What is inserted into the plasma membranes of the cells that make up the wall of the collecting duct when ADH binds the receptors on their surface?

When ADH (Antidiuretic Hormone) binds to the receptors on the surface of the cells that make up the wall of the collecting duct, Aquaporin-2 water channels are inserted into the plasma membranes of these cells.

Here are the steps:

1. ADH is released from the posterior pituitary gland into the bloodstream.
2. ADH travels in the blood to the kidneys.
3. In the kidneys, ADH binds to receptors on the cells of the collecting duct.
4. This binding triggers a signal transduction pathway within the cells.
5. As a result of this pathway, vesicles containing Aquaporin-2 water channels are moved to and fuse with the plasma membrane.
6. The Aquaporin-2 channels are inserted into the plasma membrane, increasing the membrane's permeability to water.
7. This allows water to be reabsorbed from the urine in the collecting duct back into the bloodstream, concentrating the urine.