Concepts of Human Anatomy & Physiology   5/e   Van De Graaff/Fox
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I. Cardiac Output

Concept: The pumping ability of the heart is a function of the number of beats per minute (cardiac rate) and the volume of blood ejected per beat (stroke volume). The cardiac rate and stroke volume are regulated by autonomic nerves and by mechanisms intrinsic to the cardiovascular system.

II. Blood Volume

Concept: Fluid in the extracellular environment of the body is distributed between the blood and the tissue fluid compartments by filtration and osmotic forces acting across the walls of capillaries. The function of the kidneys influences blood volume because urine is derived from blood plasma. The hormones ADH and aldosterone act on the kidneys to help regulate the blood volume.

III. Vascular Resistance to Blood Flow

Concept: The rate of blood flow to an organ is dependent on the resistance to flow in the small arteries and arterioles that serve the organ. Vasodilation decreases resistance and increases flow, whereas vasoconstriction increases resistance and decreases flow. Vasodilation and vasoconstriction occur in response to intrinsic and extrinsic regulatory mechanisms.

IV. Blood Flow to the Heart and Skeletal Muscles

Concept: Blood flow to the heart and skeletal muscles is regulated by both extrinsic and intrinsic mechanisms. These mechanisms provide increased rates of blood flow when metabolic requirements of these tissues are raised during exercise.

V. Blood Flow to the Brain and Skin

Concept: Intrinsic control mechanisms help to maintain a relatively constant blood flow to the brain. Blood flow to the skin, by contrast, can vary tremendously in response to regulation by sympathetic nerve stimulation.

VI. Blood Pressure

Concept: The pressure of the arterial blood is regulated by the blood volume, the total peripheral resistance, and the cardiac rate. Regulatory mechanisms adjust these factors in a negative feedback manner to compensate for deviations. Arterial pressure rises and falls as the heart goes through systole and diastole.

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