Question

ADH acts on
(a)Loop of Henle
(b)Collecting tubule
(c)Vasa efferentia
(d)Vasa deferentia

Answer 1

Hint: Antidiuretic hormone (ADH), also known as vasopressin, is a small peptide hormone that regulates the body’s retention of water. The ADH mainly functions in the kidney is to regulate the volume and osmolarity of the urine.

Complete answer:
This hormone synthesizes in the supraoptic and paraventricular nuclei in the hypothalamus. After that this synthesized ADH is transported to the posterior pituitary gland via the neurohypophysial capillaries. In the posterior pituitary gland, its synthesis is completed and it is stored here until it is ready to be secreted into the circulation.
When changes in blood volume, body fluid volume, and ionic concentration occurs, osmoreceptors in the body get activated. These receptors get activated when the body loses excessive fluid, which stimulates the hypothalamus to release antidiuretic hormone (ADH) or vasopressin from the neurohypophysis. ADH facilitates water reabsorption from the latter parts of the tubule (Distal convoluted tubule and collecting duct), thereby preventing diuresis. When body fluid volume increases, it can switch off the osmoreceptors and suppress the ADH release to complete the feedback. ADH mainly acts on collecting ducts of the kidney and increases the water reabsorption in this part.

Additional Information: 1) The hormone ADH acts through a G-protein coupled receptor to increase the transcription and insertion of Aquaporin–2 channels to the apical membrane of the DCT and CD cells.
2) In high concentrations, ADH can also act on the blood vessels to increase peripheral vascular resistance, the result of which is increased blood pressure. During hypovolemic shock, this mechanism is useful in restoring blood pressure.
3) Syndrome of inappropriate ADH (SIADH) secretion is characterized by hyponatremia secondary to excessive retention of free water. The symptoms that can be seen are mild, but in severe cases, cerebral edema and resultant neurological dysfunction can occur.
4) A very similar substance, lysine vasopressin (LVP) or lypressin, has the same function in pigs and its synthetic version was used in human arginine vasopressin(AVP) deficiency, although it has been largely replaced by desmopressin.
So, the correct answer is, ‘collecting tubules.’

Note: ADH has also served as a medication to treat two important bleeding disorders aside from its role in homeostasis and its part in a variety of pathologies. They are von Willebrand disease and hemophilia A. Mutations that lead to disruption of the synthesis or function of the von Willebrand factor (VWF), finally causes Von Willebrand disease, which is the most common inherited bleeding disorder. And the second disorder is hemophilia A, which is a bleeding disorder owed to either an acquired or inherited lack of factor VIII. The desmopressin also stated that it promotes the release of factor VIII from the endothelium, thus bridging the missing gap in hemophilia A's coagulopathy.