Rao: RBF and Glomerular filtration Flashcards
Are there more superficial nephrons or juxtamedullary nephrons?
superficial (85%) compared to juxtamedullary (15%)
How much of the total cardiac output does the kidney receive?
>20%
Describe the vascular progression from Renal artery to Renal vein (i.e. renal artery–>interlobular arteries–>etc.)
Renal a.–>interlobular aa.–>arcuate aa.–>radial aa (interlobular aa?)–>afferent arteriole–>glomerular capilary bed–>efferent arteriole–>peritubular capillary bed–>renal vein
The afferent arteriole forms the _____ capillary bed
glomerular
the efferent arteriole forms the ____ capillary bed
peritubular
The arteriovenous hydrostatic pressure drop in renal vasculature accurs in 2 steps. what are they?
in the afferent arteriole (from 90 to 61 mmHg) and efferent arteriole (from 59 to 25 mmHg)
In renal vasculature, oncotic pressure increases primarily in one part. Where?
Glomerular capillary
What 3 processes are involved in urine formation?
- glomerular filtration
- tubular reabsorption
- tubular secretion
What is the formula for excretion?
excretion = filtration - reabsorption + secretion
What is the GFR for an average person?
130 ml/min or 180 L/day
what is the filtration fraction equal to?
FF = GFR/RPF
where RPF is renal plasma flow
What are the 3 filtration barriers to the GFR?
- capillary endothelium
- Basement membrane
- Epithelium or podocyte monolayer
What factors determine the filterability of solutes?
size and charge
Albumin is small enough to fit through glomerular pores. Does it have high filterability? why or why not?
No. Albumin is highly negatively charged and less than 1% is filtered
What is the GFR equation?
GFR = Kf x Net filtration pressure
where Kf = filtration coefficient
What factors favor filtration? oppose filtration? Net filtration equation?
Favoring filtration:
Glomerular (capillary) hydrostatic pressure
Bowman’s space oncotic pressure
Opposing filtration:
Glomerular (capillary) oncotic pressure
Bowman’s space hydrostatic pressure
Net Filtration = (favoring filtration) - (opposing filtration)
If you INCREASE AFFERENT resistance, what will happen to the GFR? RPF?
GFR: decrease
RPF: decrease
If you DECREASE AFFERENT resistance, what will happen to GFR? RPF?
GFR: increase
RPF: increase
If you INCREASE EFFERENT resistance, what will happen to GFR? RPF?
GFR: increase
RPF: decrease
If you DECREASE EFFERENT resistence, what will happen to GFR? RPF?
GFR: decrease
RPF: increase
With normal plasma flow, the net hydrostatic pressure doesn’t change much from afferent to efferent, but the colloid osmotic pressure increases from afferent to efferent. What happens in the case of slow plasma flow?
You get a much faster increase in colloid osmotic pressure (check out the two figures)
Is the regulation of GFR dependent on systemic influences?
No. Regulation of GFR is not influenced by extrinsic factors (i.e. regulation occurs in an isolated kidney)
Normally, how much volume is reabsorped daily? how much urine is excreted daily?
- 5 L/day reabsorbed
- 5 L/ day excreted as urine (remember GFR is 180 L/day so subtract the amount reabsorbed to get amount excreted as urine)
What are the 2 major theories regarding autoregulation via changing vascular tone?
- Myogenic mechanism
- Tubuloglomerular feedback mechanism
What is the myogenic mechanism?
Direct stimulation of arterolar smooth muscle.
A theory of autoregulation via changing the vascular tone.
What is involved in the tubuloglomerular feedback mechanism? Desribe it.
Juxtaglomerular (JG) complex (macula densa and JG cells)
Changes in NaCl concentrations in tubular fluid leads to changes in the afferent arteriole resistence and therefore GFR
What happens if the macula densa senses increased [NaCl]?
increased afferent arteriolar resistance –> decreased GFR
What happens if the macula densa senses decreased [NaCl]?
decreased afferent arteriolar resistance –> increased GFR
How does chloride concentration in the distal tubule relate to arteriolar resistance when GFR is INCREASED?
increased GFR –> increased chloride in distal tubule –> Na-K-2Cl cotransporter in macula densa cells –> release of ATP or arachidonate metabolites (i.e. Ca2+) –> smooth muscle contraction –> increased arteriolar resistance
How does chloride concentration in the distal tubule relate to arteriolar resistance when GFR is DECREASED?
decreased GFR –> decreased chloride in distal tubule –> MD sends signal to JG cells –> decrease in arteriolar resistance
What happens in terms of the Renin-Angiotensin system if the macula densa senses decreased Cl-?
JG cells secrete renin–>
increased angiotensin I secretion–>
increased angiotensin II–>
increased aldosterone–>
Na+ and H20 retention
How do adrenaline and endothelin-1 affect GFR?
Both lead to constriction of arterioles and decreased GFR
How do nitric oxide (NO) and prostaglandins affect GFR?
Both lead to decreased vascular resistance and increased GFR
What are 2 general ways in which you can get proteinuria?
- barrier breakdown (e.g. a large pore or loss of charge selectivity)
- abnormal circulating protein (e.g. due to break down of tissue or production of abnormal protein by tumor cells)
