Final answer:
Sodium retention in response to decreased cardiac output leads to increased blood pressure, due to the body's regulatory mechanisms aiming to restore blood volume and pressure. Aldosterone plays a crucial role in this process by promoting the reabsorption of sodium and water, ultimately affecting blood pressure and urine output.
Step-by-step explanation:
Sodium retention is a response to decreased cardiac output, which ultimately results in increased blood pressure. When the cardiac output drops, the kidneys respond by releasing the enzyme renin, which leads to the production of angiotensin, a potent vasoconstrictor. This cascade also triggers the release of aldosterone from the adrenal glands, which works on the kidneys to promote reabsorption of sodium. The absorption of sodium also encourages water retention in order to increase blood volume and thus increase blood pressure.
In addition, aldosterone facilitates the excretion of potassium, which could potentially lead to hypokalemia. The retention of sodium and water by the kidneys consequently decreases urine output, contrary to increasing it. Thereby, the body's response to decreased cardiac output aims to restore normal blood pressure and maintain homeostasis.