Unit 4: Renal Physiology Pt3--Kidneys Flashcards
What is the measure of renal function?
Glomerular Filtration rate (GFR)
What is the GFR equal to the clearance of?
- inulin
- serum creatinine
- blood urea nitrogen (BUN)
What is the normal GFR?
What must it be at to be considered Kidney (renal) Failure?
greater than 90 ml/min
GFR less than 15 ml/min
What does Renal Clearance describe?
rate at which substance are removed from the plasma
volume of plasma completely cleared of a substance by the kidneys per unit of time
What is the equation for Clearance of the kidney?
Clearance = (urine conc. of substance X) / (plasma conc. of substance X) x urine flow rate
What can urine flow rate vary from?
0 to 600 mL/min
if at 0 it means NOT cleared
What is the renal clearance proportional to? What is it inversely proportional to?
proportional–> to urine conc of susbtance X ( increase urine conc. of substance X; will increase clearance)
inversely proportional to –> plasma conc. of substance X
What three pieces of information do we need in order to calculate renal clearance?
- urine conc. of substance X (mg/mL)
- plasma conc. of substance X (mg/mL)
- urine flow rate (mL/min)
What does the clearance of inulin equal to? How is this possible?
equal to GFR rate
it is a fructose polymer and is FREELY filtered–> is not reabsorbed or secreted
What has the highest clearances through the kidneys? What is it equal to?
PAH (para-aminohippuric acid)
organic acid that is BOTH filtered and secreted
clearance of PAH = effective renal plasma flow
What can be used to estimate GFR in clinical practice? Why is it only an estimate?
Creatinine –> not perfect substance, b/c some creatinine is secreted by proximal tubule
10% error– which is cancelled by method that overestimates plasma creatine by 10%
What is the equation for Clearance Ratios?
= Clearance of X / Clearance of inulin
What does it mean if the Clearance ratio equals 1?
the clearance of x = clearance of inulin
therefore = GFR
What does it mean if the Clearance Ratio is greater than 1? What is an example of this?
the clearance of x > clearance of inulin
therefore substance x is BOTH filtered and secreted
Ex: PAH
What does it mean if the Clearance Ratio is less than 1? What are examples?
the clearance of x < clearance of inulin
Two Possibilities:
- Substance x is not filtered (Ex: albumen)
- Substance x is filtered and subsequently reabsorbed (Ex: glucose)
What fraction of resting CO do the kidneys receive?
1/4 of resting CO
= 125 ml/min
(180 L/day)
What are the four ways Regulation of Renal Blood Flow (RBF) occurs?
- SNS and circulating catecholamines
- Angiotensin II
- Prostaglandins (PGE2 and PG12)
- Dopamine
What are the afferent and efferent arterioles innervated by? Which one has more alpha1 receptors? What will stimulation do?
both innervated by SNS
Afferent Arterioles have more alpha1 receptors–> SNS stimulation will decrease GFR and RBF
What effect does stimulation of SNS have on kidneys?
decrease GFR and RBF
stimulate release or renin from juxtaglomerular cells
What type of cells is renin released from?
juxtaglomerular cells
What is a potent vasoconstrictor of BOTH Afferent Arterioles and Efferent Arterioles in the kidney?
Angiotensin II
Are Afferent Arterioles or Efferent Arterioles more sensitive to Angiotensin II? What effect will low and high levels of Angiotensin II have?
Efferent arterioles are more sensitive
Low Levels–> increase GFR by constricting Efferent Arterioles
High Levels–> decrease GFR by constricting BOTH Afferent and Efferent Arterioles
overall will decrease RBF
What is produced locally that will vasodilate both Afferent and Efferent Arterioles?
Prostaglandins
What activates Prostaglandins? Why?
activated by hemorrhage (will vasodilate AA and EE)–> to attenuate(reduce effect of) constrictor effects of angiotensin II and SNS to prevent renal failure
What will inhibit Prostaglandin synthesis and what effect can this have?
NSAIDs (non steroidal anti-inflammatory drugs)–> can interfere w/ protective effects of PGs on renal function following hemorrhage
OH NO!
Where is dopamine produced in the kidneys?
produced by Proximal Tubule
What effect will low levels of Dopamine have on different arterioles in the body?
- dilates renal arterioles and cerebral, cardiac, splanchnic arterioles
- constricts skeletal muscle and cutaneous arterioles
What effect will dopamine have on the kidneys?
- dilate arterioles and therefore increase RBF
- inhibits renin secretion (so won’t increase BP and protects brain and heart from high BP)
Will a low or high does of dopamine aid in treatment of hemorrhage?
low does of dopamine–> protective (vasodilatory) effect on brain, heart, and kidney
T/F. RBF and GFR vary easily over a wide range of perfusion pressures
False– they are kept constant over a wide range of perfusion pressures (80-200 mmHg)
How do we accomplish keeping RBF and GFR constant over a wide range of perfusion pressures?
by varying resistance of arterioles –> primarily the afferent arterioles
Where does most autoregulation of RBF and GFR take place?
in the afferent arterioles
What two Hypothesis are there for autoregulation of the kidney?
- Myogenic Hypothesis
2. Tubuloglomerular Feedback
What does the Myogenic Hypothesis involve?
increase arterial blood pressure–> stretches blood vessels–> which causes reflex constriction
–> stretch activated Ca++ channels in Afferent Arterioles
What does the Tubuloglomerular Feedback involve?
increase in RBF will increase GFR which is increasing delivery of solute and water to macula densa of Juxaglomerular apparatus (maybe sensing solute?)
this increases resistance of Afferent Arterioles by release of a local constrictor
How is the GFR and the RBF effected by vasoconstriction of the Afferent Arterioles?
What about for the Efferent Arterioles?
AA constriction–> will decrease GFR and decrease RBF
EE constriction–> will increase GFR and decrease RBF
What does Excretion equal?
Excretion = filtration - reabsorption + secretion
How does one Measure the renal plasma flow using the Fick Principle? Is this practical?
RPF = (PAH conc. in urine) / (PAH conc. in Renal Artery) - (PAH conc. in Renal Vein) x urine flow rate
NOT practical to pick up conc. in renal arteries and veins
How does one measure the Effective renal plasma flow?
Effective RPF = clearance of PAH
Effective RPF = (PAH conc. in urine) / (PAH conc. in plasma) x urine flow rate
~w/in 10%
~ PAH in renal vein is nearly 0 (but not )
Once we have RPF, how do we find RBF?
RBF = RPF / (1- Hct)
What are the layers of the Glomerular Capillary?
- Endothelim
- Basement Membrane
- Epithelium
What layer of the Glomerular Capillary has pores where plasma proteins can pass and RBC’s cannot?
Endothelium
What are the 3 layers of the Basement Membrane of the Glomerular capillary?
- lamina rara interna
- lamina densa
- lamina rara extera–> fused with epithelia
What part of the Glomerular filtration prevents plasma protein filtration?*
Basement Membrane
it is the most significant barrier
What layer of the Glomerular capillary has filtration slits called fenestrations?
Epithelium
Does the Glomerular Capillary have a negative or positive charge on it? Why is this important?
Negatively charge glycoproteins–> on endothelium, BM, and epithelium
provides additional layer of protection from larger MW proteins at physiologic pH that carry a net neg. charge
Of the following Dextran’s which is most filterable and which is least filterable?
- Cationic
- Neutral
- Anionic
- Cationic–> MOST filterable (b/c gets attracted)
- neutral
- Anionic–> LEAST filterable (b/c gets repelled)
What is the hydrostatic P in glomerular capillaries? How does this P change along the cap length? How?
= 45 mmHg
NO decrease in P along cap lenght–> due to constriction of Efferent Arterioles–> this keeps pressure high and promotes filtration
What will the Net filtration P at the END of the Glomerular Capillaries equal?
Net filtration P = 0 mm Hg
therefore no filtration occurs normally at end of glomerular capillaries
