(30) GTAC - Chemical Signalling: Antidiuretic hormone (ADH)

Dehydration Process in the Body

Detection of Dehydration

• Water levels in the blood decrease, triggering a response.

• Receptors in the hypothalamus detect the reduction in blood water levels.

• These receptors are known as osmoreceptors.

Role of Antidiuretic Hormone (ADH)

• In response to dehydration, osmoreceptors in the hypothalamus secrete ADH.

• ADH is a hydrophilic peptide hormone.

• It is released from the pituitary gland into the bloodstream.

ADH in the Kidneys

• ADH acts on the kidneys, where urine production occurs.

• Nephrons in the kidneys filter blood, removing urea, salts, and other solutes.

Collecting Duct Function

• The collecting duct of the nephron is crucial for water reabsorption.

• ADH receptors are located on the cells lining the collecting duct.

Mechanism of Action

• When ADH binds to its receptors, it triggers a signal transduction process.

• This process involves a cascade of molecular interactions inside the cells.

• It activates vesicles containing water channels called aquaporins.

• Aquaporins are inserted into the plasma membrane of the collecting duct cells.

Effects of ADH on Urine Production

• The insertion of aquaporins into the membrane increases water permeability.

• More water is reabsorbed from the collecting duct back into the bloodstream.

• As a result, less water is excreted in urine.

• Urine becomes more concentrated due to reduced water loss.

Summary of ADH Function

• ADH conserves water when the body is dehydrated.

• It decreases urine production, helping to maintain hydration levels.