renal - lecture 4 Flashcards
define hypoosmotic
having total solute conc less than that of normal extracellular fluid = 300 mosm
define osmolarity
total solute concentration of a solution
measure of water concentration = the higher the osmolarity = lower the water concentration
define isoosmotic
having total solute conc equal than that of normal extracellular fluid
define hyperosmotic
having total solute conc greater than that of normal extracellular fluid
describe renal regulation of water balance
water freely filtered but 99% reabsorbed
majority of water reabsorption occurs ~2/3rds occurs in proximal tubule
major hormonal control of reabs occurs in cd
what does water reabs depend on
na reabs
passive not active
describe water reabs - figure
tubular lumen = higher
na + goes in
and decreases local osmolarity and then h20 goes towards isf para or transcellular and increases local osmolarity and then bulk flow reabsorbed back in body
describe process - 4 of water reabs
1 - na reabs from tubular lumen to the isf across epithelial cells
2 - local osmolarity in lumen decreases while local osmolarity in interstitium increases
3 - difference in osmolarity causes net diffusion of water from lumen into isf via tubular cells plasma membranes or via tight junctions
4 - from interstitium water sodium and everything else dissolved in isf move together by bulk flow into peritubular cap
describe maintenance of water balance
has to maintain
when intake of water small = kidney reabsorbs more water = less urine 0.4l/day = bare minimum
when water intake is large = kidney reabsorbs less water = urine outpur 25l/day
where does dynamic regulation take place of water
in cd - cortical and meduallry
describe components of dynamic regulation
high osmolarity of medullary interstitium
permeability of cd to water = regulated by vasopressin
describe urine concentration
contercurrent multipler system = allows build up of solutes in medullary interstitium
kidney has ability to concentrate urine up to 1400 mosm/l
urinary concentration takes place as tubular fluid flows through medullary collecting ducts
urinary concentration depends on hyperosmolarity of isf
in presence of vasopressin = water diffuses out of ducts into isy in medulla to be carried away = allows cells to be permeable to h2o
how does medullary interstitial fluid become hyperosmotic
Through the function of henles loop
describe how medullary interstitial fluid become hyperosmotic
descending limb = down flow and ascending = up flow
creates countercurrent flow
describe countercurrent multiplier system - step 1 ascending
ascending = actively reasbs nacl but impearmeble to h2o
becomes hypoosmotic since h20 cannot follow sodium since tjs tight
200mosm
describe countercurrent multiplier system - step 2 descending
descending = does not reabs nacl but permeable ro water
enters as 300mosm but becomes hyperosmotic = 400mosm
describe countercurrent multiplier system - move and after move
now goes from 200 –> 400 at ascending =
Beginning of gradient
osmolarity increases as go down and decreases as go up
describe countercurrent multiplier system - 2nd cycle
now bc sodium reabsorbed = 300 mosm
but interstitial = 500 mosm
in descending = always the same conc as interstitium
describe countercurrent multiplier system - move to continue
becomes more concentrated as go down = since permeable to waste
1400 = highest possible
diff for diff animals
usually ends up as 100mosm at dct = v low
describe vasa recta
branch of periubular cap
bv in medulla
hairpin loop structure = minimizes excessive loss of solute from interstititum
also to nacl, urea contibutes to medullary hyperosmolarity
what what does water reasb depend on
water permeability of tubules
what does permeability of epithelium depend on
depends on tubular segment = where
proximal tubule= high permeability to water, not regulated
permeability largely depends on presence of water channels = aquaporins in plasma membrane
what is water permeability regulated by
regulated by amount of aquaporins in pm
in ccd and mcd = subject to physiological control by hormone vasopressin
describe hormonal control
by vasopressin
in ccd and mcd
what is vasopressin
peptide hormone aka adh
produced by group of hypothalamic neuron’s
released from posterior pit lobe of pituitary gland
couples to gpcr v1 (smooth muscle) and v2 (kidney)
what does vasopressin do
stimulates insertion of aquaporins in luminal membrane of collecting duct cells and increases water permeability
v2 binds vasopressin in kindey = aquaporins inserted into tubular side which has water channels = suddenly cells permeable
describe when vasopressin present
collecting ducts become more permeable to water = reabs
very vigorous since high osmolarity
describe when. vasopressin not present
collecting ducts become impermeable to water = water diuresis
osmolarity does not matter
what is diabetes insipidus
Caused by malfunction of vasopressin system = vassopresin does not work or if do receptors not working = massive water diuresis
describe concentrations with vasopressin
300-1400
normal
describe concentrations without vasopressin
very extreme scenario
50 all the way down
since no water reabs
describe regulation of vasopressin
water excretion mainly regulated by rate of water reabs from tubules
Vasopressin regulates this rate
so vasopressin is a major regulator of water excretion
name 2 mechanisms to regulate vasopressin secretion
osmoreceptor control = most important
baroreceptor control = less sensitive
describe osmoreceptor control of vasopressin secretion
excess h20 ingested = decrease body fluid osmolarity = firing by hypothalamic osmoreceptors - where vasopressin made = decrease vasopressin from post pit = decrease plasma vasopressin= decreased tubular permeability to h2o and decrease h2o reabs at collecting ducts = increase h2o secretion
describe baroreceptor control of vasopressin secretion
decrease plasma vol = decreased venous, atrial and arterial pressures (reflexes mediated by baroreceptors) = increase vasopressin secretion from post pit = increase plasma vasopressin =.increased tubular permeability to h2o and increase h2o reabs at collecting ducts = decrease h2o secretion
why do we feel thirsty
does not matter if vasopressin working if do not drink water
most important = increase plasma osmolarity –> osmoreceptors. –> stimulate thirst
decrease plasma vol –> baroreceptors –> increase angiotensin 2 –> increase thirst
dry mouth and throat stimulate thirst
metering of water intake by git = when git feels water = immediately no more thirst, this LOWERs thirst, becomes less sensitive with age = why old ppl die since do not feel thirsty
what happens when severe sweating
loss of water and salt = loss of hypoosmotic salt soln –> decrease plasma vol and increase plasma osmolarity (decreased h2o concentration)
decreased plasma vol = decreases gfr and increases plasma aldosterone –> decrease sodium excretion
(also acts to increase plasma vassopressin)
increase plasma osmolarity (decreased h2o concentration) = increase plasma vasopressin and decreases h2o excretion
= all part of reflexes
IMPORTANT = loss of water>loss of na
so Pna increases 150meq/l usually = 140meq/l
does not mean more sodium in body just proportional to water
