the forces
equals zero, it is called the state of equilibrium. It can also be said that equilibrium occurs when the resultant force
acting on a point is zero, i.e., the vector sum of all forces is zero. A state of equilibrium occurs when the body’s centre of