The amount of urine produced is primarily regulated by the kidneys through processes of filtration, reabsorption, and secretion in the nephrons. Hormones, especially antidiuretic hormone (ADH) and aldosterone, play crucial roles in controlling water reabsorption in the kidneys to maintain fluid balance in the body.
Kidney function in urine regulation
Each kidney contains about a million nephrons, which filter blood to remove waste and excess substances. The glomerulus filters water and solutes from the blood into the nephron tubules. Then, reabsorption returns needed water and substances back to the blood, while secretion adds wastes into the tubules to form urine. The amount of urine produced depends on how much water and dissolved substances, such as salts and wastes, remain in the tubules to be excreted.
Hormonal regulation
- Antidiuretic hormone (ADH) , produced by the hypothalamus and released from the posterior pituitary gland, regulates water reabsorption in the collecting ducts of the nephrons. When the body needs to conserve water (e.g., dehydration), ADH levels increase, making kidneys reabsorb more water and reducing urine volume. When hydration is sufficient, ADH levels drop, increasing urine output.
- Aldosterone influences sodium reabsorption, which indirectly affects water retention and urine volume by regulating salt balance.
Other factors affecting urine volume
- Fluid intake, salt consumption, and hydration status directly impact urine production.
- High salt intake leads to more fluid retention initially, but later kidney output of urine rises to excrete excess salt.
- Dehydration triggers ADH release to conserve water, reducing urine volume.
In summary, urine volume is regulated by kidney filtration and tubular processing, tightly controlled by hormones like ADH to maintain the body's water and electrolyte balance according to needs.
