Blood vesels

The blood vessels are the tubes through which flows the blood. There are mainly three types of blood vessels:

• The arteries are the blood vessels leading from the heart. It has elastic and resistant walls, as well as a powerful muscular layer that regulates the pressure with which the blood leaves the heart. With ventricular systole, blood leaves the heart filling the artery and the sigmoid valves close so that it cannot back up .

The arteries are made up of three layers, the muscular layer being very thick since its contractions help drive the blood.

The arteries, as they move away from the heart, branch into other thinner and less elastic vessels called arterioles.

By Kelvinsong (Own work) [CC BY-SA 3.0], via Wikimedia Commons

• The capillaries are extremely fine vessels (so called capillaries, to be as thin as hairs) arising from the ramifications of arterioles, which carry blood to all cells of the body .

Its wall is very thin, made up of a single layer of flat cells (called the endothelium ), which allows substances from the blood to pass into the cells and their waste into the blood. It is in the capillaries where the exchange of substances between the blood and the interstitial plasma takes place .

The capillaries reach all the cells of the organs, since we have several million blood vessels, about 100,000 km long.

Activity: Blood vessels.

Activity: Crossword on blood vessels.

Experiments with your body: Blood.

Activity: Blood vessels.

• Capillaries join to form venules, which group together to form veins, the blood vessels that carry blood to the heart. Its wall is thinner (its muscular layer is smaller) and less resistant than that of the arteries, since the blood circulates through them with less pressure. Instead, they have a larger diameter than arteries because their wall is compliant, with a greater capacity to accumulate blood. Inside they have valves, called venous valves that prevent the backward movement of blood and promote its movement towards the heart.