Question

If the vascular resistance in blood vessels increases blood pressure why do veins have very little pressure?

Answer 1

Answer:

Blood is the only liquid connective tissue of our body. It needs to be circulated within the different body parts as it carries and transports the different nutrients, gases and many other substances which are required by us and also performs a number of important functions.

Humans have a closed circulatory system and the blood within the body flows through the arteries and veins.

A few points depicting the differences between the arteries and veins are as mentioned below:

1. Arteries carries pure oxygenated blood whereas, veins carry impure deoxygenated blood
2. The blood pressure within the arteries is high whereas the blood pressure within the veins is less
3. Since the blood pressure is high within the arteries, they do not have valves. Whereas since the blood pressure within the veins is low, they do not have valves so as to prevent the back flow of the blood
4. The walls of the arteries are thick and the walls of the veins are comparatively thinner.

Thus, from the above mentioned points of differences, it becomes clear that the blood pressure within veins is less.

The prime reason for this is accountable due to their distant location.

Mean arterial pressure is defined as the average pressure exerted by the walls of the arteries during the completion of a single cardiac cycle; that is contraction and relaxation of the heart.

After a single cardiac cycle gets over; 70 ml of the blood; which is also called as the stroke volume enters into the aorta; which is the longest artery and hence gets distributed among the different body parts. Since, arteries lie closer to the heart; a high blood pressure is exerted on them. Also, the walls of the arteries have immense elasticity due to which the increased resistance to the blood flow is maintained.

Whereas, after the tissue metabolism gets over, carbon dioxide gets released and they get mixed with the blood. Also they are distantly located from the heart. Thus, as the distance from the heart increases, the mean arterial pressure decreases and hence the blood pressure is less within the veins as compared to the arteries. Also, the walls of the veins are comparatively thinner and hence also become a contributing factor towards the low blood pressure within them.