In a patient with severe central diabetes insipidus caused by a lack of anti­diuretic hormone secretion, which part of  the  tubule  would  have  the  lowest tubular fluid osmolarity?
In the absence of ADH, the late distal tubule and CD are not permeable to water. Therefore, the  tubular ﬂuid, which is already dilute when it leaves the loop of Henle (about 100 mOsm/L), becomes  further diluted as it ﬂows through the late distal tubule and CD as electrolytes are reabsorbed.
Therefore, the ﬁnal urine osmolarity in the complete absence of ADH is less than 100  mOsm/L.
B
C
D
E