Renal 3: Filtration and Blood Flow

Question 1

What can get through the glomerular filtration barrier?

Answer 1

Neutral molecules smaller than 20A are freely filtered
Molecules between 20-42 A are filtered to a varying degree
Cationic molecules
Anionic molecules are hindered due to negatively charged glycoproteins on surface of glomerular filtration barrier

Question 2

The glomerular capillaries have high/low resistance and a net positive/negative charge.

Answer 2

low, negative

Question 3

Glomerular capillaries have a large/small filtration coefficient. How do we calculate it?

Answer 3

large. Kf = PERMEABILITYgc x AREAgc

Question 4

How are filtration and molecular radius related?

Answer 4

higher radius means lower filterability

lower radius means higher filterability

Question 5

How are filtration and ionic charges related?

Answer 5

Anionic: shifts curve down and left. filterability lower at same radius.
Cationic: shifts curve up and right. filterability higher at the same radius.

Question 6

Why aren’t immunoglobulins filtered?

Answer 6

Their molecular radii are greater than 42 angstroms.

Question 7

Why isn’t albumin filtered?

Answer 7

It is a polyanionic protein with a molecular radius of 35 angstroms.

Question 8

How do we calculate net filtration pressure?

Answer 8

Net Ultrafiltration Pressure: Pgc - Pbs - πgc + πbs

Pgc is glomerular capillary hydrostaic pressure
Pbs is Bowman’s space hydrostatic pressure
πgc is glomerular oncotic pressure
πbs is Bowman’s space oncotic pressure

Question 9

As blood moves through the glomerular capillaries what happens to the following?
Pgc
πgc
Pbs
net ultrafiltration pressure

Answer 9

Pgc: small decrease (low resistance capillaries)
πgc: large increase (conc of proteins that do not filter)
Pbs: no change
Net ultrafiltration pressure: decrease

Question 10

How do we calculate glomerular flow?

Answer 10

hydraulic conductance times net pressure gradient.

GFR = Kf * (Pgc - Pbs - πgc + πbs)

Question 11

How does a change in afferent arteriolar resistance affect (glomerular capillary hydrostatic pressure)

Answer 11

Decreased resistance increases Pgc

Increased resistance decreases Pgc

Question 12

How does a change in the efferent arteriolar resistance affect Pgc (glomerular capillary hydrostatic pressure)

Answer 12

Decreased resistance decreases Pgc

Increased resistance increases Pgc

Question 13

How does a chagne in the renal arteriolar pressure affect Pgc(glomerular capillary hydrostatic pressure)?

Answer 13

Increase in BP transietly increases Pgc -> inc GFR

Decrease in BP transiently decreases Pgf -> dec GFR

Question 14

What happens to the following in early stage glomerulonephritis?
πgc
GFR
Pbs

Answer 14

decrease
increase
nothing

Question 15

What happens to the following in late stage glomerulonephritis?
Pbs
GFR

Answer 15

increase

decrease

Question 16

How do kidney stones affect Pbs and GFR?

Answer 16

increases Pbs

decreases GFR

Question 17

What does nephritic syndome do?

Answer 17

increases hydraulic conductance (Kf) and causes proteinuria

Question 18

What is the equation for total renal blood flow (RBF)

Answer 18

RBF = (P renal artery - P renal vein)/R renal vasculature

Question 19

Rank the following from most to least vascularization:
inner medulla
renal cortex
outer medulla

Answer 19

renal cortex&raquo_space; outer medulla&raquo_space; inner medulla

Question 20

What is the ratio of cortical nephrons to juxtamedullary nephrons

Answer 20

7 to 1

Question 21

What types of capillaries does the renal cortex contain?

Answer 21

glomerular and peritublar capillaries

Question 22

What types of capillaries does the renal medulla contain?

Answer 22

vasa recta capillaries only

Question 23

What is the sequence of vessels from the renal artery to the renal vein?

Answer 23

Renal Artery&raquo_space; Afferent Arterioles&raquo_space; Glomerular Capillaries&raquo_space; Efferent Arteriole&raquo_space; Peritubular Capillary&raquo_space; Intrarenal Vein&raquo_space; Renal Vein

Question 24

How does hydrostatic pressure change between the renal artery and vein?

Answer 24

It decreases with largest pressure decrease in afferent and efferent arterioles and smallest pressure decrease in the glomerular and peritubular capillaries

Question 25

Where does oncotic pressure increase?

Answer 25

glomerular Capillaries (concentration of plasma proteins during filtration)

Question 26

Where does oncotic pressure decrease?

Answer 26

Peritubular Capillaries (dilution of plasma proteins during reabsorption)

Question 27

Why do changes in the afferent arteriole and efferent arteriole affect Pgc and GFR?

Answer 27

Constriction of either causes an increase in resistance ->. decrease flow (RBF) Dilation of either increases flow (RBF) Afferent constriction means less of arterial pressure is transmitted to glomerulus -> dec Pgc -> dec GFR Efferent constriction elevates Pgc -> inc GFR Vice versa

Question 28

``` Do the following intrinsic factors vasoconstrict or vasodilate? endothelin nitric oxide adenosine prostaglandins dopamine ```

Answer 28

``` vasoconstrict vasodilate vasoconstrict vasodilate vasodilate ```

Question 29

What are the intrinsic autoregulation components

Answer 29

smooth muscle myogenic tubuloglomerular feedback intrinsic factors

Question 30

What is the autoregulatory range for arterial pressure and what happens to GFR?

Answer 30

100-180 mm Hg GFR and RBF increases at arterial pressure >180 mmHg GFR and RBF decreases at arterial pressure <100mmHg

Question 31

What happens with renal shutdown?

Answer 31

Occurs when arterial pressure <70 mm Hg | GFR = 0ml/min but kidney is still perfused, just no urine formed

Question 32

What happens with renal death?

Answer 32

Occurs when arterial pressure = 0 mm Hg | RBF =0ml/min; Kidney no longer perfused with blood

Question 33

Describe tubuloglomerular feedback

Answer 33

1. increased GFR 2. increased NaCl concentration in tubule fluid in Henle's loop 3. signal generated by macula densa of JGA 4. increased arterial resistance 5. GFR decreases

Question 34

How does a hemorrhage eventually lead to decreased renal excretion? List entire pathway.

Answer 34

hemorrhage -> dec arterial blood pressure -> inc renin secretion -> inc ANG II -> inc sodium and water reabsorption -> dec less renal excretion. ANG II also constricts renal arterioles -> dec RBF and GFR -> dec renal excretion dec arterial BP also inc sympathetic innervation to renal nerves -> inc renin secretion further and inc constriction of renal arteries

Question 35

How does severe hypoxia affect RBF and GFR

Answer 35

decreases RBF and GFR (seen with high altitudes)