In chronic coronary heart disease, a condition of congestive heart failure may develop over time. The progressively weakened heart muscle or myocardium is unable to maintain an adequate cardiac output to sustain normal blood circulation. This leads to fluid imbalances and edema, especially pulmonary edema. The edema puts further stress on the weakened heart.
Two hormonal mechanisms are involved in fluid balance and both contribute to cardiac edema. These are -
Rennin angiotensin aldosterone mechanism: As the heart fails to pump the blood forward, there is a reduction in the renal blood flow. This triggers the rennin- angiotensin system. Rennin, is produced in the renal cortex, and when released it combines with its substrate angiotensinogen produced by the liver. Angiotensin I and II are formed. Angiotensin II stimulates the adrenal gland to produce aldosterone.
Aldosterone causes a reabsorption of the sodium ion and water in the distal tubules of the kidney. In congestive heart failure, this further increases the fluid in the body. ADH also stimulates more water resorption from the distal tubules and increases water retention in the body. In congestive heart failure these abnormal events produce a serious dislocation in the body’s water compartments.