5.2.7 osmoregulation Flashcards
antidiuretic hormone (ADH)
hormone which control permeability of collecting duct walls
osmoreceptor
sensory receptor that detects changes in water potential
osmoregulation
control of water potential in body (includes salts too)
3 sources of water
- food
- drink
- metabolism (eg. respiration)
4 ways water is lost from the body
- urine
- sweat
- water vapour in exhaled air
- faeces
what do the kidneys act as
effector to control water content of body & salt concentration in body fluids
mechanism of osmoregulation: conserving less water (cool day/hydrated)
- walls of collecting duct become less permeable
- less water reabsorbed
- greater volume of urine produced
mechanism of osmoregulation: conserve more water (hot day/dehydrated)
- collecting duct walls made more permeable
- more water reabsorbed into blood
- produce smaller volume of urine
what do the cells in the walls of the collecting duct have
membrane-bound receptors for ADH
effect of ADH on membrane-bound receptors in cell walls of collecting duct
- ADH binds to receptors & causes chain of enzyme-controlled reactions inside cell
- end result = cause vesicles containing water-permeable channels (aquaporins) to fuse will cell surface membrane
- makes walls more permeable
aquaporins
water-permeable channels
what happens when levels of ADH in blood rises
- more water-permeable channels inserted
- allows more water to be reabsorbed by osmosis (into blood)
- less urine produced & has lower water potential
what happens when levels of ADH in blood falls
- cell surface membrane folds inward (invaginates) = creates new vesicles to remove water-permeable channels from membrane
- makes walls less permeable & less water reabsorbed by osmosis (into blood)
- more water passes down collecting duct = greater volume of urine which is more dilute (higher water potential)
summary of effect of ADH on wall of collecting duct
- ADH detected by cell surface receptors
- chain of enzyme-controlled reactions
- vesicles containing aquaporins fuse to membrane
- more water reabsorbed
what does the hypothalamus in the brain contain
specialised cells = osmoreceptors
what do osmoreceptors respond to & how
effects of osmosis
- water potential in blood low (negative) = osmoreceptor cell loses water by osmosis & shrinks
- stimulate neurosecretory cells in hypothalamus
neurosecretory cells
- what are they
- how do they produce ADH
= specialised neurones which produce/release ADH
- ADH manufactured in cell body (lies in hypothalamus)
- ADH moves down axon to terminal bulb in posterior pituitary gland
- stored in vesicles
- when stimulated by osmoreceptors = carry action potential down axons & cause release of ADH by exocytosis
what is osmoregulation an example of
negative feedback
negative feedback: increase of water potential in blood
- detected by osmoreceptors in hypothalamus
- less ADH released from posterior pituitary gland
- collecting duct walls less permeable
- less water reabsorbed into blood & more urine produced
= decrease in water potential of blood
negative feedback: decrease of water potential in blood
- detected by osmoreceptors in hypothalamus
- more ADH released from posterior pituitary gland
- collecting duct walls more permeable
- more water reabsorbed & less urine produced
= increase in water potential of blood
how is ADH transported from the posterior pituitary gland to the collecting duct
- ADH enters blood capillaries running through posterior pituitary gland
- transported around bound & acts on cells of collecting ducts
