Circulation V. Veins Regulation of Arterial Blood Pressure

Veins. Blood flows from the capillaries into the venules, small veins, large veins and into the right atrium. Some exchange of molecules occurs between the venules and the interstitial fluid. Most of the blood is in the veins. Blood reservoir.

The force driving the blood in the veins is the pressure difference between peripheral veins (5-10 torr) and the right atrium (0 torr). Veins are low resistance high capacitance (=compliance) vessels. Valves in veins allow flow in one direction.

Venous Valves

Walls contain smooth muscle innervated by sympathetic nerves that release NE. NE causes venoconstriction. Skeletal muscle pump. Respiratory pump.

Arterial Blood Pressure Regulation. Mean arterial blood pressure (MAP) has to be regulated to insure proper blood flow to tissues. High MAP  tissue damage. Low MAP  poor tissue perfusion. MAP = CO x TPR TPR = total peripheral resistance (sum of resistances of arterioles)

MAP = CO x TPR

MAP = CO x TPR. CO determines the rate at which blood goes into the art. system. TPR determines the rate at which blood leaves the art. system. MAP depends on volume of blood in the art. system.

Baroreceptor Reflex.

Arterial Baroreceptors Pressure receptors (stretch receptors). When blood pressure goes up the receptors are stretched and fire APs.

Carotid Sinus and Aortic Arch Receptors.

Effects of Gravity.