Osmoregulation

Question 1

The amount of water lost in the urine is controlled by…

Answer 1

…by the ADH in a negative feedback system

Question 2

Where is ADH produced and secreted into?

Answer 2

The hypothalamus and posterior pituitary gland

Question 3

What does ADH do?

Answer 3

Increases the permeability of the distal convoluted tubule and the collecting duct.

Question 4

The mechanism of ADH

Answer 4

-ADH released from pituitary gland and carried in blood to cells of collecting duct
-Hormone binds to receptors on the cell membrane and triggers the formation of cyclic AMP (second messenger)
-Vesicles in cells lining of collecting duct fuse with the cell surface membranes on the side of the cell in contact with the tissue fluid of medulla.
-The vesicle membranes have aquaporins which when inserted into cell surface membrane, make it permeable to water.
-This provides route for water to move out of tubule cells into tissue fluid of medulla and blood capillaries by osmosis.

Question 5

The more ADH released…

Answer 5

…the more water channels are inserted into membranes of tubule cells and so easier for more water to leave tubules by diffusion=very concentrated urine
=water returned to capillaries, water potential of blood and tissue fluid maintained

Question 6

ADH levels fall…

Answer 6

…levels of cAMP fall, water channels removed from tubule cell membranes and enclosed vesicles
-collecting duct becomes impermeable to water once more, so no water can leave
=large amounts of very dilute urine
=maintains water potential of blood and tissue fluid

Question 7

Osmoreceptors

Answer 7

In hypothalamus
-sensitive to concentration of inorganic ions in the blood and are linked to release of ADH