Renal Basics Flashcards
What is Homeostasis?
Property of a system that is regulated so internal conditions are stable and relatively constant!
What are the nine main fxns of the Kidney?
- Filtration (Clearance of Na+, drugs, creatinine, Urea, H+)
- Maintaining blood pressure
- Na+ homeostasis (volume)
- H2O homeostasis
- K+ homeostasis
- Bone/mineral homeostasis (VitaD, PO4-)
- Acid-Base homeostasis
- RBC production & regulation (EPO = erythropoietin)
- Gluconeogenesis (kidney is also an endocrine organ)
What can the kidney sense very small changes in?
Oxygen levels!
How many glomeruli do premees have? What does some evidence suggest?
-Fewer glomeruli than normal baby (
How much of the cardiac output goes through the kidney on first pass?
20%! (~1000 ml/min blood)
What other structures have more blood flow per gram weight than kidney?
Brain (maybe liver)
What is the blood composed of?
40% RBC
60% Plasma
What does protein in the urine indicate?
KIDNEY DAMAGE
What is the Renal Plasma Flow (RPF)?
600 ml/min
What are two mechanisms by which the glomerulus restricts what it filters?
- Size
2. Charge
What three components of the glomerulus helps restrict filtering by size?
- Capillary Endothelium
- Basement Membrane
- Podocytes
How does the Capillary Endothelium restrict filtering?
- It’s 10% pores & fenestrations
- -> Anything but cells & protein go through
How does the Basement Membrane restrict filtering?
It’s ANIONIC (negative charge)
- Anionic component = heparin sulfate proteoglycan
- Type IV collagen network - like a sponge!
How do Podocytes restrict filtering?
These are cells exterior to the basement membrane forming small, negatively charged slits.
-Can form slit diaphragms that block the absorption of large molecules!
What sizes and molecules are freely filtered?
Anything
What is normally NOT filtered?
Anything > 70,000 D
How big is albumin?
66,000 D –> some but very little can get through the glomerulus
How does charge prevent filtration in the glomerulus?
GMB & Slit diaphragms are negatively charged; hence, anionic particles filter less well than cationic!
What is the definition of GFR?
Glomerular filtration rate.
-Movement of fluid and solute across from the capillary lumen into Bowman’s space across all glomeruli in both kidneys
What does a reduced GFR indicate?
Tells us the kidney’s ability to filter is reduced/subpar/below where it should be
Why does pi*bs = 0 most of the time?
There is NO ONCOTIC pressure in the Bowman’s space!
What is the normal GFR?
180L/day
What is the renal plasma flow (RPF) into the glomerulus and out of?
600 ml/min in
475 ml/min out
How much does the glomerulus filter out per day?
2L/day
What does NE do the afferent and efferent arterioles of glomerulus?
Vasoconstricts
What does Angiotensin II do the afferent and efferent arterioles of glomerulus?
Vasoconstricts
-More influence on the efferent arteriole
What do PGE (prostaglandins) do the afferent and efferent arterioles of glomerulus?
Vasodilates!
What is the mechanism of Tordol?
Inhibits prostaglandins, causing vasoconstriction of glomerular capillaries
What is the mechnaism of ACE inhibitors?
Inhibit Angiotensin II, causing vasodilation of glomerular capillaries
What happens to RPF and GFR when you Vasoconstrict the afferent arteriole of glomerulus?
GFR decreases.
RPF decreases.
Pressure in glomerular capillaries decreases.
What happens to RPF and GFR when you Vasodilate the afferent arteriole of glomerulus?
GFR increases.
RPF increases.
Pressure in glomerular capillaries increases.
What happens to RPF and GFR when you Vasoconstrict the efferent arteriole of glomerulus?
GFR stays the same or increases.
RPF decreases.
Pressure in glomerular capillary increases.
What happens to RPF and GFR when you Vasodilate the efferent arteriole of glomerulus?
GFR decreases.
Pressure in glomerular capillary decreases.
RPF likely decreases.
What is the filtration fraction?
Percentage of renal plasma flow that is freely filtered.
20%!! (Na+, Cl-, Bicarb., etc.)
How do you calculate the filtered load?
[Xserum]*GFR
-Different for every ion/thing!
Sodium = 140 mEq/L x 180 L/day = 25,000 mEq Na+/day
How do you calculate the excretion rate?
[Xurine]*UFR
- Should always be what is necessary to keep you in balance!
2. 5 L/day * 200 mM/day = ~4.5 grams Na+
What does glucose in the urine indicate?
- You’ve damaged the tubule.
2. You’ve exceeded the amount of glucose you can absorb.
What happened to the RPF and GFR in the old lady on NSAIDS and ACE inhibitors?
- NSAIDS –> inhibit PGE and cause vasoconstriction of the efferent arteriole.
- ACEi —> Inhibit Angiotensin II and cause vasodilation of the afferent arteriole.
- These two combined cause Decreased RPF, Decreased GFR and decreased Pressure in the glomerular capillary.
What are some examples of special circumstances where the Filtered Load (FL) = Excretion Rate (ER)?
Solute is completely filtered (no reabsorption).
Creatinin, Inulin, Iohexol
What is the equation for GFR?
([X]urine * UFR) / [X]serum = ERsolute/Plasma conc. of solute
What are the two ways you can use Creatinine to estimate kidney function?
- Measure CrCl directly
2. Estimate CrCl
How do you measure Creatinine Clearance directly?
CrCl = measurement of a 24 hr urine.
- It assumes a steady state
- Only used in very specific clinical circumstances
- Good test, but rarely collected appropriately
- Need to order a urine creatinine to determine if it was collected appropriately
How much Creatinine should someone produce in a day?
1,440 mg/day = ER = UFR*[X]urine
What is the normal Creatinine production for a male and female?
~25 mg/kg/day = male
~20 mg/kg/day = female
What two equations are not valid if renal function is near normal?
- Cockcroft-Gault
2. MDRD (designed from modification of diet in renal disease study)
How can you estimate CrCl?
Cockcroft-Gault Equation:
[(140-age) (wt in kg) (.82 if female)] /72*Serum Cr
How can you estimate GFR?
Use MDRD!
GFR = 186.3 x Serum Cr (exp[-1.154]) x Age(exp[-0.203]) * (0.742 if female) * (1.21 if black)
What problems are associated with using Creatinine as an estimator?
Creatinine will be secreted at a variable amount depending on renal function!
-10-40% is secreted
-Secretion will ramp up in early phases of GFR decline
[General rule of renal fxn falling by 1/2, Creatinine doubles, doesn’t work in early phases]
