Question

Using approximately 200 words, Explain the role of antidiuretic hormone (vasopressin) in controlling extracellular fluid osmolarity and its affect on urine volume and concentration.

Answer 1

Every day 180 L of glomerular filtrate is formed with large quantity of water. So the concentration of urine is very essential.

Cortical interstitial fluid is isotonic to plasma with the osmolarity of 300 mOsm/L. Osmolarity of medullary interstitial fluid near the cortex is also 300 mOsm/L. However, while proceeding from outer part towards the inner part of medulla, the osmolarity increases gradually and reaches the maximum at the inner most part of medulla near renal sinus. Here, the interstitial fluid is hypertonic with osmolarity of 1,200 mOsm/L

FORMATION OF CONCENTRATED URINE; involve two process

1. countercurrent system
2. Secretion of ADH.

Reabsorption of water from distal convoluted tubule and collecting duct – facultative water reabsorption by ADH
it is the type of water reabsorption in distal convoluted tubule and collecting duct that occurs by the activity of antidiuretic hormone (ADH).
Normally, the distal convoluted tubule and the collecting duct are not permeable to water. But in the presence of ADH, they become permeable to water, so it is reabsorbed.

A large quantity of water is removed from the fluid while passing through distal convoluted tubule and
collecting duct. So, the urine becomes hypertonic with an osmolarity of 1,200 mOsm/L