Vasa vasorum are blood vessels serving the adventitia and media of larger arteries and veins. Portal systems exist to the liver and pituitary gland, where venous blood drained from one organ is fed as a supply to the sinusoids or capillaries of another. Sinusoids may take the place of a capillary bed. Venous sinuses are endothelium-lined CT spaces where blood can collect for purposes other than metabolic exchange, thus, as part of the venous collecting system, e.g, coronary and dural sinuses, and in erectile tissue. 9 Morphology in relation to physical factors in various vessels of the system Large elastic or conducting arteries - collagen fibres and elastic laminae predominate for strength, and elastic distensibility provides for elastic recoil during diastole thus damping the pulsatile flow resulting from the intermittent contractions of the heart.
Endothelium provides a smooth lining to facilitate flow and prevent clotting.
In general, elastic is not needed for recoil, for variations in pressure between diastole and systole are insignificant, but the vena cava has significant numbers of elastic fibres. Tricuspid Valve . . . . . Annuli fibrosi . . . . . Pulmonary Valve . . . . . Annuli fibrosi . . . .