Changes

Angiotensin II is a potent vasoconstrictor (causing an increase in mean arterial pressure), which also causes the direct stimulation of sodium retention in the proximal convoluted tubule of the kidney, via its increased synthesis and release of aldosterone. Aldosterone stimulates reabsorption of sodium and chloride, and secretion of potassium and protons. Initially, effects are advantageous by protecting perfusion to essential vascular beds and expanding the circulation fluid volume, and therefore increasing contractility by the Starling mechanism. Disadvantages include increased systemic vascular resistance, therefore increased myocardial work and increased myocardial oxygen demand. Expanded circulation fluid volume ultimately results in congestion of vascular beds when the Starling mechanism is not effective in the failing heart. Angiotensin II and aldosterone have effects at the level of the gene involving altered expression, which may lead to a progression of the myocardial dysfunction present. They therefore play a role in the regulation of hypertrophy and fibrosis.

Angiotensin II is a potent vasoconstrictor (causing an increase in mean arterial pressure), which also causes the direct stimulation of sodium retention in the proximal convoluted tubule of the kidney, via its increased synthesis and release of aldosterone. Aldosterone stimulates reabsorption of sodium and chloride, and secretion of potassium and protons. Initially, effects are advantageous by protecting perfusion to essential vascular beds and expanding the circulation fluid volume, and therefore increasing contractility by the Starling mechanism. Disadvantages include increased systemic vascular resistance, therefore increased myocardial work and increased myocardial oxygen demand. Expanded circulation fluid volume ultimately results in congestion of vascular beds when the Starling mechanism is not effective in the failing heart. Angiotensin II and aldosterone have effects at the level of the gene involving altered expression, which may lead to a progression of the myocardial dysfunction present. They therefore play a role in the regulation of hypertrophy and fibrosis.

===Kidney and Fluid Balance Mechanisms===

==Kidney and Fluid Balance Mechanisms==

The kidneys help to regulate the blood pressure by increasing (when blood pressure falls) or decreasing (when blood pressure rises) the blood volume, and also by the renin-angiotensin system described above. The kidney-fluid system is the main method of the long-term control of blood pressure.

The kidneys help to regulate the blood pressure by increasing (when blood pressure falls) or decreasing (when blood pressure rises) the blood volume, and also by the renin-angiotensin system described above. The kidney-fluid system is the main method of the long-term control of blood pressure.