How would a diuretic affect water reabsorption into the blood?

Answer 1

A diuretic is a substance that tends to cause diuresis (increased urine flow) by hindering the amount of water reabsorbed back into the blood. the mechanism of how this occurs depends on the type of diuretic. for example some diuretics impede the body's ability to reabsorb Na at the ascending loop of Henle thus not increasing the osmolarity of the extracellular fluid which would in turn cause water reabsorption, so the water remains in the lumen of the nephron and is excreted causing increased urine volume. other diuretics may act on the proximal and distal convoluted tubules causing water retension due to decreased Nacl reabsorption or Na reabsorption or even potassium.

Due to the fact that a diuretic will cause water to lost in the urine, this will cause an increase in osmolarity above the setpoint of 300mOsm/L, therefore more ADH (anti-diuretic hormone) is released into the bloodstream. When ADH reaches the kidney, its main targets are the distal tubules and the collecting ducts. The ADH brings about changes that make the epithelium more permeable to water. the resulting increase in water reabsorption concentrates the urine, reducing urine volume and lowers blood osmolarity back to set point.