How does angiotensin-II help to restore fluid balance when a person is dehydrated?

Verified step by step guidance

1. Understand that dehydration leads to a decrease in blood volume and blood pressure, which triggers the renin-angiotensin-aldosterone system (RAAS) to restore fluid balance.
2. Recognize that angiotensin-II is a key hormone in the RAAS pathway, produced when renin (from the kidneys) converts angiotensinogen (from the liver) into angiotensin-I, which is then converted to angiotensin-II by the enzyme angiotensin-converting enzyme (ACE) in the lungs.
3. Explain that angiotensin-II acts as a potent vasoconstrictor, narrowing blood vessels to increase blood pressure and improve circulation despite reduced fluid levels.
4. Describe how angiotensin-II stimulates the release of aldosterone from the adrenal glands, which promotes sodium reabsorption in the kidneys. Sodium reabsorption increases water retention, helping to restore blood volume.
5. Highlight that angiotensin-II also stimulates the release of antidiuretic hormone (ADH) from the posterior pituitary gland, which increases water reabsorption in the kidneys, further aiding in fluid balance restoration.

Key Concepts

Angiotensin-II

Angiotensin-II is a peptide hormone that plays a crucial role in the body's fluid balance and blood pressure regulation. It is produced from angiotensinogen in response to low blood pressure or low blood volume. Angiotensin-II acts primarily by constricting blood vessels, which increases blood pressure, and stimulating the release of aldosterone, promoting sodium and water reabsorption in the kidneys.

Fluid Balance

Fluid balance refers to the equilibrium between the intake and output of fluids in the body, essential for maintaining homeostasis. When a person is dehydrated, the body loses more water than it takes in, leading to a decrease in blood volume and pressure. Restoring fluid balance involves mechanisms that increase water retention and promote fluid intake, ensuring that vital organs function properly.

Aldosterone

Aldosterone is a steroid hormone produced by the adrenal glands that regulates sodium and potassium levels in the body. In response to angiotensin-II, aldosterone promotes the reabsorption of sodium in the kidneys, which in turn leads to water retention. This process helps to increase blood volume and restore fluid balance, particularly during states of dehydration.