To permit material exchange between blood and tissues.
Because capillaries are very thin. many times as few as one red blood cell wide, and only have enough room for a layer of endothelial tissue, in the form of the Tunica Intima.
Tunica Adventitia. Tunica media, Tunica intima
The tunica media is thicker in arteries than in veins.
Intra (Tunica intima) - simple squamous Media (Tunica media) - Fibrous Connective Tissue (FCT) Externa (Tunica adventitia) Fibrous Connective Tissue (FCT)
they help the vein to stretch to prevent over expansion
The tunica media of arteries is larger than that of veins of same size.The tunica adventitia is larger in veins than arteries of same size.
The tunica intima is the innermost layer containing mostly endothelium, the one through which the lumen runs. Surrounding this is tunica media which mostly muscle tissue. And finally surrounding this is the outermost layer, the tunica adventitia which is mostly connective tissue.
large veins have narrow tunica intima.and tunica media consist of many layers of smooth muscle which are separated by collagenous connective tissue,and have very few elastic fibers.tunica adventitia is broad,and formed by collagen,tunica adventitia have vasa vasorum.example is femoral and renal vein. in medium size veins tunica intima is a bit more then endothelial call.and have fibrous supporting layer.tunica media is composed of 2 to 4 layers of smooth muscle fibers.tunica adventitia is thick layer and made up of collagen fibers. ........................... maniba ,hebei united medical university tangshen ,,hebei .,,,china
precapillary sphincters
A thin inner layer, a muscular middle layer (that gives the vessel its flexibility under pressure from the filling blood), and a fiber-like outer layer that gives the vessel strength to not burst when the heart pumps blood to the body.
Tunica Media
The middle layer of a vein is called the tunica media. It is made of circularly arranged smooth muscle and connective tissue (with a lot of elastin and collagen).