Actions of ADH and aldosterone Indicate whether the following statements regardi

Question

Actions of ADH and aldosterone Indicate whether the following statements regarding the actions of ADH and aldosterone are true or false.

1. Aldosterone acts on the distal tubule and the upper part of the collecting duct.

2. Aldosterone stimulates the active transport of two molecules of Na+ for every three molecules of K+ .

3. If Na+ concentrations in the blood decrease below normal levels, aldosterone will be secreted.

4. ADH is secreted when the body’s stores of water are plentiful.

5. ADH increases the number of water channels present in the membranes of the collecting ducts.

Explanation / Answer

1. Aldosterone acts on the distal tubule and the upper part of the collecting duct, (True)

2. Aldosterone stimulates the active transport of two molecules of Na+ for every three molecules of K+ . FALSE: based on the below given information:

Acting on the nuclear moneralcorticoid receptors (MR) within the principal cells of the distal tubule and the collecting duct of the kidney nephron, it upregulates and activates thebasolateral Na+/K+ pumps, which pumps three sodium ions out of the cell, into the interstitial fluid and two potassium ions into the cell from the interstitial fluid. This creates a concentration gradient which results in reabsorption of sodium (Na+) ions and water (which follows sodium) into the blood, and secreting potassium (K+) ions into the urine (lumen of collecting duct) (Arai, Keiko, 2001).

3. If Na+ concentrations in the blood decrease below normal levels, aldosterone will be secreted. (true) based on the below given information

Aldosterone is part of a group of linked hormones, which form the renin-angiotensin -aldosterone system. Activation of this system occurs when there is decrease in blood flow to the kidneys following loss of blood volume or a drop in blood pressure (eg due to a haemorrhage) or decrease in plasma sodium concentration. Renin is an enzyme that leads to a series of chemical reactions resulting in the production of angiotensin II, which in turn stimulate aldosterone release. Aldosterone causes an increase in salt and water reabsorption into the bloodstream from the kidney thereby increasing the blood volume, restoring salt levels and blood pressure. Once salt levels and blood pressure are corrected and the body becomes rehydrated, the level of renin in the bloodstream falls and therefore the amount of aldosterone in the blood also falls, meaning more water is excreted in the urine. The renin-angiotensin-aldosterone system is an example of a negative feedback system.

The other two main regulators of aldosterone secretion are increase in the plasma potassium concentration and adrenocorticotropic hormone (ACTH) secreted by the anterior pituitary, which can act via either positive or negative feedback mechanisms, depending on the extent of changes in the levels of these two regulators.

4. ADH is secreted when the body’s stores of water are plentiful. (false) As ADH stands for antidiuretic hormone, so when the body’s stores of water are plentiful there is no requirement for secretion of ADH, hence false.

5. ADH increases the number of water channels present in the membranes of the collecting ducts, true a ADH up regulates the level of aquaporins the water channels.

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