13. Renal Function Flashcards
Label A-D
A: capsule (CT)
B: cortex
C: medullary pyramids
D: ureter
Label A-C
A: arcuate vessels
B: interlobular arteries
C: interlobar vessels
What is the path of renal arteries?
What are the 2 secondary capillary plexi providing blood to the kidney paryenchyma?
Renal artery -> interlobar vessels -> arcuate arteries -> terminate in glomeruli in BC. Plasma filters from glomerular capillaries into space of capsule.
1. vasa recta -> to medulla and loops back on itself, provides blood and helps generate high osmotic ressure in medulla
2. cortical capillary network - allow material exchange between blood and cortical tubules
Label A-H
A: afferent arteriole
B: DCT
C: macula densa
D: juxtaglomerular cell
E: efferent arteriole
F: bowman’s capsule
G: glomerulus
H: PCT
What is the filtration fraction of blood plasma filtered through glomerulus?
What is the path?
What is the difference between the afferent and efferent arterioles, and what does this create?
20%
glomerulus -> capsular space -> PCT
Afferent = larger diameter so pressure decreases between afferent and efferent. Creates filtration pressure forcing fluid through capillary endothelium -> capsular space.
Describe glomerular capillaries.
What is proteinuria?
Fenestrated and covered on outside with extra layer of podocytes which have slits between them (filtration mechanism).
Renal disease: slits become inflamed and enlarged enabling more solutes to enter urine - mainly proteins = proteinuria
Label A-D
A: podocyte cell body
B: fenestrations
C: foot processes of podocytes
D: filtration slits
E: cytoplasmic extensions of podocytes
What is the path of fluid from the afferent arteriole?
What is the formula for excretion from the kidney?
What is the average net filtration pressure?
Glomerulus -> PCT -> LoH (in medulla) -> DCT -> CD -> ureter (all = NEPHRON)
Excretion = filtration - reabsorption + secretion (in PCT, reabsortion and secretion to/from peritubular capillaries)
10mmHg
1.2L/min
What is the average kidney outflow and glomerular filtration rate?
What is average renal plasma flow and urine flow?
How much filtered fluid is reabsorbed, and where is most of it reabsorbed?
1.2L/min and 120-125ml/min
680ml/min and 1ml/min
99%, 2/3 in PCT
Describe how fluid is reabsorbed in the PCT
Na+ pumps in basal membrane move Na+ -> interstitial fluid. Na+ channels in luminal membrane so Na+ passes lumen -> cells down its conc gradient, carries glucose with it.
H2O reabsorbed down osmotic gradient, lumen -> cells -> intersitiual fluid.
What is glomerular filtration rate (GFR) for both kidneys and how is it measured?
What happens to clearance if substance in blood is:
a) not removed at all by kidney
b) removed at same rate as H2O passes through glomeruli
c) completely removed from the blood passing through the kidney
Effective volume of plasma completely ‘cleared’ of a substance/min (usually 120-125ml/min), measured by clearance of a selected material in L/min.
a) clearance = 0
b) clearance = GFR
c) clearance = RPF (renal plasma flow)
How does kidney damage affect GFR and RPF?
GFR is an important test of kidney health. What is the formula for clearance?
Normally GFR decreases but RPF may be normal.
Clearance = ([U]/[P]) x [V]
where U = urine conc, P = plasma conc and V = urine vol/min
What is the gold standard for measuring GFR and why is it not used much?
What is used clinically to measure GFR, and why is this an overestimate?
What are normal creatinine clearance levels for a male and female?
Inulin Clearance: Completely filtered from blood plasma. But need inulin IV over hours to get stready plasma conc.
Creatinine used clinically - break down prod of creatine phosphate in muscle, freely filtered by glomerulus. Creatinine normally already at steady state conc in blood so easier to measure than inulin.
It is also actively secreted by peritubular capillaries in small amounts - this secretion means creatinine clearance overestimates actual GFR by 10-20%.
NB: normally 24 hr urine collection and blood test for creatinine
Male: 88-128ml/min Female: 97-137ml/min
Apart from GFR, what can creatinine clearance also be used to measure?
What is the substance used to measure clearance and hence RPF?
RPF - if substance in blood completely removed from blood passing through kidney, clearance - RPF.
PAH (para-amino-hippuric acid). Infused until steady blood conc measured and urine collected for 24hrs.
GFR is autoregulared - what does this mean, and thus what can be measured?
Hence what kinds of releasing cells are found in the kidney?
It (and RPF) doesn’t change over a wide range of BPs, thus pO2 in interstitium - measure of O2 carrying capacity of blood.
Erythropoietin