Page 422 - Atlas of Histology with Functional Correlations

STRUCTURAL PLAN OF ARTERIES

Wall consists of three layers: inner tunica intima, middle tunica media, and
outer tunica adventitia

Tunica intima consists of endothelium and subendothelial connective tissue
Tunica media is composed mainly of smooth muscle fibers with some elastic
fibers
In elastic and muscular arteries, smooth muscles produce elastic fibers and

some collagen
Tunica adventitia contains primarily collagen type I and elastic fibers
Internal elastic lamina (IEL) separates tunica intima from tunica media
Fenestrations in IEL allow diffusion of nutrients to deeper cells

External elastic lamina (EEL) separates tunica media from tunica adventitia

STRUCTURAL PLAN OF VEINS

Capillaries unite to form larger vessels called venules and postcapillary
venules
Thinner walls, larger diameters, and more structural variation than arteries
Blood under low pressure; valves are present to prevent backflow of blood in

extremities
Blood flow toward heart is due to muscular contractions around veins and
valves

Valves absent in veins of the viscera, the CNS, and the inferior and superior
venae cavae
Wall consists of three layers: tunica intima, tunica media, and tunica
adventitia
Tunica intima consists of endothelium and subendothelial connective tissue

Tunica media is thin, and smooth muscle intermixes with connective tissue
fibers
Tunica adventitia is the thickest layer, with longitudinal smooth muscle

fibers

VASA VASORUM

421