Page 112 - Headlines Histology2024_Neat

Medium-sized veins

• The tunica intima consists of endothelium rests on basal lamina. The
subendothelial layer is thin and consists of collagen and elastic fibers.

• The internal elastic lamina is absent.
• The tunica media is thinner than adventitia and consists of few layers of

smooth muscle cells.
• The tunica adventitia is much thicker than media composed of collagenous

fibers with few elastic fibers.
Large veins

• The tunica intima consists of endothelium and a prominent subendothelial
layer.

• The tunica media: is thin compared to the diameter of the lumen and consists
of a few layers of smooth muscle cells separated by bundles of collagen fibers.
Smooth muscle may be entirely absent.

• The tunica adventitia is the thickest layer and composed of longitudinally
arranged bundles of smooth muscle cells with collagen and elastic fibers.

Venous valves

• The veins of the extremities that are working against gravity are equipped with
valves.

• The valves are crescentic intimal folds consists of a connective tissue core
continuous with the subendothelial connective tissue covered on both sides by
endothelium.

• They prevent the backflow of blood in the opposite direction.

Arteriovenous anastomosis (A-V shunts)

• A-V Shunts are channels that provide direct communication between arterioles
and venules without passing in the capillary bed.

• They are similar to arterioles on their arterial side and similar to venules on
their venous side.

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