Heart and blood vessells презентация

anatomy

ARTERY
VEIN CAPILLARY

capillaries

blood away from the heart under fairly high pressure. These vessels branch into progressively thinner tubes and eventually give rise to fine branches called arterioles

innermost layer, tunica intima, is composed of simple squamous epithelium, called endothelium, resting on a connective tissue membrane, which is rich in elastic and collagen fibers. The middle layer, tunica media, makes up the bulk of the arterial wall. It includes smooth muscle fibers, which encircle the vessel, and a thick layer of elastic connective tissue. The outer layer, tunica adventitia, is relatively thin and consists chiefly of connective tissue with irregularly arranged elastic and collagen fibers. This layer attaches the artery to the surrounding tissues, be it muscle, adipose, or other tissue types

to form veins. The veins, which carry the blood back to the atria, follow pathways that roughly parallel those of the arteries.

The walls of veins are similar to those of arteries in that they are composed of three distinct layers. Because the middle layer of the venous wall is poorly developed, however, veins have thinner walls and contain less smooth muscle and less elastic tissue than comparable arteries.

Many veins, particularly those in the arms and legs, contain flaplike valves, which project inward from their linings. These valves are usually composed of two leaflets that close if the blood begins to back up in a vein. In other words, the valves aid in returning blood to the heart, since the valves open as long as the flow is toward the heart, but close if flow is in the opposite direction.