Elements of Renal Function Flashcards
what are some waste products that the kidneys remove
urea, creatinine, acid, bilirubin, other stuff
where is EPO made
kidneys
what is EPO made in response to
low PO2
what causes drops in PO2
anemia caused by blood loss, arterial hypoxia, inadequate renal flow
what is calcitriol and where is it made
active Vit D; kidneys
where does gluconeogenesis occur
mostly liver but a substantial amount can happen in kidneys
the cortex contains what
renal corpuscles, coiled blood vessels, and coiled tubules
the medulla contains
straight blood vessels and straight tubules
the microcirculation of the kidneys is comprised of how many capillary networks and how are they arranged
2; in series
what are the capillaries of the kidney
glomerular and peritubular
what does the glomerular capsule prefer
filtration
what does the peritubular capillary prefer
absorption
what are the Pc of the glomerular and peritubular capillaries
~60 mm Hg; ~13 mm Hg
long medullary peritubular capillaries are often called
vasa recta
where is renal blood flow highest
cortex then outer medulla then inner medulla
when do we start losing nephrons
10% each decade beyond 40
what is the main process of the glomerulus
filtration via starling forces
what is the main process of the proximal tubule
reabsorption of the largest fraction of glomerular filtrate
what is the main process of the loop of henle
controlling urine concentration and secreting Tamm-Horsfall glycoproteins
what is the main process of the distal tubule/collecting ducts
fine control of salt and water secretion
How do you calculate renal clearance C_x
C_x=Urine concentration of X * urine volume/ concentration of X in plasma
How do you calculate glomerular flow rate
GFR = urine concentration of inulin*urine volume/plasma concentration of inulin
How do calculate clearance ratio
Clearance of X / clearance of inulin
How do you calculate renal plasma flow
RPF = (urine concentration of PAH * urine volume)/ (renal artery PAH concentration - renal vein concentration of PAH)
What is the issue with effective renal plasma flow
Underestimates RPF by 10%
What is effective renal plasma flow also equal to
Clearance of PAH
How do you calculate the Glomerular Filtration Rate
GFR = urine concentration of inulin * urine volume / plasma concentration of inulin
What does glomerular filtration rate also equal
Clearance of inulin
How do you calculate filtration fraction
FF - GFR / RPF
How do you calculate filtered load
Filtered load = GFR * plasma concentration of X
How do you calculate excretion rate
Excretion = urine volume * urine concentration of x
How do you calculate reabsorption or secretion rate
Filtered load - excretion
If > 0 then net reabsorption
If < 0 then net secretion
What are the 3 ways that sympathetic can increase BP
- α1 activation with more constriction on afferent arterioeles
- Stimulating juxtaglomerular cells to release renin through β1 receptors
- Na-K ATPase incereasing reabsorption of Na from α1 activation on tubular epithelial cells
How do you calclulate urinary excretion
Urinary excretion = amount filtered - amount reabsorbed + amount secreted
How do you calculate tubular reabsorption
Tubular reabsorption = glomerular filtration - urinary excretion + amount secreted
If excretion > filtration then what has happened
Tubular excretion
How do you calculate V
Urine volume/time
Generally in mL/min
What is renal clearance
The rate at which substances are removed from plasma
It is measure as the volume of plasma cleared of a substance by the kidneys per unit of time
Clearance is a ___________ rate
Flow
What is the glomerular filtrate
Volume of plasma filtered into the combined nephrons of both kidneys per unit time
Also the fluid that goes into Bowman’s space
When would we expect protein and cells in glomerular filtrate
In the event of damage
How do you calculate filtration fraction
GFR/RPF
What does Kf depend on
Permeability and surface area
What is the main influence of filtration fraction
Influenced by blood pressure
How does the filtration fraction relate to the oncotic pressure in the peritubular capillaries
As it increases there is less water in the capillaries so the oncotic pressure increases
How does renal artery stenosis or severe hemorrhage affect FF
Decreased RBF so GFR must increase to maintain homeostasis
GFR/RBF where GFR goes up and RBF goes down
What is the difference between filtered load and filtration fraction
Filtered load is the amount of substance in the blood filtered in unit time
Filtration fraction relates to blood flow
How do you calculate filtered load
GFR X PNa
What is normal GFR
125 mL/min
When can renal clearance be used to estimate GFR
- Substance can be freely filtered
- Substance can’t go out of or into the tubules
- Can’t be synthesized, metabolized, or accumulated in the kidney
- Physiologically inert
What do we normally use to look at GFR
Inulin or creatinine
What is the issue with using inulin
We have to infuse it
Why do we normally use creatinine clearance for GFR
Body makes it naturally and production = excretion
What is an issue with creatinine and GFR
Some (10%) is secreted in the tubules
What is the relationship between plasma creatinine concentration and GFR
Inversely proportional
What do we use to isolate renal issue location
BUN/creatinine
How do we determine pre-renal, post-renal, or intrarenal diseases
> 20:1
10-20:1
<10:1
What are some pre-renal diseases
Hypovolemia, dehydration, reduced renal perfusion, and high protein
What are post-renal issues
Ureter backup
What are some intrarenal issues
Liver disease and low protein diet
The normal formula over/under-estimates creatinine clearance
Over
What is used to estimate renal plasma flow
PAH
Where is most PAH filtered out of the blood
Peritubular capillary which is why it is used to estimate RBF
