Intro to GFR/RBF Flashcards
What 3 layers must filtrate pass through at the glomerulus?
Capillary endothelium
Glomerular basement membrane
Podocyte epithelium
Where is the biogel? What is it made of?
At the glomerular endothelium glycocalyx.
Hyaluranon, heparan sulfate.
Nephrin
Anchoring protein at the slits between foot processes.
Decreases in nephrin is associated with renal disease.
What passes freely through the filtration barrier?
Water Small solutes (Glc, AA, electrolytes)
Concentrations must be equal on both sides of the membrane.
What is NOT freely filtered at the filtration barrier?
Proteins
Cells
Tamm-Horsfall protein
Most abundant protein in urine.
Produced in the thick ascending loop of Henle.
What charges filter the easiest?
Cations best, then neutral, then anions.
What diseases commonly cause a damaged filtration barrier? (4)
Hematuria/Proteinuria
Diabetic nephropathy
Minimal change disease
Nephropathy
The cortex contains: (3)
Renal corpuscles
Coiled BVs
Coiled tubules
Random arrangement
The medulla contains: (2)
Straight BVs
Straight tubules
More organized.
What happens to RBF during intense exercise?
Renal fraction of BF decreases because blood is shunted to the muscles.
Filtered load of X =
Plasma conc. of X x GFR
Urinary excretion =
Amt. filtered - amt. reabsorbed + amt. secreted
Tubular resorption =
Glomerular filtration - urinary excretion + amt. secreted
How do we know if tubular secretion occurred?
If excretion > filtration
Urinary excretion rate =
V =
Ux x V
Urinary conc. x urine flow rate
urine vol./time
Renal clearance
The volume of plasma completely cleared of a substance by the kidneys per unit time.
Renal clearance =
(conc. of X in urine x urine flow rate)/conc. of X in plasma
Cx = (Ux x V)/Px
Glomerular filtrate
Volume of plasma filtered into the combined nephrons of both kidneys per unit time.
Filtered across the glomerular capillaries into the Bowman’s capsule.
Protein and cell free.
FF =
GFR/RPF
FF
Fraction of RBF that is filtered across the glomerulus.
Changes with ultrafiltration pressure.
What is the relationship between the locations along the glomerular capillary and oncotic pressures?
Why?
Oncotic pressures increase from arterial end to efferent end due to fluid leaving and increasing the conc. of proteins inside the capillary.
What is the relationship between oncotic pressure of the efferent arteriole and FF?
Direct relationship.
Filtered load vs FF
Filtered load is a rate at which substance passes through the glomerulus.
FF is the ratio of GFR to RBF.
Reabsorption =
Filtered load - excretion
Generally quite high
Inulin
Can be used to determine renal clearance or GFR because it is not reabsorbed or secreted AND the amount filtered is the same as the amount that is secreted in urine.
GFR can be swapped for:
Renal clearance
(Ux x V)/Px
Using creatine for clearance estimate
From metabolism of creatine phosphate in muscle
Dependent on age and muscle mass
Production = excretion
Useful for longterm monitoring
However, 10% of the excreted creatine is secreted.
3 methods of sympathetic stimulation at the kidney to increase BP
SM: Powerful vasoconstriction (afferent > efferent arteriole) via a1 receptors.
JG cells: Renin release (RAAS system) via B1 receptors.
Tubular epithelial cells: Na/K ATPase (increased Na reabsorption) via a1 receptors
Longterm effects of sympathetic stimulation at the kidney
Decreased urinary output
Decreased urinary Na excretion
Increased water intake
Relationship between [creatinine] and GFR:
Inverse relationship.
As GFR increases, plasma [creatinine] goes down.
> 20:1 BUN: creatinine ratio
Prerenal
Hypovolemia, dehydration, reduced renal perfusion, high protein diet
10-20.1 BUN: creatinine ratio
Normal or postrenal
<10:1 BUN: creatinine ratio
Intrarenal
Liver disease
Low protein diet
PAH
Can be used to estimate RBF, but is troublesome because it must be administered IV.
