Katz: Renal Basics Flashcards
What is renal function good for?
- Homeostasis (keeping water and solutes balanced)
- Waste productds (Creatinine, NH4, Urea)
- Regulation of MAP
- H+ Acid Base Balance
- Endocrine Organ
What hormones is the kidney responsible for?
- EPO> RBC > hematocrit
- Active Vit D (hydroxylated in the kidney)
- Renin > ang I > ang II
What does the triple filtration barrier between the glomerular capillary lumen and bowman’s space consist of?
- Capillary endothelium (10% SA has fenestrations)
- GBM (sieve)
- Podocytes (filtration slits)
How does diabetic neuropathy lead to a loss of glomerular filtration?
DN causes glomerulosclerosis (collapse of the glomerular capillaries). About HALF of the dialysis pop has diabetes.
How does Good Pasture Syndrome affect the kidneys?
Autoantibodies target the GBM
What causes alport syndrome?
Mutations in the GBM
What is minimal change disease?
Podocyte foot processes are partially fused (diffuse retraction and effacement of the foot processes) >
loss of albumin in the urine
What is GFR?
The combined rate of fluid movement from glomerular capillary lumen to bowman’s space for all nephrons in both kidneys
What is the equation for GFR?
kf= openness of hte glumerular capillary pores
GFR= kf [( Pgc+ Obs) - (Pbs + Ogc)]
What is the relationship between the concentration of albumin and the plasma protein osmotic pressure Oc?
Only a tiny amt of albumin is filtered and 90% of the filtered albumin is reabsorbed back into the blood leading to the plasma protein osmotic pressure.
What is microalbuminuria?
AER (albumin excretion rate) > 30 mg/day
Can be indicative of glomerular disease
An AER >3000mg/day is indicatve of what?
Nephrotic syndrome–these people can have a LOW plasma albumin
Why is their enormous filtration across the glomerular capillaries?
B/c the kidneys receive about 1/5 of cardiac output
How much blood do the kidneys receive? How much plasma do they recieve?
Both kidneys receive about 1000 ml/min of blood.
If the hematocrit is 40%, then both kidneys combined receive 600 ml of plasma.
What generally is the RPF (renal plasma flow)?
600 mL/min
How much blood is filtered at the glomerular capillaries?
125 ml/min (GFR)
What happens to the remain 475 ml/min that doesn’t get filtered through the glomerular capillaries?
It leaves the kidney via the efferent arteriole
What is the filtration fraction?
The fraction of the renal plasma flow that is filtered.
What is the equation for filtration fraction?
GFR/RPF (125/600=.2)
Only about 20% of RPF gets filtered.
What does NE do to the kidney?
Constricts the AFF and EFF arteriole
What does Ang II do to the kidney?
only EFF constriction
What does hte blood leaving the glomeruli through the efferent arteriole have a HIGH hematocrit and HIGH oncotic pressure?
There is a decreased concentration of water (b/c it has been filtered) resulting in increased water and increased albumin.
How do the concentrations of Na differ in the aff and eff arterioles?
They are equal (both 140)
What is the lumen of the proximal tubule lined with?
renal tubular epithelial cells
What happens to GFR as you get older?
FALLS with increased age and weight
What happens to Pgc, RPF and GFR when there is vasoconstriction of the aff arteriole?
All three are decreased
What happens to Pgc, RPF and GFR when there is vasoconstriction of the eff arteriole (angio II)?
Pgc increases
RPF decreases
GFR increases or stays the same
What’s more important in determining GFR, RPF or Pgc?
Pgc
What happens when there is stimultaneous afferent/efferent arteriole vasoconstriction?
Pgc stays the same
RPF decreases
GFR stays the same or decreases
Can the kidneys control Pgc and GFR somewhat independently of RPF?
Yes
What is the filtered load of solute equal to?
GFR x (free plasma concentration of solute)
What are the filtered loads of glucose and Na?
25,000 mM Na/day
900 mM glucose/day
Seemingly WAY to high
What is the excretion rate of a solute?
Urine flow rate x (urinary concentration of a solute)
The excretion rate of water and solutes is just enough to stay in balance.
What is one of the only solutes whose filtered load is equal to the excretion rate? What does this mean?
Creatinine
There is no resabsorption, secretion, production or destruction of these solutes by the nephron.
What is the equation for GFR?
GFR= (UFR x [Cru] / [Cr}p
Excretion of special solutes (creatinine)/ special solute plasma concentration
What happens to creatinine clearance as GFR falls?
creatinine clearance falls
What is a good marker for GFR?
creatinine
What happens to creatinine if GFR falls by 1/2?
Plasma creatinine will increase by a factor of 2
What is the equation for creatinine production rate?
GFR x (creatinine in plasma)
What is indicated by an increased BUN (plasma urea) in addition to a plasma creatinine?
GFR is almost certainly reduced
What may be the best indication of reduced GFR?
Plasma cystatin C (endogenous protease inhibitor)
What three products are affected by GFR?
Creatinine, cystatine C and BUN can only exit the body via GFR so if GFR falls their respective plasma concentrations increase
