5.2.7 Osmoregulation Flashcards
What is ADH?
Antidiuretic hormone, hormones that controles the permeability of the collecting duct
What is an osmoreceptor
A sensory receptor that detects changes in water
What is osmoregulation?
Control of water potential in the body, involves controlling levels of both water and salt in the body
Why must there be a correct water balance
To prevent water entering cells and cuasing lsis or leaving cells and causing crenation
Where does the body get its water from?
Food, drink and metabolism (e.g respiration)
How is water lost in the body?
Urine, sweat, water vapour in exhaled air and faeces
What is the mechanism behind osmoregulation?
1) If you need to conserve LESS water, walls of collecting ducts become less permeable –> This means that less water is reabsorbed and a greater volume of urine will be produced
2) If you need to conserve MORE water, the collecting duct walls are more permeable –> more water can be reabsorbed into the blood –> Less urine is produced
How is the permeability of the collecting duct altered?
1) Cells in walls of collecting duct respond to levels of ADH in the blood –> These cells have membrane bound receptors for ADH.
2) ADH binds to these receptors, causing a chain of enzyme controlled reactions inside the cell. (Example of cell signalling)
3) End result of these reactions is to cause vesicles containing water-permeable channels (aquaporins) to fuse with cell surface membrane –> Walls more permeable to water
4) Levels of ADH rising in blood = more water permeable channels inserted –> More water to be reabsorbed by osmosis, into blood. Less urine produced and urine has a lower water potentional
5) If levels of ADH in blood falls, cell surface membrane folds inwards (invaginates) to create new vesicles that remove water-permeable channels from the membrane. –> Less water is reabsorbed by osmosis into blood–> More water passes down collecting duct to form a great volume of urine which is more dilute (high w.p)
Where is ADH manufactured and how are they released?
1) Neurosecretory cells, found in cell body which lies in the hypothalamus.
2) ADH moves down axon to the terminal bulb in the posterior pituitary gland where it by osmoreceptors then carry action potentials down their axons and cause the release of ADH by exocytosis.
3) Entering blood capilaries running through the pituitary gland. –> Transported around body and acts on target cells of the collecting duct.
4) When water level rises less ADH is released –> Broken down and the collecting duct will receive less stimulation
