Question

If kidneys fail to reabsorb water, the effect on tissues would be-
A. Remains unaffected
B. Shrink and shrivel
C. Absorb water from blood plasma
D. Take more oxygen from the blood

Answer 1

The reabsorption of water i.e., the movement of water and solutes from the tubules back to the plasma occurs in the kidney under the effect of vasopressin hormone. This majorly occurs in the Proximal convoluted tubule and the water is returned back to the circulation in the plasma.

Complete answer:
Kidneys are a pair of bean-shaped organs in the renal system that filter the blood in the body, maintain the fluid/water balance, and help in the passing of waste from the body in the form of urine. The reabsorption of water in kidneys occurs passively through osmotic gradients with the help of water channels. This gradient is formed as a result of the active movement of sodium chloride out of the tubular fluid. Water moves passively outside the tubular fluid to compensate for the gradient produced. This reabsorption of water is the reason why we produce concentrated urine.

About 99% of the water is reabsorbed in this process and released back into the circulation. The urine eliminated is 1% of the fluid filtered.
If the kidneys fail to reabsorb water, useful minerals and water will be eliminated from the body in the form of urine, resulting in dilute urine. The body will become dehydrated and the tissues in the body will shrink and shrivel due to the presence of an osmotic gradient created by the movement of sodium chloride outside the tubular fluid. The sodium level in the body can increase rapidly.

Option B: The tissues in the body will shrink and shrivel due to the dehydration caused in the body. Therefore, this is the correct option.
All the other options are irrelevant.

Hence, the correct answer is option (B)

Note: The reabsorption of water in the kidneys is due to the effect of Anti Diuretic Hormone or Vasopressin hormone produced by the hypothalamus and stored in the pituitary gland. This hormone creates water channels or aquaporins in the membrane of kidney tubules. When the osmolarity is increased in the blood, ADH is released and the water is reabsorbed from the tubular cells to plasma, decreasing the plasma osmolarity.