Rao: RBF and Glomerular filtration

Question 1

Are there more superficial nephrons or juxtamedullary nephrons?

Answer 1

superficial (85%) compared to juxtamedullary (15%)

Question 2

How much of the total cardiac output does the kidney receive?

Answer 2

>20%

Question 3

Describe the vascular progression from Renal artery to Renal vein (i.e. renal artery–>interlobular arteries–>etc.)

Answer 3

Renal a.–>interlobular aa.–>arcuate aa.–>radial aa (interlobular aa?)–>afferent arteriole–>glomerular capilary bed–>efferent arteriole–>peritubular capillary bed–>renal vein

Question 4

The afferent arteriole forms the _____ capillary bed

Answer 4

glomerular

Question 5

the efferent arteriole forms the ____ capillary bed

Answer 5

peritubular

Question 6

The arteriovenous hydrostatic pressure drop in renal vasculature accurs in 2 steps. what are they?

Answer 6

in the afferent arteriole (from 90 to 61 mmHg) and efferent arteriole (from 59 to 25 mmHg)

Question 7

In renal vasculature, oncotic pressure increases primarily in one part. Where?

Answer 7

Glomerular capillary

Question 8

What 3 processes are involved in urine formation?

Answer 8

1. glomerular filtration
2. tubular reabsorption
3. tubular secretion

Question 9

What is the formula for excretion?

Answer 9

excretion = filtration - reabsorption + secretion

Question 10

What is the GFR for an average person?

Answer 10

130 ml/min or 180 L/day

Question 11

what is the filtration fraction equal to?

Answer 11

FF = GFR/RPF

where RPF is renal plasma flow

Question 12

What are the 3 filtration barriers to the GFR?

Answer 12

1. capillary endothelium
2. Basement membrane
3. Epithelium or podocyte monolayer

Question 13

What factors determine the filterability of solutes?

Answer 13

size and charge

Question 14

Albumin is small enough to fit through glomerular pores. Does it have high filterability? why or why not?

Answer 14

No. Albumin is highly negatively charged and less than 1% is filtered

Question 15

What is the GFR equation?

Answer 15

GFR = Kf x Net filtration pressure

where Kf = filtration coefficient

Question 16

What factors favor filtration? oppose filtration? Net filtration equation?

Answer 16

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)

Question 17

If you INCREASE AFFERENT resistance, what will happen to the GFR? RPF?

Answer 17

GFR: decrease

RPF: decrease

Question 18

If you DECREASE AFFERENT resistance, what will happen to GFR? RPF?

Answer 18

GFR: increase

RPF: increase

Question 19

If you INCREASE EFFERENT resistance, what will happen to GFR? RPF?

Answer 19

GFR: increase

RPF: decrease

Question 20

If you DECREASE EFFERENT resistence, what will happen to GFR? RPF?

Answer 20

GFR: decrease

RPF: increase

Question 21

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?

Answer 21

You get a much faster increase in colloid osmotic pressure (check out the two figures)

Question 22

Is the regulation of GFR dependent on systemic influences?

Answer 22

No. Regulation of GFR is not influenced by extrinsic factors (i.e. regulation occurs in an isolated kidney)

Question 23

Normally, how much volume is reabsorped daily? how much urine is excreted daily?

Answer 23

178. 5 L/day reabsorbed
179. 5 L/ day excreted as urine (remember GFR is 180 L/day so subtract the amount reabsorbed to get amount excreted as urine)

Question 24

What are the 2 major theories regarding autoregulation via changing vascular tone?

Answer 24

1. Myogenic mechanism
2. Tubuloglomerular feedback mechanism

Question 25

What is the myogenic mechanism?

Answer 25

Direct stimulation of arterolar smooth muscle. A theory of autoregulation via changing the vascular tone.

Question 26

What is involved in the tubuloglomerular feedback mechanism? Desribe it.

Answer 26

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

Question 27

What happens if the macula densa senses increased [NaCl]?

Answer 27

increased afferent arteriolar resistance --\> decreased GFR

Question 28

What happens if the macula densa senses decreased [NaCl]?

Answer 28

decreased afferent arteriolar resistance --\> increased GFR

Question 29

How does chloride concentration in the distal tubule relate to arteriolar resistance when GFR is INCREASED?

Answer 29

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

Question 30

How does chloride concentration in the distal tubule relate to arteriolar resistance when GFR is DECREASED?

Answer 30

decreased GFR --\> decreased chloride in distal tubule --\> MD sends signal to JG cells --\> decrease in arteriolar resistance

Question 31

What happens in terms of the Renin-Angiotensin system if the macula densa senses decreased Cl-?

Answer 31

JG cells secrete renin--\> increased angiotensin I secretion--\> increased angiotensin II--\> increased aldosterone--\> Na+ and H20 retention

Question 32

How do adrenaline and endothelin-1 affect GFR?

Answer 32

Both lead to constriction of arterioles and decreased GFR

Question 33

How do nitric oxide (NO) and prostaglandins affect GFR?

Answer 33

Both lead to decreased vascular resistance and increased GFR

Question 34

What are 2 general ways in which you can get proteinuria?

Answer 34

1. barrier breakdown (e.g. a large pore or loss of charge selectivity) 2. abnormal circulating protein (e.g. due to break down of tissue or production of abnormal protein by tumor cells)