Aldosterone is called a salt retaining hormone.

Aldosterone is a hormone that is produced by the adrenal glands, which are located on top of the kidneys. It is a part of the renin-angiotensin-aldosterone system (RAAS) and plays a crucial role in regulating the balance of salt and water in the body.

Function of Aldosterone:
Aldosterone acts primarily on the distal tubules and collecting ducts of the kidneys. Its main function is to increase the reabsorption of sodium ions (Na+) from the filtrate in the nephrons back into the bloodstream. This leads to increased water reabsorption and the excretion of potassium ions (K+) and hydrogen ions (H+). By increasing sodium reabsorption, aldosterone helps to maintain the body's electrolyte balance and blood pressure.

Regulation of Aldosterone:
Aldosterone secretion is regulated by several factors, including:
1. Renin: Renin is an enzyme released by the kidneys in response to low blood pressure or low sodium levels. It converts angiotensinogen, a protein produced by the liver, into angiotensin I.
2. Angiotensin II: Angiotensin I is further converted into angiotensin II by an enzyme called angiotensin-converting enzyme (ACE). Angiotensin II acts as a vasoconstrictor and stimulates the release of aldosterone from the adrenal glands.
3. Potassium levels: High levels of potassium in the blood stimulate the release of aldosterone, which helps to excrete excess potassium and maintain normal levels.

Effects of Aldosterone:
The primary effect of aldosterone is to increase sodium reabsorption and water retention. This helps to increase blood volume and maintain blood pressure. It also leads to increased excretion of potassium and hydrogen ions, which helps to regulate their levels in the body.

Aldosterone also has other effects on various organs and tissues in the body, including:
- Sweat glands: It promotes sodium reabsorption in the sweat glands, which reduces sodium loss through sweating.
- Salivary glands: It increases sodium reabsorption in the salivary glands, which helps to maintain electrolyte balance in saliva.
- Colon: It enhances the reabsorption of sodium and water in the colon, leading to the formation of concentrated feces.

In conclusion, aldosterone is called a salt retaining hormone because it increases the reabsorption of sodium ions from the filtrate in the kidneys, helping to maintain the body's electrolyte balance and blood pressure.