Flashcards in PSL301: Water 2 Deck (80):
- Old man
- low BP
- Given ACE inhibitor
- Serum creatinine increased 100 -> 200
- GFR decreased by 50%
- Low BP caused by MI
- Low BP causes decreased afferent arteriole pressure
- Normally would be okay because ANG II will decrease efferent arteriole pressure
- ACE inhibitor stopped ANG II
Large volume of plasma is filtered through ___
Final urine =
amount filtered - amount reabsorbed + amount secreted
fluids & solutes enter the __ lumen
Function of tubules
reabsorb / secrete solute & water
Solutes & water is reabsorbed into...
The kidney is divided into...
Most of the blood supply to the kidney goes to the...
Number of nephrons in a kidney?
Where is the bowman's space located?
Between glomerulus and Bowman's capsule
What is shared between many nephrons?
The collecting duct
Passage of fluid in the nephron
1. Glomerulus / Bowman's capsule
2. Proximal convoluted tubule
3. Loop of Henle (descending & ascending limb)
4. Distal convoluted tubule
5. Collecting duct
___% of CO goes to the kidneys
20 - 25
The glomerulus is the only place that has...
efferent arteriole (instead of venule)
Purpose of the efferent arteriole
The efferent arterioles flow into...
1 nephron has 2 ___ and 2 sets of ____
The 2 arterioles of the nephron
The 2 sets of capillaries of the nephron
The capillary walls at the glomerulus has more ___ than normal
pores in the endothelium
What serves as a barrier to the Bowman's capsule lumen?
Glomerular basement membrane / podocytes
The filtered material in the glomerulus goes...
into the Bowman's Capsule lumen through filtration slits
Function of the glomerulus
Filter solutes, water into Bowman's space & proximal tubule
>90% of renal blood flow goes to ___ first through ___
What do the peritubular capillaries drain into?
Features of glomerular capillaries
- leaky to water
- muscular arterioles put blood in and take blood out
- contraction & dilation of afferent & efferent arterioles regulates GFR
The capillaries at the glomerulus is ___x more leaky
What regulates GFR?
contraction & dilation of afferent & efferent arterioles
Most important determinant of GFR
Renal blood flow
Renal blood flow is determined by...
- arterial BP (at heart)
- resistance (at the renal vessels)
Renal blood flow can be kept constant at what BP?
70 - 150 mmHg (systolic arterial pressure)
What is the main factor regulating renal blood flow?
myogenic reflex in the afferent arteriole
Myogenic reflex sensing decreased BP causes...
afferent arteriole to dilate
Myogenic reflex sensing increased BP causes...
afferent arteriole to constrict
What other factors are important at low blood pressure?
- ANG II
Effect of ANG II
Raise blood pressure
- efferent arteriole constrict
Effect of prostaglandins
Dilate afferent arteriole
What are the renal vasoconstricters?
- ANG II (efferent arteriole)
- Catecholamines (NE)
What are the renal vasodilators?
- high protein diet
What is one instance in which GFR changes? Why?
- Both GFR and blood flow increases by 25%
What happens to blood pressure during pregnancy?
Why might high protein diets cause renal arterioles to dilate?
Afferent arteriole constriction causes... (effect on GFR)
Decreased ____ = decreased GFR
capillary blood pressure
Efferent arteriole constriction causes... (effect on GFR)
Increased GFR (harder to leave capillaries)
GFR / RBF
Proportion of blood going into glomerulus that is filtered
Efferent arteriole constriction prevents...
drop in GFR when BP drops
ANG II increases ___
Increased filtration fraction =
Role of ANG II in terms of GFR
Keeps it high at lower BP
Value: normal GFR
What is affected during low blood pressure: BP, RBF, GFR, FF?
Filtration of solutes is determined by...
1. convection (hydrostatic pressure & bulk flow of water)
2. molecular weight
Cut offs for which molecular weight can be filtered and whatnot
< 15000 = freely filtered between plasma & Bowman's space
15000 - 60000 = only some are filtered
> 60000 = albumin = not usually filtered
What does finding albumin in the urine tell us?
Problems with kidney wall permeability
Which solutes are freely filtered?
Which solutes can't be filtered?
- Globulins (antibodies)
What is the best measure of kidney function?
Why is GFR such a good measure of kidney function?
- Correlates with clinical consequences of reduced kidney function
- Most kidney diseases affect the glomerulus
Units for GFR
Criteria for solute used to measure GFR
- freely filtered
- not reabsorbed / secreted by tubules
- amount filtered = amount excreted
- GFR = amount found in urine every minute
Why is glucose a bad measurement of GFR?
All glucose is reabsorbed
Why is urea a bad measurement of GFR?
50% of urea is reabsorbed
What is a good marker for GFR? Why?
Insulin (gold standard)
- no reabsorption
- filtration = excretion
MW of insulin
Problem with using insulin as a marker for GFR
Has to be given using intravenously
= GFR * [plasma x]
= urine flow rate * [urine x]
= urine flow rate * [urine x] / [plasma x]
What marker is usually used to measure GFR? How is it usually done?
Creatinine (24h urine sample)
Formula: GFR (using creatinine 24h urine sample)
= urine volume * [urine creatinine] / [plasma creatinine]
Creatinine is a good estimate for GFR only if...
- accurate urine collection
- production of creatinine = secretion
- serum creatinine is constant
If we want to be lazier than 24h urine sample, what can we do to measure GFR?
GFR = 1 / [plasma creatinine]
Plasma creatinine depends on...
- muscle mass
Disadvantage of measuring GFR from plasma creatinine
Differs depending on age, weight, sex...
What must we know to calculate GFR from plasma creatinine?
(this gives us the constant value)
What drug is associated with causing acute kidney failure?
GFR is usually autoregulated by...
afferent arteriolar tone