141 - 2 - Kidney Function I

Question 1

What does kidney autoregulation do?

Answer 1

Alters resistance of the afferent arteriole to maintain GFR.

Question 2

Implication of a resistance vessel

Answer 2

Pressure will drop across the length of vessel

Question 3

Role of the afferent arteriole

Answer 3

Maintains pressure gradient of glomerular capillary at 50mmHg

Question 4

Pressure drop between afferent and efferent arteriole

Answer 4

From 100mmHg to 10mmHg

Question 5

Pressure in peritubular capillaries

Answer 5

~5-10mmHg

Question 6

Effect on GFR of constricting afferent arteriole

Answer 6

Decrease GFR (decreased hydrostatic pressure)

Question 7

Effect on GFR of constricting efferent arteriole

Answer 7

Increase GFR (increased hydrostatic pressure)

Question 8

Blood pressures between which autoregulation can maintain a constant GFR

Answer 8

Mean arterial blood pressure between 80 and 180mmHg

Question 9

Average GFR

Answer 9

180L/day

Question 10

Mechanisms leading to autoregulation
1
2

Answer 10

1) Myogenic response (contraction to resist distension)

2) Tubuloglomerular feedback (TGF)

Question 11

Part of Bowman’s capsule that is responsible for myogenic response

Answer 11

Afferent arteriole

Question 12

Part of nephron responsible for tubuloglomerular response

Answer 12

Macula densa (where junction between ascending limb and distal tubule are in contact with afferent and efferent arterioles of the same nephron)

Question 13

*Location of juxtaglomerular apparatus

Answer 13

JUXTAGLOMERULAR

Question 14

Unusual cell type in afferent arteriole

Answer 14

Layer of granular cells

Question 15

Role of juxtaglomerular apparatus

Answer 15

Monitors amount of glomerular flow (by measuring chloride concentration).
If there is too much, makes glomerulus filter less

Question 16

Role of macula densa cells in GFR regulation
1
2
3

Answer 16

1) If there is a greater flow rate from increased GFR, there will be more Cl- detected by macula densa cells
2) Ca2+ channels will open on macula densa cells, triggering a paracrine signal which stimulates paracrine factor release (most importantly adenosine).
3) Adenosine acts on granular cells (which have adenosine type 1 receptors), which makes them vasoconstrict. This reduces GFR.

Question 17

Part of kidneys from which renin is released

Answer 17

Granular cells of the afferent arteriole

Question 18

Amount of filtered water that is excreted

Answer 18

1%

Question 19

Amount of filtered creatinine that is excreted?

Answer 19

100%

Question 20

Why is GFR high, if most of what is filtered is reabsorbed?

Answer 20

To filter toxic substances that are present in small amounts (EG: bilirubin, creatinine)

Question 21

Renal clearance

Answer 21

Excretion rate of a substance relative to plasma concentration.
Excretion/plasma concentration of substance

Question 22

What does renal clearance tell you?

Answer 22

The volume of plasma cleared of particular substance per time

Question 23

How is GFR estimated?
1
2
3

Answer 23

1) Use inulin (a substance that is freely filtered, not reabsorbed or secreted).
2) Establish stable plasma concentration of inulin
3) Amount of inulin is measured, which is directly proportional to GFR, as inulin isn’t reabsorbed or secreted.

Question 24

Good approximation of GFR 
1
2
3
4

Answer 24

1) Measure creatinine clearance per unit time.
2) Measure creatinine concentration in urine
3) Creatinine is at a constant level in blood normally.
4) Creatinine is filtered, not reabsorbed. Secreted at a low rate (so not a perfect measure).

Question 25

What might it mean if there is glucose in urine?

Answer 25

Too much glucose in blood being filtered, and is overloading the kidney’s ability to reabsorb glucose.

Question 26

Amount of filtered glucose that is reabsorbed

Answer 26

100%

Question 27

Rate of penicillin clearance

Answer 27

150mL minute

Question 28

What is strange about rate of penicillin clearance?

Answer 28

It is greater than GFR

Question 29

How is the rate of penicillin clearance greater than GFR?

Answer 29

100% of filtered penicillin is excreted.

Some additional penicillin is secreted into the proximal/distal tubule from the interstitial fluid.

Question 30

How can penicillin have an active transporter into the proximal and distal tubules?

Answer 30

Transporter is not specific to penicillin.

Transports toxic acidic molecules (EG: probenecid)

Question 31

Why could it be beneficial to co-prescribe penicillin and probenecid?

Answer 31

Both compete for binding to active transporter that secretes these substances into the proximal/distal tubules.
Slows clearance of penicillin.