Session 3 - Renal Blood Flow And GFR

Question 1

Name the blood vessels through which blood must pass to reach the glomerulus from the aorta.

Answer 1

Aorta —> Renal artery —> Segmental artery —> Interlobar artery —> Arcuate artery —> Interlobular artery —> Afferent arteriole —> Glomerular capillary

Question 2

What are the two types of nephron?

Answer 2

Cortical

Juxtamedullary

Question 3

Where in the kidney are cortical and juxtamedullary nephrons found?

Answer 3

Cortical nephron - outer part of cortex, extends just into the medulla
Juxtamedullary nephron - inner part of cortex next to medulla, extends deeper into the medulla

Question 4

Do cortical and juxtamedullary nephrons have large or small glomeruli?

Answer 4

Cortical nephron - small

Juxtamedullary nephron - large

Question 5

What are the differences between the loop of Henle of the cortical and juxtamedullary nephrons?

Answer 5

Cortical nephron - loop of Henle is shorter, mainly in cortex, just reaches into the medulla.

Juxtamedullary nephron - loop of Henle is longer, reaches into the inner part of the medulla.

Question 6

How do the diameters of the afferent and efferent arterioles differ in the cortical and juxtamedullary nephrons?

Answer 6

Cortical nephron: afferent arteriole > efferent arteriole

Juxtamedullary nephron: afferent arteriole = efferent arteriole

Question 7

How does the amount of sympathetic nerve innervation to cortical nephrons differ from juxtamedullary nephrons?

Answer 7

Cortical nephron - rich sympathetic nerve innervation

Juxtamedullary nephron - poor sympathetic nerve innervation

Question 8

How does the concentration of renin present differ between the cortical and juxtamedullary nephrons?

Answer 8

Cortical nephron - high concentration of renin

Juxtamedullary nephron - almost no renin

Question 9

What is the percentage of cortical and juxtamedullary nephrons present in the kidney?

Answer 9

Cortical nephron - 90%

Juxtamedullary nephron - 10%

Question 10

What is the average renal blood flow rate?

Answer 10

~ 1.1 L/min

Question 11

How do you calculate renal plasma flow?

Answer 11

Volume percentage of plasma in blood (1 - percentage volume of haematocrit) x renal blood flow

E.g. percentage plasma volume = 0.55
RBF = 1.1 l/min
0.55 x 1.1 l/min = 605 mL/min of plasma = renal plasma flow

Question 12

What percentage of blood passing through the glomerulus is actually filtered?

Answer 12

20% of blood from the renal artery is filtered at any one time. 80% of blood arriving exits unfiltered via the efferent arteriole.

Question 13

What makes up the renal corpuscle?

Answer 13

The glomerulus and Bowman’s capsule

Question 14

What is the function of the renal corpuscle?

Answer 14

To produce ultrafiltrate

Question 15

What sort of epithelium s the parietal layer of the Bowman’s capsule made of?

Answer 15

Simple squamous epithelium

Question 16

What cells make up the visceral layer of the Bowman’s capsule?

Answer 16

Podocytes

Question 17

What three layers make up the filtration barrier in a renal corpuscle?

Answer 17

Capillary endothelium
Basement membrane
Podocytes

Question 18

What molecules can be filtered from the glomerulus into the lumen of the Bowman’s capsule?

Answer 18

Water, salts and small molecules. Cells and large proteins can’t be filtered.

Question 19

How does the composition of ultrafiltrate produced in the renal corpuscle differ to the composition of blood?

Answer 19

Endometrium product of filtration is identical to plasma without the large proteins and cells.

Question 20

What is the basement membrane composed of?

Answer 20

It is an acellular gelatinous layer of collagen and glycoproteins.
Negative charge of glycoproteins helps to repel large proteins.

Question 21

What charge does the filtration barrier have and why?

Answer 21

Filtration barrier is negatively charged. Due to negative charge of glycoproteins in basement membrane.

Question 22

Why can cationic molecules pass through the filtration barrier more easily than anionic molecules?

Answer 22

Negative filtration barrier, attracts cation but repels anions.

Question 23

In many disease processes the negative charge on the filtration barrier is lost so that proteins are more readily filtered. What condition will this result in?

Answer 23

Proteinuria

Question 24

Which forces favour filtration and which forces oppose filtration?

Answer 24

Forces favouring filtration:
- hydrostatic pressure of plasma in glomerulus

Forces opposing filtration:

• hydrostatic pressure of ultrafiltrate in tubule
• oncotic pressure in glomerulus

Question 25

What is renal autoregulation?

Answer 25

Feedback mechanisms intrinsic to the kidney that keep renal blood flow (RBF) and glomerular filtration rate (GFR) constant.

Question 26

What mechanisms are involved in renal autoregulation?

Answer 26

Myogenic mechanisms

Tubuloglomerular feedback

Question 27

Why is autoregulation of GFR needed?

Answer 27

Without autoregulation a slight change in blood pressure would cause a significant change in glomerular filtration rate.

Question 28

Outline the myogenic response to an increase in renal blood pressure.

Answer 28

Increase in blood pressure —> afferent arteriole constricts —> GFR unchanged

Question 29

Outline the myogenic response to a decrease in blood pressure.

Answer 29

Decrease in blood pressure —> afferent arteriole dilates —> GFR remains unchanged

Question 30

Where are macula densa cells located?

Answer 30

Distal convoluted tubule, where the tubule comes into contact with the glomerulus.

Question 31

Describe what happens in tubular glomerular feedback.

Answer 31

1) A change in GFR causes a change in tubular flow rate and therefore changes the amount of NaCl that reaches the distal tubule.
2) Macula densa cells detect luminal [NaCl] in the distal convoluted tubule.
3) This stimulates the juxtaglomerular apparatus to release either adenosine (to reduce GFR) or prostaglandins (to increase GFR).

Question 32

How do macula densa cells monitor NaCl concentrations in the distal convoluted tubule?

Answer 32

Through concentration-dependent salt uptake via NaKCC co-transporters in the apical membrane of macula densa cells.

Question 33

What affect does adenosine have when released from the juxtaglomerular apparatus?

Answer 33

Acts on A1 receptors which cause constriction of afferent arteriole near the glomerulus, and A2 receptors which cause dilation of efferent arteriole.
Works to reduce glomerular filtration rate.

Question 34

What affect do prostaglandins have when released from the glomerulus?

Answer 34

Vasodilate the afferent arteriole.

Works to increase glomerular filtration rate.

Question 35

What is the role of glomerulotubular balance?

Answer 35

It reduces the amount of sodium excreted when GFR becomes to high despite the action of the myogenic response and tubular glomerular feedback. It does this by reabsorbing more of the filtered sodium.