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This MCQ tests your knowledge of the physiological and pathophysiological principles behind the GFR.

Reviewed by Jonathan Loomes-Vrdoljak

Glomerular filtration and assessment of renal function

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Question 1

What is glomerular filtration rate (GFR)?

A
The concentration of metabolites that are filtered by one kidney / unit time
B
The volume of water reabsorbed by the kidneys/ unit time
C
The total volume of filtrate formed by all nephrons in both kidneys/ unit time
D
The volume of filtrate that is reabsorbed by the kidneys/ unit time
Question 2

How is glomerular filtration rate (GFR) altered by acute kidney injury?

A
Increased
B
Decreased
C
Remains unchanged
D
Only reabsorption is altered
Question 3

How is GFR calculated?

A
GFR = ClX = (UX)
B
GFR = Kf x NFP
C
GFR = PG – PB – πG + πB
D
GFR = Urinary excretion rate = Filtration rate + Secretion rate – Reabsorption rate
Question 3 Explanation: 
Kf is the filtration constant/coefficient (that is a factor of membrane permeability and surface area) and NFP is the net filtration pressure.
Question 4

Which parameter of the GFR equation does diabetic nephropathy most likely alter?

A
Kf, as the surface area available for filtration is reduced
B
Kf, as membrane permeability is increased
C
NFP as the oncotic pressure if the blood is increased
D
NFP as the oncotic pressure if the filtrate is increased
Question 4 Explanation: 
The first detectable change in the kidneys is a thickening of the basement membrane (see https://unckidneycenter.org/kidneyhealthlibrary/glomerular-disease/diabetes/ for a good picture) and over time the damage leads to them being unable to filter the blood any further, so you get a reduced surface area and a reduced GFR. Confusingly, despite damage to and thickening of the filtration membrane, there is often an increase in protein in the filtrate; however, as we see a reduction in GFR we can assume that the effect of surface area plays a bigger role that oncotic pressures and therefore A is the correct answer.
Question 5

What is Net Filtration Pressure (NFP)?

A
NFP = PG + PB – πG + πB
B
NFP = PG – PB + πG + πB
C
NFP = PG – PB – πG - πB
D
NFP = PG – PB – πG + πB
Question 6

Your patient has liver failure and is unable to produce albumin. How does this affect the net filtration pressure (NFP)?

A
The Bowman’s capsule colloid pressure increases, reducing NFP
B
Blood plasma oncotic pressure decreases, increasing NFP
C
Blood plasma oncotic pressure increases, increasing NFP
D
Blood plasma hydrostatic pressure increases, increasing NFP
Question 6 Explanation: 
Albumin plays a major role in providing oncotic pressure in the blood so a reduction would mean that NFP would increase because there was less protein holding water back from entering the filtrate. In truth, the situation is a lot more complicated then that as the reduced protein would also lead to reduced blood pressure.

For a more comprehensive discussion of the relationship between liver disease and GFR see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4552961/.

Question 7

What is the main way the body regulates GFR with reference to the equation GFR = Kf x NFP?

A
By altering net filtration pressure, specifically by altering PG
B
By altering net filtration pressure, specifically by altering PB
C
By altering blood plasma oncotic pressure, πG
D
By altering filtrate oncotic pressure, πB
Question 7 Explanation: 
PG is the hydrostatic pressure in the glomerulus.
Question 8

Which of the following is false?

A
Dilation of the afferent arteriole or constriction of the efferent arteriole increases GFR
B
Angiotensin 2 constricts the efferent arteriole, increasing GFR
C
Prostoglandins and atrial natriuretic peptide dilate the afferent arteriole, increasing GFR
D
Noradrenaline, adenosine and endothelin dilate the afferent arteriole increasing GFR
Question 8 Explanation: 
Noradrenaline, adenosine and endothelin are vasoconstrictors and decrease AA diameter, reducing GFR
Question 9

A patient takes NSAIDs for their backache. What effect can we expect this drug to have on that patient’s GFR?

A
Increase
B
Decrease
C
Partially increase
D
No change
Question 9 Explanation: 
Prostaglandins dilate the afferent arteriole of the kidney. NSAIDs block the synthesis of prostaglandins, thus reducing their dilation capability on the afferent arteriole, reducing GFR.
Question 10

The kidney maintains a constant renal blood flow rate between 80 and 180 mmHg. The kidney can partly autoregulate this pressure by responding to changes detected by stretch receptors. What name is the given to this mechanism?

A
Myogenic response
B
Myotonic response
C
Myotactic response
D
Myoglomerular response
Question 10 Explanation: 
Myogenic response - where the increase in blood flow stretches smooth muscle in blood vessels, causing calcium to be released and constriction of the blood vessel to occur, reducing blood flow to the distal blood vessels of the nephron.
Question 11

If sodium and chloride transport in the early DCT was blocked, how would this impact the kidneys' ability to maintain a constant renal flow rate?

A
The myogenic response is impaired as depolarisation and subsequent muscle contraction is started by sodium influx into the cell
B
The tubuloglomerular response would not be activated by the macula densa cells
C
The juxtaglomerular cells are unable to release renin
D
There would be no impact on the renal flow rate as these transporters are present in the late DCT
Question 11 Explanation: 
If all sodium and chloride transport was blocked in the early DCT there would be no tubuloglomerular feedback. The macula densa cells are found in the early distal tubule and sense the concentration of sodium and chloride in the filtrate. If there is too much sodium chloride, the macula densa triggers a cascade of reactions that release adenosine to constrict the afferent arterioles; if there is too little sodium chloride the macula densa triggers the release of renin, which ultimately causes angiotensin II to constrict the efferent arterioles. Therefore, no sodium and chloride entry into the macula densa would lead to constriction of the efferent arterioles.
Question 12

Describe the cascade of events that result from the detection of low blood pressure by the kidney

A
Renin is released by juxtaglomerular cells —> Renin converts angiotensinogen to angiotensin I —> angiotensin I is converted to angiotensin II by angiotensin converting enzyme
B
ADH is released by juxtaglomerular cells —> ADH converts angiotensinogen to angiotensin I —> angiotensin I is converted to angiotensin II by angiotensin converting enzyme
C
Renin is released by juxtaglomerular cells —> dilates the afferent arteriole
D
Renin is released by juxtaglomerular cells —> constricts the efferent arteriole
Question 13

Why is ramipril prescribed for patients with hypertension?

A
Pharmaceutical companies are peddling a useless drug
B
It blocks the conversion of angiotensin I to angiotensin II reducing blood pressure
C
It blocks the conversion of angiotensinogen to angiotensin I reducing blood pressure
D
It catalyses the conversion of angiotensinogen to angiotensin I reducing blood pressure
Question 13 Explanation: 
It blocks the conversion of angiotensin I to angiotensin II. Angiotensin II causes vasoconstriction of blood vessels and an increase in blood pressure.
Question 14

Which investigations are not helpful in identifying kidney abnormalities?

A
Urine sample
B
Blood sample
C
Kidney biopsy
D
Peak flow rate
Question 14 Explanation: 
Urine samples help to detect whether there any substances that are not normally supposed to be present in the urine such as blood, protein, leukocytes, glucose Blood samples help to detect whether the substances that are failing to be excreted by the kidneys are building up in the blood. ex. Urea and creatinine Kidney biopsies are helpful in detecting whether structural abnormalities are present in the kidney Peak flow rate is a lung function test
Question 15

What is the best overall indicator of kidney function?

A
GFR
B
Blood urea
C
Glycosuria
D
Proteinuria
Question 16

Your patient has a urine production rate of 2 ml/min, excretes your metabolite of interest at 2 mg/ml, and is present in their blood plasma at 4 mg/ml.  Calculate the patient’s renal clearance.

A
4ml/min
B
3ml/min
C
2ml/min
D
1ml/min
Question 16 Explanation: 
Renal clearance = (rate of urine production x substance concentration in urine) / substance concentration in blood.
Question 17

What is the relationship between the renal clearance of creatinine and GFR?

A
Creatinine is not filtered or secreted
B
Creatinine is filtered and secreted and thus overestimates GFR
C
Creatinine is filtered and reabsorbed, so it underestimates GFR
D
Creatinine is completely reabsorbed, and thus is of no value as a marker for GFR
Question 18

One of your patients is a body builder. You take a urine sample and find that their urine creatinine is equal to the GFR of someone fitting their demographic, how do you interpret this result?

A
This is a normal result. Their GFR is better than that of the normal population because they are fit.
B
This is an abnormal result. Their GFR is reduced as creatinine normally overestimates GFR and they are a body builder.
C
This is a normal result. Creatinine is involved in the production of muscle so you would expect that body builders would excrete less.
D
This is a normal result. Serum creatinine underestimates GFR.
Question 19

What is a limitation of estimating GFR using serum creatinine?

A
You can lose 50% of your kidney function and still have normal creatinine levels
B
The sample is expensive to process
C
The sample is difficult to obtain
D
There are no limitations
Question 20

Which variable does not alter serum creatinine concentrations?

A
Age
B
Sex
C
Malnutrition
D
Sexual orientation
Question 21

What parameters are used to create an eGFR calculation?

A
Serum creatine, age, sex, ethnicity, muscle mass
B
Serum creatine, age, sex
C
Serum creatine, age, sex, ethnicity
D
Serum creatine, age, muscle mass
Question 21 Explanation: 
One limitation of the eGFR calculation is that it does not take muscle mass into consideration.
Question 22

A patient with an amputation presents to clinic. How do you expect their actual GFR to be related to the eGFR that you have calculated?

A
The patient’s eGFR will underestimate the patient's true GFR
B
They will both be the same
C
The patient’s eGFR will overestimate the patient's true GFR
D
The amputation has nothing to do with their GFR
Question 22 Explanation: 
As the patient has lost a limb they will have less circulating creatinine (as they have less muscle mass). As the eGFR calculation does not take account of the patient's muscle mass it assumes the reduced creatinine concentration in the blood is due to increased filtration of creatinine by the kidneys and therefore give a higher eGFR.
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