What physiological responses occur when extracellular fluid (ECF) volume increases?

A. Aldosterone production increases, promoting sodium retention: Aldosterone is secreted in response to low ECF volume or hypotension to conserve sodium and water. In a volume-expanded state, aldosterone secretion is inhibited. This allows the kidneys to excrete excess sodium and reduce the total fluid volume.

B. ADH secretion is stimulated, increasing water retention: Antidiuretic hormone is suppressed when ECF volume is high to facilitate the excretion of dilute urine. Stimulation of ADH would cause further water retention, worsening the volume overload. The body aims to reduce water reabsorption in the collecting ducts.

C. Natriuretic peptides are released, promoting sodium and water excretion: Atrial natriuretic peptide is secreted by cardiomyocytes in response to increased stretch from high volume. It inhibits renin and aldosterone while increasing the glomerular filtration rate. This promotes the loss of sodium and water to lower blood pressure.

D. Thirst is increased, leading to more fluid intake: High ECF volume suppresses the thirst mechanism to prevent further intake. Increasing thirst would be counterproductive and potentially dangerous in a volume-overloaded patient. The hypothalamus responds to high volume by decreasing the drive to drink.