Discuss three hormones that regulate sodium ion concentration in the extracellular fluid (ECF)
What will be an ideal response?
The two main hormones that increase sodium ion retention are angiotensin-II and aldosterone. A low extracellular sodium ion concentration is one of the major stimuli that trigger the renin-angiotensin-aldosterone system (RAAS). Angiotensin-II increases the reabsorption of sodium ions from the proximal tubule and stimulates aldosterone secretion, which causes sodium ion reabsorption from the distal tubule. These actions indirectly increase water reabsorption, as water follows sodium ions by osmosis. When secretion of both hormones decreases, the number of sodium ions (as well as the amount of water) reabsorbed decreases. Another hormone that influences sodium ion balance is atrial natriuretic peptide (ANP), which decreases sodium ion (and water) reabsorption. Together, these three hormones maintain a relatively stable plasma sodium ion concentration despite significant changes in intake.
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