Assume that fluid enters the distal convoluted tubule with an osmolarity of 100 mOsm and that the maximum osmolarity of medullary interstitial fluid is 1100 mOsm. As plasma ADH levels rise, the osmolarity of the urine
a) approaches 300 mOsm, the normal osmolarity of plasma
b) approaches 1100 mOsm as an upper limit
c) eventually exceeds 1100 mOsm
d) approaches 100 m0sm as a lower limit
study guide question thank you
a
To determine the answer, we need to understand the role of ADH (antidiuretic hormone) in the distal convoluted tubule and urine osmolarity regulation.
ADH is released by the pituitary gland in response to increased osmolarity (concentration) of the blood. It acts on the distal convoluted tubule, making it more permeable to water. As a result, more water is reabsorbed from the tubule back into the bloodstream, which helps to reduce the concentration of solutes in the urine.
In this scenario, we have fluid entering the distal convoluted tubule with an osmolarity of 100 mOsm. The maximum osmolarity of the medullary interstitial fluid, which surrounds the tubule, is 1100 mOsm.
As plasma ADH levels rise, more water will be reabsorbed from the distal convoluted tubule, resulting in less water being excreted in the urine. This will cause the concentration of solutes in the urine to increase, approaching the maximum osmolarity of the interstitial fluid (1100 mOsm).
Therefore, the correct answer is (b) the osmolarity of the urine approaches 1100 mOsm as an upper limit.