Renal I Flashcards
Functional Unit of the kidney
Nephron
The nephron does the work of making urine to remove waste and reabsorbing electrolytes to maintain the what?
ECF
Extra Cellular Fluid
Loss of how many nephrons pushes you towards kidney failure/uremia?
> 50%
Loss of nephrons makes it more difficult to filter the blood
Age of 40 does what with nephrons?
Decrease about 10% per decade or 1% per year
Age of 80 does what with nephrons?
-40%; 480K-720K
Net function of glomerulus?
Filters and hold capillary beds
Net function of proximal tubule?
Reabsorbs salts and drug secretion
New functions of descending LOH?
Loop of Henle
Reabsorbs water
What are the mid to late parts of the nephron?
- Ascending loop of henle
- Distal convoluted tubule
- Collecting duct
Net functions of ascending LOH?
NaCl reabsorption
Net functions of collecting duct?
Adjusting water
Where does ANGII constrict?
Proximal tubule
Reabsorb for NaCl
Aldosterone and ADH effects what?
Collecting duct
Reabsorbs H2O and Urea
Drug secretion is done by what?
In the proximal tubule
OAT’s and OCT’s
Organic anion/cation transporters
Normal Plasma osmolarity
300 mOsm
The size of kidneys is only how much of the body mass?
0.5%
Kidney gets how much of the cardiac output?
20%
Calculation of RBF:
5L/min x 20% = 1L/min
Name the 9 steps of blood flow through kidney:
AIA-GEP-VIA
Arcuate artery
Interlobular artery
Afferent arteriole
Glomerulus
Efferent arteriole
Peritubular capillaries
Vasa recta
Interlobular vein
Arcuate vein
Why does such a small organ get such a large amount of blood flow?
For the process of filtration because ischemia causes problems in nephron
Where is there high pressure in the nephron and what is the function of that?
In the afferent arterial to the glomerulus
For filtration
What does the high pressure look like with hydrostatic and oncotic pressure?
Hydrostatic > oncotic
Pushes out to get filtered
Refresher: Hydrostatic pressure does what?
Pushes fluid out
Refresher: Onconic pressure does what?
Pulls fluid in
Where is there low pressure in the nephron and what is the function of that?
Efferent arterial and peritubular capillaries
Reabsorption of fluid
What does the low pressure look like with hydrostatic and oncotic pressure?
Oncotic > hydrostatic
Pulls fluid in to reabsorb
What does the vasa recta provide pressure wise?
Low pressure osmotic counter current
What is counter current flow?
In countercurrent flow, the two flows move in opposite directions.
Two tubes have a liquid flowing in opposite directions, transferring a property from one tube to the other. For example, this could be transferring the concentration of a dissolved solute from a high concentration flow of liquid to a low concentration flow.
Filtered load equation?
Plasma [x] x GFR
What does the filtered load equation tell you?
How much is actually filtered
What is the 3 layer barrier in the glomerulus that helps promote filtration and limit what is able to cross into the nephron?
- Fenestrated capillary endothelium
- Glomerular basement membrane
- Podocytes with filtration slits
What 3 things determine what crosses the membrane?
- Glomerular filtration membrane
- Size and charge of filtered molecules
- Net filtration pressure
What charge is the glomerular basement membrane?
Negative
When sizes are equal, what charge has a harder time being filtered?
Negative charged substances
When sizes are equal, which charge substances are easily filtered?
Positively charged substances
From easiest to hardest what is filterable: inulin, glucose, albumin, water, sodium, myoglobin, urea, hemoglobin
Urea, glucose, sodium, water, inulin, electrolyes
Myoglobin
Hemoglobin
Albumin
What is the major driving force of filtration?
High P GC (glomerular capillary hydrostatic pressure)
Net filtration pressure (NFP) equation?
Normal Values for NFP
(50-10)-(25-0)= 40-25= +15mmHg (positive = out pressure)
Why is there no Bowman’s capsule colloid osmotic pressure?
Shouldn’t filter proteins because they don’t make it into the capsule
If you increase P GC then what happens to the filtration?
Increase
What 2 factors do GFR come down to?
- Permeability glomerular capillary
- Net filtration pressure (starling forces)
Rate at which filtrate is formed by both kidneys per minute
Glomerular filtration rate (GFR)
What is the key measure of renal health?
GFR
GFR is passive process that is driven largely by what?
NFP (particularly high P GC)
NFP: Net filtration pressure
What is the only thing that the glomerulus can not filter from plasma?
Proteins
Is it practical to measure GFR by Kf or NFP?
No
What represents how much of a substance can be removed from a certain amount of plasma volume in a given amount of time?
Clearance
Think volume of fluid = clearance. Not how much of the substance was removed.
We can use clearance to estimate what?
GFR
Clearance equation:
(U x UV) / P
Unit: mL/min
U= solute in urine
UV= volume of urine
P= solute in arterial plasma
What is the gold standard to find renal clearance?
Inulin
What are the 4 reasons why inulin is ideal for renal clearance?
- Non-toxic and infusible
- Freely filterable by the kidney
- Not reabsorbed, secreted, metabolized, synthesized or stored in any way
- Unable to alter GFR
Clearance of inulin is equal to what?
GFR
What are the 4 steps to use inulin in renal clearance?
- Infuse a substance into the pt
- Achieve steady plasma conc
- Collect urine and blood
- Calculate clearance
What is the second best way to calculate renal clearance?
Creatinine
What are the 5 reasons why creatinine is used for renal clearance?
- It’s a metabolite produced by creatinine phosphate metabolism (no infusion needed)
- In normal healthy person the rate of production is constant (rate of production=rate of excretion)
- Freely filterable by the kidney
- Not reabsorbed
- Small secretion into the nephron (~10%)
What are the 3 steps to use creatinine for renal clearance?
- Collect blood
- Measure creatinine
- Use prediction equation
How is plasma Cr related to GFR?
Inversely
Doubling plasma Cr represent what with GFR?
Large reductions
A 50% reduction in GFR from 125 to 62.5 induces what to plasma Cr?
100% increase from 1 to 2
Does GFR decline naturally with aging?
Yes
Stage 1 CKD; kidney damage with normal GFR
> 90 GFR
Stage 2 CKD; kidney damage with mild GFR
60-89 GFR
Stage 3A CKD; mild to moderate GFR
45-59 GFR
Stage 3B CKD; moderate GFR
30-45 GFR
Stage 4 CKD; severe GFR
15-30 GFR
Stage 5 CKD; kidney failure
<15 or dialysis GFR
What is the normal value of GFR?
125
GFR of both kidney in ml/min and L/day?
125 ml/min
180 L/day
bout how much of volume filtered (GFR) is reabsorbed?
~99%
What is the normal plasma volume (PV)
3L = filtered 60 x’s/day
What is the calculation for RBF:
5-6L x 20% = 1000-1200ml/min
How much RBF goes through the kidney when comparing body weight?
3.5mL/min/g (<0.5% Bodyweight)
What is the % plasma filtered into the renal tubules?
Filtration fraction (FF)
What is the FF equation?
GFR/ renal plasma flow (RPF)
What is the FF:
125mL / 600mL/min=20%
What is the normal renal plasma flow?
600 mL/min
Is O2 a critical factor for regulating RBF?
No
Is high RBF for filtration or metabolism?
Filtration, not metabolism
If we constrict only the AA what would happen to RBF, PGC, GFR?
Everything decreases
If we constrict only EA, what would happened to RBF, PGC, and GFR?
- Decrease RBF
- Increase PGC
- Maintain GFR
What does the kidney use to protect RBF and GFR from changes in MAP?
Neuroendocrine regulation and intrinsic autoregulation
What is the normal MAP for kidney?
80-180mmHg
What is neuroendocrine regulation?
Vasoconstrictors vs dilators
Can be impaired during disease (HTN)
Neuroendocrine influences what?
RBF
What does NE/Epi do to the RBF?
Decrease
Constrict
Pain, stress, exercise, hemorrhage deals with what agent?
NE/Epi
Primary affect of ANGII and ADH/AVP and where?
Constrictor on EA
What does ANGII and ADH/AVP do to RBF?
Decrease
Countered in AA via NO and PG is affected with what agent?
ANGII and ADH/AVP
Adenosine (ATP) has what primary effect and where?
Constrictor on AA
What does adenosine (ATP) cause in RBF?
Decrease
Released of macula densa during increase tubular flow deals with what agent?
Adenosine (ATP)
NO primary effect and where?
Dilation on AA and EA
What does NO do to RBF?
Increase
Sheer stress; helps keep GFR constant despite constrictors deals with what agent?
NO
Renal prostaglandins primary effect and where?
Dilation on AA
What does renal prostaglandins do to RBF?
Increase
Helps keep GFR constant depsite constrictors deals with what agent?
Renal prostaglandins
ANP primary affect and where?
Dilation on AA
Constriction on EA
High atrial pressure deals with what agent?
Dilation of ANP
Dopamine primary effect and where?
Dilation on AA and EA
Dopamine causes what with RBF?
Increase
Stretching the vascular wall of blood vessel will have a reflexive contraction explains what?
Myotonic mechanism
The reflexive contraction in myogenic mechanism is a what property?
Intrinsic property of smooth muscle
Each nephrons distal tubules (downstream), can communicate with the arterials of the glomerulus (upstream) to alter GFR explains what?
Tubuloglomerular feedback (TGF)
When Na in distal tubules is high, what happens with the GFR?
Lower
When Na in distal tubules is low, what happens to GFR?
Rises
Tubuloglomerular feedback helps keep what in nephron constant, which helps maintain ECFV?
GFR and Na
Renal triad of AKI is:
Acute Kidney Injury
Decrease in GFR
Decrease in urine output
Increase in BUN
What is the first step of urine production?
Filtration
Sevoflurance represents a theoretical risk for what?
AKI
