THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -Until recently, the endothelium was viewed simply as the boundary between the blood in the lumen and the walls of the vessels. Recent studies, however, have shown that it is physiologically critical to such activities as helping to regulate capillary exchange and altering blood flow.

Detailed explanation-2: -Each type of vessel has a lumen-a hollow passageway through which blood flows. Arteries have smaller lumens than veins, a characteristic that helps to maintain the pressure of blood moving through the system.

Detailed explanation-3: -In biology, a lumen (plural lumina) is the inside space of a tubular structure, such as an artery or intestine. It comes from Latin lumen ‘an opening’.

Detailed explanation-4: -Vessels that, when relaxed, measure <400 m in lumen diameter act as the major site of vascular resistance and include a network of small arteries (lumen ≈100 to 400 m) and arterioles (<100 m).