Osmoregulation Flashcards
What is the definition of osmoregulation
-controlling the water potential of the blood, plasma, and tissue fluid, within very narrow boundaries, regardless of external factors
What is the importance of osmoregulation?
-if water enters our cells by osmosis they may burst and die, but if water leaves our cells by osmosis they may shrink and die
What does the hormone ADH stand for?
Anti-diuretic hormone
Where is ADH made and stored?
-it is made in the hypothalamus by special neurosecretory cells called OSMORECEPTORS and is then stored in the posterior pituitary gland
What is the role of osmoreceptors?
-to monitor the water potential of the blood flowing through the brain and if this falls, they tigger the release of more ADH from the posterior pituitary gland
How is ADH released?
-the special neurosecretory cells are different to normal neurones because they make hormones
-when the blood water potential falls, the osmoreceptors in the hypothalamus lose water by osmosis
-this triggers them to send nerve impulses at a faster rate to activate the release of more ADH into the blood from the posterior pituitary gland
What cells does the ADH act on and how does this work?
-the cells lining the collecting duct and the distal convoluted tubule
-it causes more water to be saved back into the blood
-these cells have specific shaped receptors (proteins) which are complementary to the shape of ADH, allowing it to attach
Why does ADH use a second messenger system?
-because it is a protein hormone, and so is too big to pass through the membranes
Explain how blood ADH level rises when you’re dehydrated
-water content of blood drops, so it’s water potential drops
-this is detected by osmoreceptors in the hypothalamus
-the posterior pituitary gland is stimulated to release more ADH into the blood
-more ADH means that the DCT and collecting duct are more permeable, so more water is reabsorbed into the blood by osmosis
-a small volume of high concentrated urine is produced and less water is lost
Explain how blood ADH level falls when you’re hydrated
-water content of the blood rises, so it’s water potential rises
-this is detected by osmoreceptors in the hypothalamus
-the posterior pituitary gland releases less ADH into the blood
-less ADH means that the DCT and collecting duct are less permeable, so less water is reabsorbed into the blood by osmosis
-a large volume of dilute urine is produced and more water is lost
Describe in detail the sequence of events of how ADH actually works (dehydration)
-ADH attaches to receptors on cell membranes of cells lining the collecting duct
-this triggers the formation of a “2nd messenger” inside the cells (cyclic AMP), which causes a cascade of events
-inside the cells lining of the collecting duct are vesicles which contain protein-water channels (aquaporins)
-these vesicles move to and fuse with the cell membranes of the cells lining the collecting duct
-the aquaporin channels are then inserted into the cell membranes, making the membranes more permeable to water
-this provides a route for water to move out of the collecting duct and into the tissue fluid around the nephron, then back into the nearby blood capillaries, by osmosis
-so more water is saved, less urine produced, at a small volume and more concentrated
What happens when the water potential of the blood increases?
Fewer aquaporins are inserted into the membranes of the cells lining the collecting duct
