8. Microcirculatory blood system. Arterioles, venules, capillaries. Classification. Microscopic, ultra-microscopic and functional characteristics. Arteriovenous anastomoses.

Overview

The microcirculation is the smallest part of the vascular system, where blood meets the tissues. It consists of arterioles, capillaries and venules, with arteriovenous anastomoses that can bypass the capillary bed.

General structure of the vessel wall

• Vessel walls consist of 3 layers.

1. Tunica Intimia:

• The innermost layer.
• Lined by endothelium (comprised of simple squamous epithelial cells."

• Deep to the endothelium are a basement membrane, and a layer of subendothelial connective tissue.
• Has elastic membrane called internal elastic membrane at the boundary between the tunica intima and the tunica media.

Composed of elastic fibers, so it allows for elasticity facilitating the expansion and contraction d/ the cardiac cycle.

2. Tunica Media:

• The middle and thickest layer.
• Thicker in arteries than in veins.
• Consists of smooth muscle cells, collagen fibers and elastic fibers.
• External elastic membrane at the boundaries between tunica media and " "

3. Tunica Externa (adventita)

• The outermost layer.
• Composed of connective tissue arranged. longitudinally also with collagen and elastic fibers.

The C.T in the wall of veins is accompanied by smooth muscle cells.