renal - lecture 4

Question 1

define hypoosmotic

Answer 1

having total solute conc less than that of normal extracellular fluid = 300 mosm

Question 1

define osmolarity

Answer 1

total solute concentration of a solution
measure of water concentration = the higher the osmolarity = lower the water concentration

Question 2

define isoosmotic

Answer 2

having total solute conc equal than that of normal extracellular fluid

Question 3

define hyperosmotic

Answer 3

having total solute conc greater than that of normal extracellular fluid

Question 4

describe renal regulation of water balance

Answer 4

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

Question 5

what does water reabs depend on

Answer 5

na reabs
passive not active

Question 6

describe water reabs - figure

Answer 6

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

Question 7

describe process - 4 of water reabs

Answer 7

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

Question 8

describe maintenance of water balance

Answer 8

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

Question 9

where does dynamic regulation take place of water

Answer 9

in cd - cortical and meduallry

Question 10

describe components of dynamic regulation

Answer 10

high osmolarity of medullary interstitium
permeability of cd to water = regulated by vasopressin

Question 11

describe urine concentration

Answer 11

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

Question 12

how does medullary interstitial fluid become hyperosmotic

Answer 12

Through the function of henles loop

Question 13

describe how medullary interstitial fluid become hyperosmotic

Answer 13

descending limb = down flow and ascending = up flow
creates countercurrent flow

Question 14

describe countercurrent multiplier system - step 1 ascending

Answer 14

ascending = actively reasbs nacl but impearmeble to h2o
becomes hypoosmotic since h20 cannot follow sodium since tjs tight
200mosm

Question 15

describe countercurrent multiplier system - step 2 descending

Answer 15

descending = does not reabs nacl but permeable ro water
enters as 300mosm but becomes hyperosmotic = 400mosm

Question 16

describe countercurrent multiplier system - move and after move

Answer 16

now goes from 200 –> 400 at ascending =
Beginning of gradient
osmolarity increases as go down and decreases as go up

Question 17

describe countercurrent multiplier system - 2nd cycle

Answer 17

now bc sodium reabsorbed = 300 mosm
but interstitial = 500 mosm
in descending = always the same conc as interstitium

Question 18

describe countercurrent multiplier system - move to continue

Answer 18

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

Question 19

describe vasa recta

Answer 19

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

Question 20

what what does water reasb depend on

Answer 20

water permeability of tubules

Question 21

what does permeability of epithelium depend on

Answer 21

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

Question 22

what is water permeability regulated by

Answer 22

regulated by amount of aquaporins in pm
in ccd and mcd = subject to physiological control by hormone vasopressin

Question 23

describe hormonal control

Answer 23

by vasopressin
in ccd and mcd

Question 24

what is vasopressin

Answer 24

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)

Question 25

what does vasopressin do

Answer 25

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

Question 26

describe when vasopressin present

Answer 26

collecting ducts become more permeable to water = reabs
very vigorous since high osmolarity

Question 27

describe when. vasopressin not present

Answer 27

collecting ducts become impermeable to water = water diuresis
osmolarity does not matter

Question 28

what is diabetes insipidus

Answer 28

Caused by malfunction of vasopressin system = vassopresin does not work or if do receptors not working = massive water diuresis

Question 29

describe concentrations with vasopressin

Answer 29

300-1400
normal

Question 30

describe concentrations without vasopressin

Answer 30

very extreme scenario
50 all the way down
since no water reabs

Question 31

describe regulation of vasopressin

Answer 31

water excretion mainly regulated by rate of water reabs from tubules
Vasopressin regulates this rate
so vasopressin is a major regulator of water excretion

Question 32

name 2 mechanisms to regulate vasopressin secretion

Answer 32

osmoreceptor control = most important
baroreceptor control = less sensitive

Question 33

describe osmoreceptor control of vasopressin secretion

Answer 33

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

Question 34

describe baroreceptor control of vasopressin secretion

Answer 34

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

Question 35

why do we feel thirsty

Answer 35

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

Question 36

what happens when severe sweating

Answer 36

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