4/11: III - Glomerular Apparatus (JGA)

Question 1

What does the JGA mediate?

Answer 1

The TGF response

Question 2

What is the JGA composed of?

Answer 2

Juxtaglomerular cells
Macula densa cells in the wall of the TAL

Question 3

Describe JG cells

Answer 3

• Primarily in walls of afferent
  arterioles
• Secrete Renin

Question 4

Describe macula densa cells

Answer 4

• In close contact with JG cells
• Sense [Na+] and [Cl-] in filtrate

Question 5

What is the TGF response?

Answer 5

autoregulatory mechanism that is found in the kidney. Functions to keep GFR constant

Question 6

How can the TGF response be stimulated?

Answer 6

by decreased arterial pressure or by increased proximal NaCl reabsorption amount (high ECF amino acid or glucose content)

Question 7

What does a drop in GFR cause?

Answer 7

slower filtration rate through proximal tubule resulting in enhanced Na/Cl reabsorption (amount of NaCl that reaches macula densa is less than normal)

Question 8

What does the GRF increase result in?

Answer 8

reduced Na/Cl reabsorption and the proximal tubule increase Na/Cl delivery to the macula densa

Question 9

Describe the flow when there is low GFR

Answer 9

Question 10

What are stimuli for renin release?

Answer 10

• Drop in BP
• Drop in RBF
• Drop in NaCl delivery to Macula Densa (TGF response)

Question 11

What is the renin-angiotensin system?

Answer 11

Renin -> angiotensin I -> angiotensin II (converted via ACE)

Question 12

What is local control of RBF via?

Answer 12

Paracrines and autocrines

Question 13

What are vasoconstrictors?

Answer 13

Endothelin and dopamine

Question 14

What are vasodilators?

Answer 14

Prostaglandins, NO, bradykinin, dopamine

Question 15

What is systemic control via?

Answer 15

endocrine and nervous systems

Question 16

What does the SNS have a minor role in regulating?

Answer 16

RBF in normal state

Question 17

What does renal autoregulation smooth?

Answer 17

Normal SNS- induced changes in arterial pressure and cardiac output

Question 18

When is the SNS activated?

Answer 18

Stress (blood loss, cardiac events) can alter RBF

Question 19

What does SNS increase resistance of?

Answer 19

Both afferent and efferent arterioles

Question 20

What are factors that affect RBF and GFR?

Answer 20

Question 21

What are other factors that increase GFR and RBF?

Answer 21

1. High protein diet
2. High blood glucose levels

Question 22

What do these other factors lead to?

Answer 22

Pronounced increases in GFR

Question 23

What do increases in these other factors result in?

Answer 23

Reduced NaCl delivery to macula densa

Question 24

What does the TGF response function to do?

Answer 24

Keep NaCl delivery to macula densa constant

Question 25

How is filtered load calculated?

Answer 25

rate at which substances enter the nephron
o Units: amount/time
o Fx = (GFR)([X]plasma)

Question 26

How is excretion rate calculated?

Answer 26

rate at which substances are excreted
o Units: amount/time
o Ex = (Uv)([X]urine)
- Uv: urine flow rate

Question 27

How is clearance rate calculated?

Answer 27

determines the volume of blood cleared of a substance in a given amount of time
o Units: volume/time
o Clx = Ex / [X]plasma

Question 28

Describe the formula for substances that are filtered (and excreted) only

Answer 28

clearance rate can be used as an index for GFR

Question 29

Describe the formula for substances that are filtered and 100% secreted (and excreted)

Answer 29

clearance rate can be used as an index for RBF