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 MAPtissue 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.