Session 2 Renal Physiology Flashcards
find Urine Excretion Rate
Urine Excretion Rate=Ux x V
Ux=urine amount of X/urine Volume of X
V=urine volume/time collected
Example Problem for urine excretion rate
If a patient has a creatinine clearance of 90ml/min, a urine flow rate of 1ml/min, a plasma K concentartion of 4mEq/L, a urine K concentartion of 60mEq/L, what is the approx. K excretion?
Watch units because she wants to make this harder than it has to be
Urinary Concentatration of K=Ux=60mEq/L
Urinary Flow Rate=V=1ml/min
Convert 60mEq/L to mEq/ml and multiply times V
(60mEq/1000ml)x(1ml/min)=0.06mEq/min
How to calculate GFR?
Renal Clearance Equation if using creatinine or inulin
Cx=Ux x V/Px
Uinulin and Pinulin
Example Problem for renal clearance/GFR
Inulin is used in an experiement to measure the glomerular filtration rate. Inulin is infused to achieve a steady state concentration in the plasma of 1.0mg/dl. Urine is collected over a 10 hour period. The total volume of urine is 1.5 L and urinary concetration of inulin is 440mg/dl. What is GFR as determined from inulin clearance?
Watch units because she obviously knows how good we are at math based on the results of Quiz 2 and wants to up the anty
Cx=Ux x V/Px
Uinulin=440mg/L
V=1.5 L over 10 hours=1.5L/600min=.0025L/min
Pinulin=1.0
Cx=440x0.0025/1=1.1dl/min=110ml/min
If filtration fraction increases, do you expect oncotic pressure in the capillaries (Pic) to increase or decreases?
Increase
Filtered Load is not the same as filtered fraction
filtered load is a rate in mg/min
filtered fraction is the ratio of GFR/RBF
Why do we care about starling forces on the efferent arteriole and peritubular capillary?
Starling forces and changes on the capillaries and efferent arteriole effects what passes through the PCT where 90% of reabsorption happens.
The efficacy of reabsorption in the PCT depends on the starling forces at the peritubular caps. and eff. arteriole
What are the intrinsic mechanisms of renal hemodynamics?
What are the extrinsic mechanisms of renal hemodynamics?
Autoregulation (myogenic reflex) and tubuloglomerular feedback
SNS, hormones (RAAS), blood composition
What is the function of the JG apparatus?
macula dense and JG cells sense NaCl in the DCT
signals are sent between the two groups of cells
feeds back and adjusts arteriolar resistance as needed
renin is released as needed
maintains Na delivery to the distal tubule and constant GFR
see Ninja Nerd for details.
What is the effect of increased NaCl delivery to macula densa
- increase delivery of NaCl to macula densa
- Na reabsorbed via NKCC2
- Stimulates ATP/adenosine signaling
- stimulates calcium signaling in sm. m. around aff. arteriole causing vasoconstriction
- this stimulates decrease GFR and decrease in Renin
What is the effect when there is a decrease in NaCl to the macula Densa?
- decreased NaCl delivery to macula densa
- less Na reabsorbed via NKCC2
- Less ATP/adenosine released
- Ca not released to sm. m surrounding afferent arterioles
- aff. arterioles relax
- increases GFR and renin
When NaCl is delivered to the distal tubule, what else happesn?
- decrease in distal solute delivery activates the tubuloglomerular feedback mechansim
- buffering changes to increase GFR and RBF back towards normal
- buffering is done by dilating afferent arteriole (from PGE2 and NO and decreased ATP/adenosine)
- Renin secretion is increased by NaCl delivery as well as by a decrease in renal pressure or increased SNS (from low BV) and makes ang II to constrict eff. arteriole
Vasoconstrictors
Vasodilators
sympathetics (catecholamines)
endothelin
ATP/adenosine
angiotensin II
Prostaglandins
bradykinin
NO
Dopamine
ANP
ACE inhibitor (lowers GFR)
Ang II acts primarily where and does what?
acts on efferent arteriole and rasies GFR during diminished renal perfusion
ACE inhibitors (inhibit this) and lower GFR
Strong SNS stimulation constricts arterioles and decreases what?
GFR/RBF
local sympathetics and catecholamines act on a1 receptors (moreso on afferent than efferent)
Angiotensin II decreases RBF how?
constricts efferent arteriolar vasoconstriction (you get more blood backing up and pushing out through glomerulus but the rest of the kidney gets less blood as a result)
Ang II increases peritubular capillary oncotic pressure and decreases peritubular capillary hydrostatic pressure. Why?
- GFR increases
- more fluid is filtered from glomerular capillary into the tubular system
- less fliuid passes on into the peritubular capillaries
- proteins are more concentrated as a reuslt
- oncotic pressure increases
FF=GFR/RBF thus here FF increases
Afferent arteriole constrictions (plaque in arteriole mimics this) results in what?
decreased GFR, decreased NaCl to macula densa
causes macula densa and JG cells to secrete renin and make Ang. II constricting efferent arteriole
this results in afferent arteriolar dilation mediated by NO
Assume a clinical trial was conducted in which the investigators succeeded in producing approx. step changes in real function parameters with rapid extracellular volume expansion. This produced an increase in solute delivery to the macula densa. Which of the following is most likely to occur as a result of increased solute delivery to the distal convoluted tubule?
Increase in afferent arteriole tone
Someone is in acute renal failure. Their GFR is 30, serum creatinine is 1.9. What will decrease the creatinine in her blood?
dilating the renal afferent arteriole
someone in chronic resistant hypertension is treated with Ca channel antagonist to decrease resistance of the glomerular afferent arterioles. What will also decrease?
renin release
a 34 year old with diarrhea loses ECF volume. stretch receptors sense that he is dehydrated. What is happening?
increase in sympathetic tone
increase in Ang. II
Decrease in ANP
Increase in Plasma oncotic pressure
The dehydrated diarrhea boy is given fluid but he is overhydrated. Now the glomeruloartubular balance mechanisms in the PCT need to help eliminate the fluid. What is happening?
increase in GFR
increase in peritubular capillary hydrostatic pressure
decrease in peritubular capillary oncotic pressure
