alimentary mechanisms Flashcards
hydration: recall the hormonal control of water balance
what are sensing organs for solute concentration and where are they located
osmoreceptorsin brain adjacent to structures with incomplete blood brain barrier to sample ECF (hypothalamus, within organum vasculosum and subfornical organ regions)
what do peripheral baroreceptors respond to
changes in blood volume and pressure so are less sensitive
threshold for response: increased osmolarity
2-3%
threshold for response: decrease in volume and/or arterial pressure
10-15%
where is vasopressin produces and released from
produced in hypothalamus and released from posterior pituitary gland
2 functions of vasopressin
insert aquaporin-2 channels into collecting duct to increase water reabsorption, stimulate vasoconstriction
effect of actions of vasopressin
conserve blood volume and increase blood pressure
what else do these mechanisms stimulate besides water retention
thirst
how do osmoreceptors respond to reduced and increase osmolarity and how
reduced will grow, increased will shrink; by osmosis
what do changes in size of osmoreceptor affect, and what will this adjust
firing rate, which will adjust basal level of ADH secreted
how can thirst be satiated using short-term feedback
even in presence of water, GIT can quench thirst from receptors in upper GIT (mouth to oesophagus) - before plasma osmolarity decreases
how can thirst be satiated using long-term feedback
once original stimulus of osmolarity, blood pressure or arterial pressure corrected, perception of thirst no longer felt
5 primary effects of angiotensin II
binds to receptors on VSMCs to stimulate vasoconstriction; upregulates activity of sympathetic nervous system to promote vasoconstriction; stimulates aldosterone secretion which increases Na+ reabsorption, creating osmotic gradient; directly influences Na+ reabsorption, causing water reabsorption; stimulates ADH release and thirst
what else does angiotensin II activate
SFO (subfornical organ) neurones in hypothalamus
