Blood Vessels

Flow of Blood through Blood Vessels Heart Artery Arterioles Capillaries Venule Vein

Arterial System

Arterioles the major determinant of blood pressure The major determinant of blood flow to the individual organs. Blood flow to individual organs can be regulated by controlling the diameter of the arterioles. Vasodilation lowers resistance Vasoconstriction increases resistance and results in decreased flow through that particular arteriole.

Arteries vs Arterioles

Capillaries

Veins Larger and more compliant (stretchable) than arteries Hold more blood. Containing 60% of the total blood volume at rest. As physical activity: vasoconstriction, driving more blood back to the heart and increasing circulation. one-way valves that insure unidirectional flow of blood.

Skeletal muscle pump. Veins pass between skeletal muscles. The contraction of skeletal muscle squeezes the vein, thus increasing blood pressure in that section of the vein. Pressure causes the upstream valve (furthest from the heart) to close and the downstream valve (the one closest to the heart) to open. Repeated cycles of contraction and relaxation, as occurs in the leg muscles while walking, effectively pumps blood back to the heart.

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Fig. 20.8

Varicose Veins

Systemic Blood Pressure

Arterial BP “Normal” BP = 120/80 Hg/mm Systolic pressure- ventricles contract- Aortic valve open – Peak pressure Diastolic Pressure: ventricle relax- aortic valve closed- lowest pressure MAP= - mean arterial pressure- pressure that pushes blood into tissues MAP = diastolic + (pulse pressure/3)

Regulation Of BP 2. Peripheral resistance 3. Blood Volume Cardiac Output = heart rate) X stroke volume An average person has a resting heart rate of 70 beats/minute and a resting stroke volume of 70 mL/beat. The total volume 5 liters (5000 mL). According to our calculations, the entire volume of blood within the circulatory sytem is pumped by the heart each minute (at rest). During vigorous exercise, the cardiac output can increase up to 7 fold (35 liters/minute) 1 Cardiac Output 2. Peripheral resistance 3. Blood Volume

Starling's Law Describes the relationship between end-diastolic volume and stroke volume. The heart will pump out whatever volume is delivered to it. If the end-diastolic volume doubles then stroke volume will double

Baroreceptors- Neural Control

Hormonal Control

ADH and Aldosterone Aldosterone released by adrenal gland Sodium reabsorbed in kidney Water reabsorption by kidneys Increased blood volume

Control of Heart Rate SA node: controlled by sympathetic and parasympathetic nerve fibers. 1. At rest: the parasympathetic fibers release acetylcholine, which slow the pacemaker. 2. Activity (physical or emotional) sympathetic nerve fibers release norepinephrine and Epinephrine which acts to speed up the SA node thus increasing heart rate.

Blood Flow Capillaries- Blood Volume

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