Renal Blood Flow/Glomerular Filtration - McCormick

Question 1

How much blood on average is filtered by the kidney? What is the average glomerular filtrate?

Answer 1

1100-1300 filtered/minute

125-130 mL of glomerular filtrate

Question 2

What is the first step in urine formation? How is it like plasma?

Answer 2

Glomerular filtration

Identical to plasma except no proteins or free RBCs

Question 3

What does the total GFR represent?

Answer 3

The sum of the filtration rate in all functioning nephrons and therefore is an index of functioning renal mass
Can be used to evaluate severity and course of renal disease

Question 4

What types of molecules are more restricted in terms of filtration

Answer 4

Large molecules
Anionic molecules (negative) - negative basement membrane repels the negative molecules more. can be an early indication of disease when proteins are getting through into the urine
-even at the same radius, anionic can’t get through

Question 5

3 Layers of the glomerular membrane?

Answer 5

1. Fenestrated capillary epithelium - water
2. Glomerular basement membrane - negative charge
3. Podocyte epithelium - slit pores restrict large molecules

Question 6

What occurs between the podocyte foot processes that prevents large molecules from getting through?

Answer 6

Nephrin molecules in the filtration slit

Question 7

GFR is the product of 3 physical factors

Answer 7

1. Hydraulic conductivity (Lp) of glomerular membrane
2. Surface area
   - - 1 and 2 = the ultrafiltration coefficient Kf
3. Capillary ultrafiltration pressure –> Puf

Question 8

How do you calculate GFR from ultrafiltration pressure and Kf?

Answer 8

GFR = Kf x Puf

Question 9

How do you calculate Puf?

Answer 9

Pgc - (Pbc + pi(gc)
The difference of 3 pressures
Pbc - Bowman's to GC
pi(gc) - Bowman's to GC
Pgc - GC to Bowman's

Question 10

What can alter Kf?

Answer 10

Mesangial cell contraction

Question 11

Pgc is determined by what 3 things?

Answer 11

Renal arterial bp
Afferent a resistance
Efferent a resistance

Question 12

Contraction of mesangial cells does what?

Answer 12

Shortens cpillary loops, lowers Kf and thus lowers GFR

Question 13

Afferent arteriolar constriction leads to?

Answer 13

Greater pressure drop upstream of GC
Pgc falls which lowers GFR
Renal blood flow falls due to > resistance

Question 14

Efferent arteriolar constriction leads to?

Answer 14

Pooling of blood in GC

Increased Pgc increases GFR

Question 15

RBF is determined by what?

Answer 15

The pressure gradient between renal a and renal v divided by the vascular resistance

Question 16

Vascular resistance to renal blood flow (RBF) is primarily determined by?

Answer 16

Afferent and efferent arterioles

Question 17

Angiotensin II?

Answer 17

Promotes efferent arteriolar constriction

Raises bp and stabilizes GFR

Question 18

3 hormones that decrease GFR?

Answer 18

Norepinephrine
Epinephrine
Endothelin

Question 19

Autoregulation

Answer 19

2 arteriolar beds protect glomerulus
Preserves GFR at times of low systemic bp
Tight control - 75-160mmHg

Question 20

2 Mechanisms for autoregulating renal blood flow and GFR?

Answer 20

1. Myogenic

2. Tubuloglomerular feedback

Question 21

Myogenic mechanism of autoregulation

Answer 21

Contraction of vascular smooth m in response to stretch

Prevents an increase in RBF and GRF when BP increases

Question 22

Tubuloglomerular feedback and autoregulation

Answer 22

Autoregulation of GFR by the rate of fluid NaCl delivery to the macula densa
Feeds back to the kidneys to control afferent and efferent resistance

Question 23

What regulates tubuloglomerular feedback?

Answer 23

Juxtaglomerular apparatus

• macula dense cells in DCT
• juxtaglomerular cells in walls of afferent and efferent

Question 24

3 Components of the juxtaglomerular apparatus?

Answer 24

1. Macula densa
2. Extraglomerular mesangial cells
3. Juxtaglomerular (granular) cells

Question 25

Renal prostaglandins are?

Answer 25

Protective vasodilators