Osomoregulation Flashcards
What is antidiuretic hormone (ADH)?
A hormone that controls the permeability of the collecting duct walls.
What is an osmoreceptor?
A sensory receptor that detects changes in water
What is osmoregulation?
Osmoregulation is the control of the water potential of the body.
What does osmoregulation involve?
It involves controlling the levels of both water and salt in the body.
What are the three sources that the body gets water from?
Food, drink and metabolism (e.g. respiration).
How is water lost form the body?
Urine, sweat, water vapour in exhaled air, and faeces.
How do the kidneys alter the amount of urine produced?
By altering the permeability of the collecting membrane.
What happens on a cool day?
The walls of the collecting duct becomes less permeable. This means that less water is reabsorbed and a greater volume of urine will be produced.
What happens on a hot day?
The walls of the collecting duct are made more permeable so that more water can reabsorbed into the blood. You will produce a smaller volume of urine.
How does the use of ADH effect the permeability of the collecting duct membrane?
ADH in the blood binds to membrane-bound receptors for ADH on the collecting duct membrane. This causes vesicles containing water-permeable channels (aquaporins) to fuse with the cell surface membrane. This makes the walls more permeable to water.
What happens if the level of ADH in the blood falls?
The cell surface membrane folds inwards (invaginates) to create new vesicles that remove water-permeable channels from the membrane. This makes the walls less permeable and less water is reabsorbed, by osmosis, into the blood.
What happens to the osmoreceptors when the water potential of the blood is negative?
The osmoreceptor cells lose water by osmosis and shrink. As a result they stimulate neurosecretory cells in the hypothalamus.
What are the neurosecretory cells and what do they do?
They are specialised neurones (nerve cells) that produce and release ADH.
How does the ADH move in the hypothalamus?
ADH moves down the axon terminal bulb in the posterior pituitary gland, where it is stored in vesicles. When the neurosecretory cells are stimulated by osmoreceptors, they carry action potentials down their axons and cause the release of ADH by exocytosis.
