Mechanism of Action of Vasopressin || How Antidiuretic Hormone Increases Water Reabsorption

Summary

This video explains how vasopressin (antidiuretic hormone) regulates water reabsorption in the kidney, specifically in the collecting duct. It details the role of aquaporins, particularly aquaporin 2 (AQP2), which is regulated by vasopressin through its V2 receptor. In the presence of vasopressin, AQP2 is inserted into the apical membrane, enhancing water reabsorption from the lumen into the interstitium. This process is reversed when vasopressin levels decrease, regulating the balance of water in the body. The video simplifies this mechanism, making complex medical concepts easy to understand, akin to watching a cartoon.

Takeaways

• 😀 Vasopressin (antidiuretic hormone) increases water reabsorption in the kidneys.
• 😀 The collecting duct in the kidney is the primary site for this action.
• 😀 The interstitium is hyperosmolar, meaning it has a low water concentration compared to the lumen.
• 😀 Water reabsorption occurs through aquaporin 2 on the apical membrane and aquaporin 3 and 4 on the basolateral membrane.
• 😀 Aquaporin 3 and 4 are always present on the basolateral membrane, facilitating water transport into the cell.
• 😀 Aquaporin 2 is the limiting factor in water reabsorption, and its presence on the apical membrane is regulated by vasopressin.
• 😀 In the absence of vasopressin, minimal aquaporins are present on the apical membrane, limiting water reabsorption.
• 😀 Vasopressin binds to V2 receptors on the basolateral membrane, activating the cAMP pathway and causing exocytosis of vesicles.
• 😀 Exocytosis results in the insertion of aquaporin 2 into the apical membrane, increasing water reabsorption.
• 😀 Increased water entry at the apical membrane leads to increased water exit at the basolateral membrane, boosting reabsorption.
• 😀 Once water reabsorption is sufficient, vasopressin levels decrease, and aquaporins are withdrawn from the apical membrane to reduce water reabsorption.

Q & A

What is the main function of vasopressin in the collecting duct?

Vasopressin, also known as antidiuretic hormone, increases water reabsorption in the collecting duct by facilitating the insertion of aquaporin 2 channels into the apical membrane of epithelial cells.

Where in the kidney does vasopressin exert its effect?

Vasopressin acts on the collecting duct in the kidney, which is where water reabsorption is regulated.

What is the role of aquaporins in water reabsorption?

Aquaporins are water channels that allow the movement of water across cell membranes. Aquaporin 2 is located on the apical membrane, while aquaporins 3 and 4 are found on the basolateral membrane, facilitating water transport from the cell to the interstitium.

How does the osmotic gradient influence water reabsorption?

The osmotic gradient, with a lower water concentration in the interstitium compared to the lumen of the collecting duct, drives water from the lumen into the interstitium, promoting water reabsorption.

What is the limiting factor for water reabsorption in the collecting duct?

The limiting factor for water reabsorption is the quantity of aquaporin 2 on the apical membrane. In the absence of vasopressin, there are minimal aquaporin 2 channels on the apical membrane.

How does vasopressin increase the expression of aquaporin 2?

Vasopressin binds to the V2 receptor on the basolateral membrane, activating the cAMP pathway. This leads to the exocytosis of vesicles containing aquaporin 2, which are then inserted into the apical membrane, increasing water reabsorption.

What happens to aquaporins after vasopressin levels decrease?

When vasopressin levels decrease, aquaporins 2 are removed from the apical membrane and stored inside the cell, leading to reduced water reabsorption.

What is the role of aquaporins 3 and 4 in water reabsorption?

Aquaporins 3 and 4 are always present on the basolateral membrane of epithelial cells in the collecting duct, allowing water to exit the cell and enter the interstitium once it is transported through the apical membrane.

How does the Gs-coupled receptor contribute to the action of vasopressin?

The V2 receptor for vasopressin is a Gs-coupled receptor. Upon activation, it stimulates the cAMP pathway, which triggers the exocytosis of vesicles containing aquaporin 2 to the apical membrane.

How is the process of water reabsorption regulated in response to the body’s needs?

Water reabsorption is regulated by vasopressin levels. When the body needs more water, vasopressin levels rise, increasing aquaporin 2 expression and water reabsorption. When sufficient water is reabsorbed, vasopressin levels decrease, reducing the reabsorption rate.