[16.7] the role of hormones in osmoregulation Flashcards
how is homeostatic control of osmoregulation in the blood achieved?
by a hormone that acts on the DCT and collecting duct
what might cause blood to have a lower water potential?
- too little water being consumed
- a lot of sweating
- large amounts of ions eg. NaCl, being taken in
how is lower water potential detected?
- detected by osmoreceptors in the hypothalamus
- when ψ of blood is too low, water is lost from osmoreceptor cells my osmosis so they shrink
- this causes the hypothalamus to produce ADH
where does ADH go once it is produced?
- passes into pituitary gland
- secreted from PG into capillaries
- passes in blood to kidney
what does ADH do?
- increases the permeability to water of the cell-surface membrane of the cells that make up the walls of the DCT and collecting duct
- increases the permeability of the CD to urea, which passes out, thus further lowering the ψ of the fluid around the duct
what happens when specific protein receptors in the cell-surface membrane of DCT and CD cells bind to ADH molecules?
- enzyme phosphorylase is activated
- activation of phosphorylase causes vesicles in the cell to move to and fuse with its cell-surface membrane
what is in the vesicles actived by phosphorylase?
- pieces of plasma membrane that have many water channel proteins (aquaporins)
- when they fuse with the membrane, there are more water channels in the membrane, so the CSM is more permeable to water
is the water potential of the blood increased by ADH?
- no, it is only prevented from getting lower
- reabsorbed water came from the blood in the first place
where will osmoreceptors send nerve impluses to?
- thirst centre of the brain
- this encourages the individual to seek out and drink more water
what happens once the water potential of blood goes back to ‘normal’?
- osmoreceptors in the hypothalamus detect the rise in ψ
- fewer impulses are sent to the pituitary gland
- less ADH is released
- permeability of CDs to water and urea reverts to its former state
what might cause blood to have a higher water potential?
- large volumes of water being consumed
- salts used in metabolism
- salts excreted not being replaced in the diet
summary of the role of hormones in osmoregulation (8)
- osmoreceptors in hypothalamus detect change in water potential
- frequency of nerve impulses to pituitary gland changes
- more / less ADH is released
- more / less ADH, via the blood, leads to an increase / decrease in the permeability of the collecting ducts to water and urea
- more / less water is reabsorbed into the blood from the collecting duct
- more / less dilute urine is produced
- ψ of blood rises / falls
- when ψ of blood is back to normal, osmoreceptors in the hypothalamus cause the PG to release ADH at normal levels
does ADH cause the release of more or less concentrated urine?
- more water is reabsorbed into the blood
- diuresis = production of large volumes of dilute urine
- antidiuresis = production of small volumes of concentrated urine
