BIOLOGY [5 Mark Question Answer]

The three kind of blood vessels found in human beings are arteries, veins and capillaries

1. Arteries are the blood vessels that carry blood from the heart to the various parts of the body.
2. Veins are the blood vessels that carry blood from the body parts to the heart
3. Capillaries: These are the terminal branches of an artery, which rejoin to form a vein. A capillary is a very narrow tube whose walls have a single layer of cells with no muscles. Although the wall of a capillary is very thin, yet an exchange of nutrients, waste products and gases take place between the blood and the body fluids.

Differences:

Arteries

1. Carry blood away from the heart.
2. Have thick and more muscular walls.
3. Carry oxygenated blood (except pulmonary artery which carries deoxygenated blood).
4. The blood flows with jerks and under great force.

Veins

1. Carry blood towards the heart.
2. Have thin and less muscular walls.
3. Carry deoxygenated blood (except pulmonary vein which carries oxygenated blood).
4. The blood flows smoothly and under little pressure

Capillaries

1. Arteries after entering an organ divide into number of smaller branches called arterioles which further divide repeatedly to form a network of fine branches called capillaries.
2. The walls of the capillaries are very thin and are one cell deep.
3. The Capillaries after the metabolic exchange unite to form larger vessels called venules, which again unite to form a vein.

The circulation of blood through the human heart takes place twice making one complete round through the body. This is called double circulation. The impure blood (deoxygenated blood) is collected from different body organs through two major veins (vena cava). The two veins empty blood into the right auricle. From here, it enters the right ventricle and is carried to lungs by pulmonary artery. Exchange of gases takes place in the lungs. Pulmonary vein then carries the pure (oxygenated) blood to the left auricle. From here, it enters the left ventricle and is then carried by an artery called aorta to all parts of the body.Double circulation can be summarised as:Circulation of blood between the heart and the lungs is called pulmonary circulation.
In this, the blood flows as follows:
Right ventricle → lungs → left auricle (through pulmonary veins)Circulation of blood between the heart and body organs (except lung) is called systemic (body) circulation.
Blood flows as following:
Left ventricle → body organs → right auricle (through vena cava)