Flashcards in F214:02:07 Osmoregulation Deck (51):
What does ADH stand for?
What is ADH?
A hormone that increases the reabsorption of water in the collecting duct in the kidneys
Where is ADH released from/
The pituitary glands
What are osmoreceptors?
receptor cells that monitor the water potential of the blood
What happens in the blood has a low water potential ?
Water is moved out of the osmoreceptor cells, causing them to shrink, which alerts the neurosecretory cells
What is the hypothalamus?
The part of the brain which contains neurosecretory cells and various receptors which monitor the blood
What are neurosecretory cells?
specialised cells that act like nerve cells but release a hormone into the blood
ADH is manufactured in the cell body and passes down the axon to be stored in the terminal bulb.
If an action potential passes down th axon, then the ADH is released from the terminal bulb
Where is ADH stored?
In the terminal bulb of the neurosecretory axon
What do neurosecretory cells act like?
How are neurosecretory cells stimulated?
By an action potential passing down their axon.
What is the posterior pituitary gland?
the hind part of the pituitary gland, which releases ADH
Where are ADH receptors found?
In the membranes of cells that make up the walls of the collecting duct
NOT THE CELL WALLS
What is osmoregulation?
The control of water and salt levels in the body
Why must the water balance between cells and surrounding tissue fluid?
To prevent problems with osmosis
Name 3 sources of water
metabolism (eg respiration)
Name 4 examples of how water is lost
water vapour in exhaled air
How much urine would be produced if you drank alot of water on a cool day ?
a large volume of DILUTE urine
What helps to maintain the correct balance of water being lost in the collecting duct?
The fact that the walls of the collecting duct can be made more or less permeable depending on the needs of the body
What do the walls of the collecting duct respond to?
the level of ADH in the blood
How do the walls of the collecting duct detect levels of ADH in the blood?
Cells in the wall have membrane bound receptors for ADH
How does ADH cause a response?
it binds with receptors in the membrane and causes a chain ofenzyme-controlled reactions inside the cell
Which leads to vesicles containing water permeable channels to be inserted into the membrane
What happens once ADH has binded with receptors in the membrane and caused a chain of enzyme controlled reactions inside the cell?
vesicles containing water permeable channels are inserted into membrane
What effect does ADH have on the cell membrane?
causes it to become more fluid
What effect does ADH have on the amount of urine being produced?
The more ADH there is, the more water is reabsorbed into the blood, so less urine is produced, which had a lower water potential
What happoens if there is less ADH in the blood than normal?
cell surface membranes fold inwards to create new vesicles to remove water-permeable channels from the membrane
so the walls become less permeable and less water passes out
What is the water potential of the blood monitored by?
What do osmoreceptors respond to?
the EFFECTS of osmosis, ie they lose water by osmosis which causes them to shrink and stimulate the neurosecretory cells in the hypothalamus.
Where is ADH produced spefically in the in the neurosecretory cells?
in the cell body of these cells
Where does the cell body of neurosecretory cells lie?
in the hypothalamus
Where is the terminal bulb of the neurosecretory cells found?
in the posterior pituitary gland
Describe the 4 stages of how ADH has an effect on dealing with a lack of water in the blood
1. ADH is detected by cell surface receptors
2. Enzyme controlled reactions
3. Vesicles containing water permeable channels fuse to membrane
4. More water can now be reabsorbed
What is the name for the water permeable channels found in the wall of the collecting duct?
What is the half-life of a substance?
The time taken for its concentration to drop to half its original value
What does ADH act upon?
The cells of the collecting duct
What happens once ADH has taken effect and the water potential of the blood rises?
Less ADH is released
What is the half life of ADH?
about 20 minutes
Describe the negative feedback process when there is an increase in water potential of blood?
1. detected by osmoregulators in the hypothalamus
2. Less ADH released from posterior pituitary
3. collecting duct walls become less permeable
4. less water is reabsorbed into the blood and more urine is produced
5. There is a decrease in water potential in the blood
Describe the negative feedback process when there is a decrease in water potential of blood?
1. detected by osmoregulators in the hypothalamus
2. more ADH is released from posterior pituitary
3. Collecting duct walls become more permeable
4. More water is reabsorbed into the blood and less urine is produced
5. There is an increase in water potential in the blood
What effect does alcohol have on the kidneys?
it inhibits the production of ADH and certain antibiotics such as tetracycline which can cause renal failure through a variety of mechanisms
Give an example of an antibiotic that alcohol affects
How can alcohol cause renal failure?
Through a variety of mechanisms eg direct toxicity to the nephron tubules
Give an example of useful drugs that affect the work of the kindneys
What effect do diuretic drugs have on the body?
they increase urine production
What effect do antidiuretic drugs have on the body?
They decrease urine production by increasing the reabsorption of water at the distal tube and collecting ducts without significantly modifying the rate of glomerular filtration
How do neurosecretory cells differ from normal nerve cells?
Neurosecretory cells manufacture a hormone in their cell body; which is transferred down the axon.
When it is released it goes straight to the blood rather than to another nerve cell
Explain what is meant by negative feedback
negative feedback occurs when there is a change of internal conitions which stimulates a reversal of that change so that the conditions are kept constant
Why is it important that ADH is broken down?
So that it is not continually acting on the walls of the collecting duct
Explain why drinking too much can cause a hangover
Alcohol inhibits the action of ADH so the collecting ducts are very permeable to water, so dehydration occurs as the water is lost in the urine.
and the ethanal produced from the metabolism of ethanol also contributes to a headache.
Suggest what symptoms may be relieved by the use of diuretic drugs
Diuretic drugs can be used to relieve water retention which can cause swelling and high blood pressure.
Suggest what symptoms may be relieved by the use of antidiuretic drugs
Can be used to relieve diabetes insipidus and bed wetting