Regulation of the cardiovascular system

NIRAJ NIJHAWAN, DAVID C WARLTIER

Regulation of the cardiovascular system has two major homoeostatic goals: to maintain arterial pressure relatively constant and to provide sufficient perfusion to tissues to meet regional metabolic demands. When the requirements of an entire organism for blood flow are altered, the compensatory cardiovascular response involves changing the arterial perfusion pressure. On the other hand, when the perfusion to a particular organ system is altered, cardiovascular compensation occurs by adjusting the calibre of specific blood vessels. The most important variable that is controlled in the regulation of the circulation is arterial blood pressure. Arterial pressure has often been related to Ohm's law in physics. This implies that blood pressure (analogous to voltage) is directly proportional to the product of cardiac output (current) and peripheral vascular resistance (resistance). Neural and humoral control of arterial pressure are mediated through alterations of both cardiac output and/or peripheral resistance.

The physical characteristics of the vascular system are dynamic and more complex than previously realised. Age and certain pathophysiological conditions, such as hypertension, diabetes, and atherosclerosis, result in a progressive stiffening of the conduit (large artery) vessels related to intimal and smooth muscle changes. Vascular smooth muscle hypertrophy as a primary or a secondary phenomenon results in a hypersensitivity to control mechanisms. In any discussion pertaining to cardiovascular regulatory mechanisms, pathophysiological changes must be considered. Interestingly, ventricular hypertrophy may proceed with elevated or normal blood pressure. This appears to be related to the very important pulsatile component of ventricular load, which is not necessarily captured by measurements of blood pressure.1 An understanding of the differential impact of conduit and resistance vessels will expand future investigations into cardiovascular control mechanisms as well as pharmocotherapy.

Acute mechanisms for regulation of arterial pressure are coordinated in the cardiovascular control centres of the brain stem. These centres regulate both cardiac output and peripheral resistance and, therefore, are able to exert powerful control of arterial pressure. The brain stem cardiovascular centres are in turn influenced by impulses from other neural centres, as well as by numerous sensors within and external to the circulation.

Further regulation of the circulation is mediated by endogenous chemical substances, which are released into the circulation and have a direct effect on the heart and/or vasculature in both physiological and pathophysiological states. Many tissues have the ability to regulate blood flow by local mechanisms, preferentially altering regional perfusion without changes in cardiac output and systemic vascular resistance. Finally, the kidneys are the long term regulators of the entire circulation by manipulating the overall fluid status of an organism. This chapter addresses these different mechanisms individually, but ultimately all are closely integrated and function in unison to regulate the circulation.

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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