DSA- Introduction to Renal Blood Flow and GFR Flashcards
Describe 3-layered structure of the glomerular capillary filtration barrier
1) Capillary Endothelium
- Fenestrated
- permeable to water and small solutes in glomerulus
2) Glomerular Basement Membrane
- fibrous network of collagen, laminin, proteoglycan, glycoprotein
3) Podocyte Epithelium
- long, extending foot processes
- covered by a diaphragm
- form the walls of filtration slit
What is glycocalyx and what is the contribution to the barrier function of the endothelial surface layer?
- Negative-charged biogel like surface structure of proteoglycans
- glomerular endothelium
- lines interior of capillary lumen
- contains heparan sulfate and hyaluronan
- controls transcapillary fluid exchange
- biomechanical sensor
- provide molecular filling to fenestrate
What can freely filter in filtration barrier?
- water
- small solutes (glucose, amino acids, electrolytes)
- concentration equal on both sides of membrane
What can NOT freely filter in filtration barrier?
- large molecules (proteins)
- formed elements ( cells)
- Tamm-Horsfall protein
What is a Tamm-Horsfall protein? Where is it produced? function?
- glycoproteins not freely filtered in urine
- produced by the thick ascending loop of Henle
- prevent the crystallization of calcium in the nephron
- prevent urinary tract infections.
Filtration slits (Components, location, size range for filtration)
- Podocytes are held together by certain cell adhesion molecules.
- Nephrin (in slit) is often damaged in certain kidney disease states. It can also be mutated in some diseases.
- Molecules greater then 42 Å are not filtered
- molecules less than 20 Å are freely filtered.
Filtered components depend on… (2)
what about biogel?
1) Size
- smaller-> more freely filtered
2) charge
- more positive ions-> more freely filtered
More freely cleared =1
- bio-gel is negatively charged. As a result from that, negatively charged ions have a much more difficult time passing through the endothelium.
Components of the filtration barrier whose damage would result in hematuria
and proteinuria
-Physiological consequences a damaged filtration barrier would
have on body fluid oncotic and hydrostatic pressures.
Hematuria/proteinuria (presence of protein in urine)
- Damaged filtration barrier => larger proteins will exit through. => lose a lot of albumin
- decrease the colloid osmotic pressure of the capillaries => more water to enter into the interstitial tissue.
Summarize how anatomical arrangement of the kidney microcirculation influences
nephron function.
Contrast the physiological significance of blood flow through the renal cortex versus the medulla.
Cortex
- contains renal corpuscle, coiled blood vessels, coiled tubules
- arrangements: tubules and vessels intertwined randomly spaghetti
Medulla
- straight blood vessel and straight tubules
- arrangement: in parallel array like pencils
** kidney microcirculation is a separate network from kidney nephron and collecting duct system (they run parallel)
Filtered Load Equation
Filtered load of X= (plasma concentration of X) x GFR
Urinary excretion equation
Urinary excretion= filtered-reabsorbed-secreted
Tubular reabsorption equation
Tubular reabsorption= GFR- urinary excretion + secreted
How does tubular secretion occur?
excretion > filtration
Urine Excretion rate equation
urinary concentration of X (Ux) x urine flow rate (V)
What is renal clearance?
Volume of plasma completely cleared of a substance by the kidneys per unit time
FLOW RATE/ RATIO
Renal Clearance equation
Cx= (Ux x V)/ Px
Glomerular Filtrate definition
It makes up how much of RBF? normal values>
- volume of plasma/blood filtered through both kidneys per unit of time. (mL/min)
- fluid filtered across glomerular capillaries in Bowman’s space
- ~20% of RBF
- 125ml/min
Filtrate Fraction (definition, equation)
- the fraction RBF that is filtered across glomerulus
FF= GFR/RBF
As FF increases, what happens to oncotic pressure of EFFERENT arteriole? Why?
increases
bc it facilitates reabsorption of tubular fluid (decreased amount of fluid leaving the glomerulus)
What can change FF?
- exm of clinical problems
GFR or RBF
decrease RBF due to hemorrhage or renal artery stenosis
-compensate-> increase GFR to make FF increase
T/F Filtered load is the same as Filtration fraction
FALSE
Filtration Load
-rate in mg/min
Filtration Fraction
-ratio of GFR to RBF
How will changes in filtration, reabsorption, or secretion will affect renal excretion of
each compound? (what are individual equations and what is it combined?)
Filtered load= GFR x Pna+
Reabsorption= filtered load-excretion
Excretion= V x Una
Percentage of filtered load is reabsorbed= reabsorption/ filtered load
Normal GFR= 125ml/min
Inulin Characteristics
- freely filtered
- BUT neither reabsorbed nor secreted
amount excreted (urinary inulin concentration)= amount filtered (plasma inulin concentration)
Creatinine Clearance
- freely filtered
- Metabolism of creatine phosphate in muscle
- unlike inulin, a small amount is secreted
- used to measure GFR but not an ideal marker
