The Role Of Hormones In Osmoregulation Flashcards
How does the body respond to fall in water potential.
1) Cells called osmoreceptors in the hypothalamus of the brain detect fall in water potential.
2) When the water potential of the blood is low water is lost from these osmoreceptors bis osmosis.
3) As a result of this water loss the osmoreceptors shrink which causes the hypothalamus to produce the hormone called an antidiuretic hormone (ADH).
4) ADH passes to the posterior pituitary gland from where it is secreted into the capillaries.
5) ADH passes in the blood to the kidneys where it increases the permeability of the cell membranes (of the cells that make up the walls of the distal convoluted tube and the collecting duct) to water.
6) Specific protein receptors on cell surface membrane of these cells bind to ADH molecules, this leads to activation of the enzyme phosphorylase within the cell.
7) The activation of phosphorylase causes vesicles in the cell to fuse to the cell membrane.
8) The vesicles contain pieces of plasma membrane which have numerous aquaporins and so when they fuse to membrane the number of water channels increased which increases the permeability to water.
9) ADH increases the permeability of the collecting duct to urea which passes out and lowers further the water potential of the fluid around the duct.
10) Therefore the combined effect is that more water leaves collecting duct via osmosis down a water potential gradient, entering the blood.
11) As the water originally came from the blood this will not therefore increase its water potential but will prevent it from decreasing further, osmoreceptors send nerve impulses to the thirst centre of brain which encourages the individual to drink more water.
12) Osmoreceptors in hypothalamus detect rise in water and send fewer impulses to pituitary gland. This reduces release of ADH and the permeability of the collecting ducts to water and reverts to its previous state.
What would lower the water potential of the blood.
This is caused by a rise in solute which may be caused by:
1) too little water being consumed
2) lots of sweating occurring
3) large amounts of ions being taken in
Why would the water potential of the blood rise.
This occurs when the volume of solute decreases. This may be caused by:
1) large volumes of water being consumed
2) salts used In metabolism or excreted not being replaced in the diet
How does the body respond to a rise in water potential in the blood.
1) osmoreceptors in the hypothalamus detect the rise in water potential and increase the frequency of nerve impulses to the pituitary gland to rescue its release of ADH.
2) Less ADH via the blood leads to a decrease in the permeability of the collecting ducts to water and urea.
3) Less water is reabsorbed into the blood from the collecting duct.
4) More dilute urine is produced and the water potential of the blood falls.
5) When the water potential of the blood has returned to normal, the osmoreceptors in the hypothalamus cause the pituitary gland to raise its ADH release black to normal levels.
Describe the second messenger model.
This involves the hormones adrenalin and glucagon and helps control blood glucose levels.
1) Adrenaline binds to a trans-membrane protein receptor within the cell-surface membrane of a liver cell.
2) The binding of adrenaline causes the protein to change shape on the inside of the membrane.
3) This change of protein shape leads to the activation of an enzyme called adenyl cyclase. The activated adenyl cyclase converts ATP to cyclic AMP (cAMP).
The cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape therefore activating it.
4) The active protein kinase enzyme catalyses the conversion of glycogen to glucose which moves out of the liver cells by facilitated diffusion and into the blood through channel proteins.
What is glycogenesis?
The conversion of glucose into glycogen.
What is glycogenolysis?
The breakdown of glycogen to glucose.
What is gluconeogenesis?
The production of glucose from sources other than carbohydrates e.g. glycerol and amino acids.
