054 Glomerular Filtration

Question 1

Which organ has the lowest arteriovenous O2 difference of any organs and why?

Answer 1

Kidney because they have high O2 uptake but blood flow is so high. The arteriovenous difference is 10%.

Question 2

What is the diameter of glomerulus?

Answer 2

200microns

Question 3

How many nephrons do we have in our kidneys?

Answer 3

2 millions

Question 4

What is nephrin?

Answer 4

Protein found in the diaphgram of the filtration slit

Question 5

What charge do the components of the filteration barrier carry?

Answer 5

-ve charge due to glycoproteins. This repels -ve charged solutes and attracts positively charged solutes. However for small solutes, the charge doesnt matter. Only plasma proteins (-ve) are repelled.

Question 6

What are the two factors of glomerular filtreation?

Answer 6

Electrical charge (+ve)
Molecular weight (smaller)

Question 7

Which can be filtrated more? Albumin or haemaglobin?

Answer 7

Haemaglobin because it is not as negatively charged.

Question 8

What occurs to renal blood flow and glomerular filtration rate during afferent arteriolar constriction?

Answer 8

Both renal blood flow and glomerular filtration rate decreases due to lower hydrostatic pressure

Question 9

What occurs to renal blood flow and glomerular filtration rate during efferent arteriolar constriction?

Answer 9

Increase in hydrostatic pressure causing glomerular filtration rate

Question 10

What is the effect of adenosine on arterioles in glomerulus?

Answer 10

Constricts the afferent arteriole, lowering filtration

Question 11

What is an example of a molecule that is able to constrict efferent arteriole constriction?

Answer 11

Angiotensin II

Question 12

What occurs when you block angiotensin II?

Answer 12

Efferent arteriolar dilation

Question 13

What occurs to renal blood flow and glomerular filtration rate during efferent arteriolar dilation?

Answer 13

High blood flow but low hydrostatic pressure, causing lower glomerular filtration.

Question 14

What occurs to renal blood flow and glomerular filtration rate during afferent arteriolar constriction?

Answer 14

High blood flow and higher hydrostatic pressure, causing higher glomerular filtration.

Question 15

How do prostaglandins and NO affect glomerular capillaries?

Answer 15

Dilate afferent arterioles

Question 16

What is the best way to test function of kidneys?

Answer 16

Total glomerular filtration rate. Using substance that can be 1. freely filtered, not reabsorbed and not secreted. One example is inulin, but we use creatinine clinically because there is no need for IV

Question 17

What is the typical value of renal blood flow?

Answer 17

1.2l/min

Question 18

What is the significance of autoregulatory change?

Answer 18

Keeping renal blood flow along with glomerular filtration constant despite changes in MAP

Question 19

Describe the myogenic mechanism of autoregulation?

Answer 19

Increase in blood pressure -> afferent arterial stretch -> non-specific cation channels open -> depolarization -> Ca2+ channels open -> afferent arteriole contracts

Question 20

What are two mechanisms of autoregulation of glomerular capillaries?

Answer 20

Myogenic mechanism

Tubuloglomerular feedback

Question 21

What is the MAP range of autoregulation?

Answer 21

90-180mmHg

Question 22

During haemorrhage, what occurs to the regulation of kidney vessels?

Answer 22

Reduced renal blood flow by sympathetic nerves. Circulating adrenaline acts similarly.

Question 23

What is tubuglomerular feedback?

Answer 23

A type of autoregulation mechanism. Macula densa cells sense changes in Na+ delivery and increased filtration associated with it. This stimulates release of adenosine, causing vasoconstriction of the afferent arteriole through paracrine mechanism.

Question 24

Why does tubuglomerular occur?

Answer 24

It is to protect against Na+ and fluid loss, resulting in a lower renal blood flow and so lower hydrostatic pressure.

Question 25

How much of total body weight do kidneys make up?

Answer 25

<0.05%

Question 26

What is the formula for net ultrafiltration pressure?

Answer 26

Net hydrostatic pressure - net oncotic pressure (oncotic pressure in bowman capsule 0)

Question 27

What is typical value for renal blood flow

Answer 27

1200mL/min

Question 28

What is the typical value for renal plasma flow

Answer 28

650mL/min

Question 29

What is typical GFR value?

Answer 29

120ml/min (20% filtration fraction)

Question 30

Describe the mechanism of tubuloglomerular feedback

Answer 30

Macula densa cells in the distal tube will detect changes in the Na+ absorbed, signalling hormones to constrict or dilate afferent arterioles e.g. adenosine to cause paracrine vasoconstriction.

Question 31

What are the renal consequences of an increased filtration rate?

Answer 31

Causes efferent blood to be more viscous. Decrease in circulating renin by both macula densa signals and also the viscous sluggish efferent blood flow.

Question 32

What are the consequences of GFR of an increased protein filtration?

Answer 32

Oncotic pressure of fluid in Bowmans capsule becomes significant, increasing fluid filtration.

Question 33

How much renal blood flow supplies the cortex?

Answer 33

More than 90%

Question 34

What substance can be used to measure renal plasma flow?

Answer 34

PAH

Question 35

How may the concept of renal clearance be used to estimate renal plasma flow?

Answer 35

At a low plasma PAH concentration, filtered level of PAH is low and PAH will be efficiently secreted into proximal tubule, thus PAH in renal vein will be 0. Hence renal plasma flow = clearance of PAH.