Regulation of Sodium Balance and ECFV (Rao) Flashcards
Why is it important to regulate ECFV?
it determines PV which determines mean circulatory filling pressure = cardiac output
What determines ECFV?
Na balance/intake
ECFV is INDEPENDENT of Plasma [Na]
What keeps plasma [Na] constant?
AVP/vassopressin-mediated water excretion by kidney
When is the only time plasma [Na] will change?
when gain or loss of Na exceeds thirst mechanism and kidney’s ability to correct the situation
If a person retains 1 day’s worth of Na (150 mEq) how much weight will they gain?
1 kg (from 1 L of H2O retained)
What does change in BW over a short period of time indicate?
Na retention
Why is BW monitored on a daily basis for pts on dialysis/renal failure?
used to calculate how much dialysis is needed/how much fluid they are retaining
What can cause a Na+ imbalance?
excessive sweating
diarrhea
diuretics
Is sweat isotonic?
1/2 isotonic
Is vomit isotonic?
yes
How is most of the Na excreted?
renal
How many mmoles of Na is put into the body per L of saline?
150 mmole
How many mEq of Na are reabs at each part of the nephron?
glomerulus, PT, LOH, DT/CD
glomerulus: 25,000 mEq
PT: 16,000 (64%)
LOH: 7,000 (28%)
DT/CD: 1750 (7%)
How much Na is excreted/day?
150-200 mEq or 1.5%
What signs are seen with ECFV deficit?
- hypotension (drop systolic and diastolic) with inc pulse
- dec orthostatic hypotension
What signs are seen with moderate to severe ECFV expansion?
- edema
- CHF or CRF
- heart sounds = S3 gallop (from inc venous congestion)
- venous distension in neck
What is a sign of a more severe inc in ECFV?
pulmonary edema = hearing ascultation of lungs or seen in CXR
What does hypo-albuminemia + edema with normal or low ECFV indicate?
liver disease
nephroptic syndrome
_____ determines the distribution of fluid between the ISF and plasma
starling forces
Why does dec plasma albumin cause edema?
- > dec colloid pressure -> fluid goes into ISF –> edema
* *but with reduced PV
Are burn pts edematous?
yes, they have inc endothelial permeability which leads to a flux of albumin and fluid into ISF
Does the body react faster to changes in Na input or to changes in plasma osmolarity from water intake?
plasma osmolarity changes due to water intake
1-2 hrs vs 2-4 days
What mechanisms respond to inc water intake?
thirst and ADH or AVP
What determines ECFV?
salt intake
Will ECFV inc or dec with a higher salt intake?
inc
Why are hypertensive pts recommended to restrict salt intake?
low salt intake decreases ECFV -> dec PV -> dec BP
What are salt-sensitive hypertensives?
pts that cannot correct hypertension with salt restriction alone. They need diuretics
How does our body sense an inc or dec in ECFV?
we have stretch and baroreceptors in large veins, atria, and arteries
What are the 3 types of ECFV receptors?
where are they?
Neural stretch
atrial stretch
arterial baroreceptor
Neural stretch receptors:
Where are they?
What specifically do they respond to?
Describe their response to this stimulus.
in large veins
respond to mechanical stretch due to venous distention
signals to pituitary gland to regulate AVP/ADH –> regulates Na+ excretion at NK2C channel of TALH
Atrial stretch receptors:
Where are they?
What specifically do they respond to?
Describe their response to this stimulus.
in atria
respond to distension
Elevated arterial pressure
- ->dec ADH secretion via parasympathetic nerve impulses.
- ->secrete ANP when the sense distension (promotes Na and H2O excretion)
Arterial baroreceptors:
Where are they?
What specifically do they respond to?
Describe their response to this stimulus.
in arteries
respond to inc pulse pressure or arterial BP
signals to pituitary to regulate AVP and renin
Changes in GFR result in proportional changes in the filtered load of ___
Na (therefore changing GFR will change Na excretion)
Why can small changes in GFR cause a big change in the amt if Na excreted?
if you inc GFR by 10%, you will inc the FL of Na. Without a change in reabs of Na, more Na will be delivered to the LOH which will be passed along to the DT and CD and be excreted
*however, glomerulotubular balance functions such that Na reabs will always inc–ensuring a constant FRACTION is reabs
What is pressure natriuesis and how does it regulate ECFV?
When BP gets too high, pressure naturesis will cause and inc in GFR to inc Na excretion in urine to decrease BP and correct ECFV
It is a compensatory mechanism to maintain blood pressure within the normal range.
How is the effect of pressure naturesis different in an isolated kidney vs an intact system?
isolated: has an acute effect (2-3 fold inc in Na output by 30 to 55mmHg change in arterial pressure) = independent of sympathetic and hormonal regulation
Intact system: very effective and is syndergized with reduced formation of renin, angiotensin II, and aldosterone
None of this made any sense to me, so I just copied the notes, so this could be wrong/incomplete
What secretes aldosterone?
adrenal cortex
What stimulates the release of aldosterone from the adrenal cortex?
inc plasma K+
angiotensin (dec in ECFV–> renin release –> ang made)
What inhibits the release of aldosterone from the renal cortex?
inc plasma Na
Where does aldosterone act?
DCT and CD
T or F: Inc in aldo decreases Na reabsorption
F: aldo increases Na reabs
What is the MOA of aldosterone?
Acts on minearalcorticorticoid receptors (MR) in principal cells of DCT and CD to alter gene expression…
- inc apical Na channels (lumen -> cell)
- inc basolateral Na-K ATPase
- inc K apical channels (cell -> lumen)
- inc kreb’s cycle enzymes to inc ATP synthesis (which is needed for the new NaKATPases)
- inc NKA- to inc Na reabs and K+ secretion (charges?)
Aldosterone (slowly or rapidly) affects the reabs of Na.
slowly
Will aldosterone play a role in the rapid regulation of Na+ excretion?
no (it works slowly to cause Na reabs)
What is the source of ANP?
cells in cardiac atria
What stimulates the secretion of ANP?
atrial distention (directly) inc plasma Na (indirectly)
What is the target of ANP?
afferent and efferent arterioles
tubules
What are the actions of ANP?
GOAL is to inc Na excretion by…
- inhibits Na reabs in tubules
- dilates afferent arteriole and constricts efferent arteriole to increase GFR and inc Na excretion
- inhibits aldosterone secretion from adrenal cortex
What stiulates the renin-angiotensin system?
dec BP
dec ECVF
inc sympathetic firing
What is the MOA of renin and the renin-ang sys?
secreted by JG cells and converts alpha-2 globin to ang I which gets converted to Ang II by ACE in the PT
Ang II
1. inc aldo production in adrenal cortex
2. activates PT Na:H exchanger
= both inc Na reabs
Once the ECFV has exapanded enough, the BP has been restored and the JG cells stop making renin and system is turned off
What inhibits the renin-ang sys?
high Na (bc ECFV is high –> JG cells sense that volume is not low anymore and stops making renin)
How does sympathetic nerve action affect Na reabs/ECFV?
constricts/dialates arterioles to
dec GFR –> inc Na reabs
inc GFR –> dec Na reabs
What effect does prostaglandins, bradykinin, and dopamine have on Na retention/ECFV? WHere are these made?
they diurese and natriurese
made in kidney
What is quabain like factor?
inhibits NaK-ATPase to inc Na excretion
produced in the atrium and plants
*not well understood
How are the receptors of ecfv similar and how are they different?
All 3 regulate AVP secretion for pituitary
Neural are in veins
Atrial are in atria and also secrete ANP
Arterial are in arteries
