What one structural feature do all blood capillaries have in common -
Ans. is None The blood flows from the hea through aery, aeriole, capillary, venule and vein, and then returns to the hea. Structure of aery and aeriole o It is made up three layers ? Tunica Intima o The inner most layer (towards lumen) of aery is intima. o It consists of endothelial cells which rest on basment membrane. o There is some subendothelial connective tissue. o Intima is separated from media by internal elastic lamina. Tunica Media o It is mainly contains smooth muscles and laminae of elastic tissue Media is separated from adventitia by external elastic lamina. Tunica Adyentitia o It is the outer most layer. o Contains collegen and elastic fibers. Structure of capillaries o Capillaries are thin walled vessels made up of single layer of endothelial cells with its basement membrane. o Capillaries are of three types ? Continous capillaries ? o These capillaries has continuous lining of endothelial cells with no fenestration. o Basement membrane is also continuous. Fenesterated capillaries o There are fenestration between the endothelial cells. o Basment membrane is continuous. Sinusoidal capillaries o Both endothelial cells and basement membrane have fenestration. o In resting tissues, most of the capillaries are collapsed and blood flows through the throughfare vessels from the aerioles to the venules. Structure of veins o Structure of vein is smiliar to aery except that ? 1.Wall is thinner Three tunicae are less well demarcated. Elastic tissue is scanty and not clearly organized into distinct internal and external elastic lamina. 4.Have valves (except venae cavae and common iliac vein). Note ? For one option go ahead with option d i.e continuous basement membrane, because the term capillary is used generally for the first two types of capillary (both have continuous basment membrane). The third type of capillary (sinusoidal capillary) is usually referred as sinusoid, e.g. liver sinusoid, splenic sinusoid.
Absence of intracellular fenestrations in the endothelial cells
Presence of intracellular fenestrations
A discontinuous basement membrane
None