Correct Option
The correct option is ADH.
Explanation
The regulation of urine concentration and volume is primarily controlled by hormonal feedback mechanisms involving the hypothalamus, pituitary gland, and the heart. These hormones adjust the permeability of the nephron tubules to water and electrolytes to maintain body fluid osmolarity.
Option Analysis
- ADH ADH (Correct): Antidiuretic Hormone (ADH), also known as Vasopressin, is synthesized by the hypothalamus and released from the neurohypophysis (posterior pituitary). It acts on the distal convoluted tubule (DCT) and the collecting duct of the nephron. ADH increases the permeability of these segments to water (by inserting aquaporin channels), facilitating water reabsorption into the interstitium. This process prevents excessive water loss in urine (diuresis).
- Aldosterone Aldosterone (Incorrect): Aldosterone is a mineralocorticoid secreted by the adrenal cortex. It acts mainly on the DCT and collecting duct to stimulate the reabsorption of Sodium (Na+) and the excretion of Potassium (K+). While water follows sodium osmotically, the primary function of aldosterone is electrolyte balance and blood pressure regulation via the RAAS mechanism, rather than direct water channel regulation like ADH.
- ANF ANF (Incorrect): Atrial Natriuretic Factor (ANF) is produced by the atrial wall of the heart in response to increased blood volume and pressure. It promotes the excretion of Sodium (natriuresis) and water, thereby lowering blood pressure. It acts as an antagonist to the Renin-Angiotensin-Aldosterone System (RAAS).
- Thyroxine Thyroxine (Incorrect): Thyroxine is a thyroid hormone responsible for regulating the Basal Metabolic Rate (BMR) and metabolism of carbohydrates, proteins, and fats. It does not play a direct role in the acute regulation of water reabsorption in the kidney.
Key Takeaway
ADH (Vasopressin) is the primary hormone responsible for facultative water reabsorption in the distal parts of the nephron, directly preventing diuresis by increasing tubular permeability to water.