120 Over 80 Articles - Capillaries

Cardiovascular System
Capillaries

Capillaries are the smallest of all the body's blood vessels, that connect the smallest arteries (called arterioles), to the smallest veins (called venules), in a web-like network reaching all peripherals of the body.
So extensive is this network of a billion or so capillaries in the body, that their total surface area is about 1100 square miles.

The capillary walls compose of only a single layer of cells, called Endothelium. This layer is so thin and permeable that molecules of oxygen, water, and the base constituents of food (all present in the blood) pass through them by diffusion and enter cells of tissue that are close by. Waste matter from the cellular chemical reactions such as carbon dioxide, easily diffuse back across the capillary walls into the blood to be transported for removal via venules.

The blood flows across the capillaries in the "arterioles-to-venules" direction because the blood pressure in these tiny arterioles is about 50 times that in the venules. The pressure difference causes the movement.

Capillaries also help to release excess heat from the body. During exercise, for example, the body and blood temperature rises. To help dissipate this excess heat, the blood delivers the heat to the capillaries, which then rapidly release it to the tissue. The capillaries near the skin will may well become flushed or change colour while the excess heat situation continues.

Effect on High Blood pressure

With regard to high blood pressure and hypertension it is interesting to note that 1-pound of body fat is riddled with about five miles of capillaries in order for the body to maintain it.
It is thus obvious that the heart, in pumping blood for this ‘extra’ peripheral requirement, works harder therefore we should not under-estimate the overhead imposed on the cardiovascular system if one ‘gains only a few pounds’ in weight.
This mechanical explanation explains why high blood pressure tends to fall dramatically when overweight people shed excess weight.

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