Renal 1 Flashcards
In a 70kg person, what is the:
TBW?
ICF?
ECF?
Intravascular Fluid?
Extravascular Fluid?
Plasma?
TBW- 42L
ICF-28L (40% of weight)
ECF- 14L (20% of weight)
IVF-4.9L (7% of weight)
EVF-11L (75% of ECF)
Plasma- 3L (25% of ECF)
What percentage of CO perfuses the kidneys (RBF)?
20%
What percentage of renal blood flow (RBF) is renal plasma flow (RPF)?
55%
What percentage of renal plasma flow (RPF) is GFR?
20%
When ECF volume expands how does the kidney compensate?
increases Na output and therefore water output leading to ECF volume contraction –> compensatory decrease in Na and water output ***This does not change GFR**
Which solute in the ECF primarily determines ECF volume?
Na+ (more Na, more ECF volume)
How is Na balance regulated?
adjust urine Na output to match Na intake (Na intake restricted –> gradually increasing Na reabsorption until lower Na output in urine is achieved)
Severe ECF volume contraction (dehydration) can cause a decrease in what renal paremeter?
GFR
When Na intake is reduced, to what extent does the ECF volume contract?
ECF volume contracts in an amount equivalent to the volume of urine needed to eliminate the excess Na isosmotically
How does the circulating volume change in edema and what does it do physiologically?
-decreases
Edema –> decrease circulating volume –> decrease renal perfusion pressure —> activates RAAS –> increase Na retention –> maintain edema
How are hydrostatic and oncotic pressures altered when diuretics are used to treat edema?
Hint: Diuretic –> increased Na + H2O elimination –> ?
increased elimination of Na and water
- -> decrease in hydrostatic pressure and increase in oncotic pressure
- -> absorption of edema
Renal Handling equation
Excretion = Filtration - Reabsorption + Secretion
Where is the proximal tubule located?
What does it reabsorb, and how?
- in the cortex
- reabsorbs 66% of filtered Na, 67% of K+ and most of filtered Bicarb
- This is a leaky epithelium so reabsorption is isosmotic and 66% of the filtered water is also reabsorbed
Where is the loop of henle located? What does it reabsorb? What transporter is used? What does this reabsorption accomplish?
- thin desc. and asc. in med, thick ascend, in medulla and cortex
- 25% of filtered Na, and 20% of K+ reabsorbed in thick asc limb Na/K/2Cl contransporter w/o water** –> drives the counter current multiplication of interstitial solute concentration
Where is the distal tubule located?
Describe its H2O permeability.
What is functionally unique about the late DT? What is its function, and what transporters are used? This transporter is the target of what type of diuretics?
- cortex
- impermeable to H2O
- late DT is last part of nephron to control ion composition of urine
- reabsorption of 6% of filtered Na via Na/Cl cotransporter at luminal membrane and Na/K ATPase at basolateral membrane **Na/Cl cotransporter is target of thiazide diuretics**
Where is the collecting duct located and what is its function?
- outer cortex and inner medulla
- reabsorption of water induced by ADH
How is the fractional excretion of water calculated? (FEwater)
= urine flow rate (V)/GFR
-fraction of glomerular filtrate not reabsorbed from the tubular fluid
Which hormone regulates Na reabsorption and K+secretion in the distal tubule? Water reabsorption?
Aldosterone
ADH
What is the filtration fraction?
fraction of plasma flowing through the glomeruli which is ultrafiltered to form tubular fluid
(GFR/RPF) ~.20 (20%)
How can the fractional excretion of any ion be calculated?
How can the clearance of any ion be calculated?
FEx = Cx / Ccreat
Cx = (Ux)(V) / Px
((Ux = [x] in urine; Px = [x] in plasma))
In which 2 areas of the nephron is K+ reabsorbtion/secretion NOT affected by dietary K+ intake? which areas are affected by dietary K+ intake?
NOT affected
- proximal tubule
- thick ascending loop of henle
Affected
-distal tubule and collecting duct
When in water and Na balance, approximately how much of the filtered water and Na is in the urine?
1%
What is the effect of alkalosis on K+ secretion? Acidosis? Diuretic induced increase in tubular flow?
- alkalosis –> increases K+ secretion
- acidosis –> decreases K+ secretion
- Diuretic induced increase in tubular flow –> increases K+ secretion
How does the level of Na+ affect the secretion of K+? ***Very important point from lecture***
-an increase in Na+ reabsorption in the late distal tubule and collecting duct is functionally linked to an increase in K+ secretion –> increase in K+ excretion
**This is why patients taking loop diuretics are at risk for hypokalemia and instructed to increase their K+ intake
What happens in positive K+ balance?
- induced by normal or high K+ diet
- increased secretion and decreased reabsorprtion of K+
What drives the Ca and Mg reabsorption across the tubular epithelium in the thick ascending loop of henle?
- K+ leaks back into tubule lumen after being reabsorbed by Na/K/2Cl cotransporter
- Cl- efflux across basolateral membrane –> Lumen + potential difference –> drives Ca and Mg reabsorption
When in NEGATIVE water balance, approximately how much of the filtered water is in the urine?
<1%
When in POSITIVE water balance, approximately how much of the filtered water is in the urine?
>1%
What happens in negative K+ balance?
- it is induced by a low K+ diet
- decreased secretion and increased reabsorption of K+
The solute reabsorption in the thick and thin ascending loop of henle without water reabsorption leads to….
dilution of the tubular fluid and the capacity to make a dilute hyposmotic urine
Does ADH increase or decrease in response to an INCREASE in plasma osmolarity?
ADH increases with increase osmolarity –> retention of water –> hypertonic urine (- free water clearance)
Does ADH increase or decrease in response to a DECREASE in plasma osmolarity?
ADH decreases with decrease in osmolarity –> elimination of free water by kidney –> hypotonic urine (+ free water clearance)
How does Aldosterone affect the late distal tubule?
1) diffuses into the cell from basolateral membrane
2) binds intracellular receptor
3) enters nucleus and induces transcription of mRNA for membrane transport proteins mediating Na reabsorption
4) increased Na reabsorption
What does a hypertonic urine indicate?
the kidney is responding to ECF volume contraction by retaining water in excess of solutes (free water)
What does hypotonic urine indicate?
the kidney is responding to ECF volume expansion by excreting water in excess of solutes (free water clearance)
When C h2o (free water clearance) is equal to 0 is the urine hypotonic, isotonic, or hypertonic? >0?
=0 - urine is isotonic
>0 - urine is hypotonic
What is free water clearance (C h2o) defined as?
the rate at which the kidney can retain or eliminate water free of solutes
