The filtrate moves into the nephron loop that dips into and then out of the center, or medulla, of the kidney. The nephron loop helps to concentrate urine. In the distal convoluted tubule, more reabsorption and secretion occur. The posterior pituitary gland secretes ADH in response to signals from the hypothalamus, which senses the osmotic pressure of blood. ADH increases permeability of the distal convoluted tubule and the collecting duct so more water is reabsorbed and urine is concentrated.
Aldosterone increases the kidneys' salt retention.
The adrenal glands release aldosterone in response to either low sodium concentration in the plasma or low blood pressure. Problems in the urinary system include nighttime bedwetting, urinary tract infections, kidney stones, and kidney failure. If the kidneys fail, a kidney transplant or dialysis becomes necessary. The McGraw-Hill Companies. Any use is subject to the Terms of Use and Privacy Policy .