Explain How Antidiuretic Hormone Regulates Water Balance in the Body
Antidiuretic hormone (ADH), also known as vasopressin, plays a critical role in maintaining water balance and regulating blood pressure. It is synthesized in the hypothalamus and stored and released by the posterior pituitary gland.
Mechanism of Action
- When the body is dehydrated or blood osmolality increases, osmoreceptors in the hypothalamus are activated.
- ADH is released into the bloodstream and acts on the kidneys, specifically on the collecting ducts of nephrons.
- ADH increases the permeability of the collecting ducts by stimulating the insertion of aquaporin-2 channels in their membranes.
- This allows more water to be reabsorbed back into the blood, concentrating the urine and reducing water loss.
Outcome
- Conservation of body water
- Decrease in urine volume
- Restoration of blood osmolarity and volume
Clinical Relevance
- Deficiency of ADH causes diabetes insipidus, leading to excessive urination and dehydration.
- Excess ADH can cause syndrome of inappropriate antidiuretic hormone secretion (SIADH), leading to water retention and hyponatremia.
In summary, ADH is essential for water homeostasis, acting on the kidneys to prevent dehydration by reducing water loss in urine.