In this article we will discuss about the general features of Arteries and Veins.
Arteries and veins are main blood vessels. Arteries carry blood from the heart to different body parts. Veins bring blood from different body parts to the heart. The veins have valves to prevent backward flow of blood. In the organs both arteries and veins divide to form arterioles and venules respectively.
The arterioles and venules further divide into the thin walled vessels called capillaries. The capillaries of arteries and veins are united. The nutrients, hormones, gases, etc. can diffuse into the tissue cells through the walls of the capillaries and vice versa. Thus arteries, arterioles, capillaries, venules and veins are blood vessels.
The wall of an artery and a vein consists of three coats:
(i) Tunica externa:
It is the outermost coat which is formed of connective tissues. Tunica externa is also called tunica adventitia.
(ii) Tunica media:
It is a middle coat which is chiefly formed of elastic connective tissue and smooth muscle fibres. It is thicker in artery.
(iii) Tunica interna (= tunica intima):
It is the innermost coat which is made up of two parts:
(a) Elastic membrane:
This membrane is made up of elastic tissue of yellow fibres. It is thicker in artery.
It is made up of flattened squamous epithelial cells lining the lumen. Its cells are more elongated in artery. Blood capillaries consist of endothelium only.