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Renal and Fluid-Electrolyte Physiology

Glomerular Filtration Rate Practice Questions

19 free Glomerular Filtration Rate practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 19 Medium

Which of the following describes the 'Filtration Fraction' and its typical normal value in a healthy adult?

  1. A The ratio of GFR to Renal Plasma Flow; approximately 20%
  2. B The ratio of Urine Flow to GFR; approximately 10%
  3. C The ratio of Renal Blood Flow to the GFR; approximately 50%
  4. D The ratio of GFR to Cardiac Output; approximately 5%

Correct answer: The ratio of GFR to Renal Plasma Flow; approximately 20%

The filtration fraction represents the proportion of the renal plasma flow that is actually filtered across the glomerular capillaries. In healthy kidneys, about 20% of the plasma entering the glomerulus enters the Bowman's space.

Question 2 of 19 Medium

What is the primary effect of Angiotensin II on the glomerular microcirculation at low to moderate concentrations?

  1. A Preferential dilation of the afferent arteriole
  2. B Preferential constriction of the efferent arteriole
  3. C Uniform dilation of both afferent and efferent arterioles
  4. D Direct inhibition of the podocyte filtration slits

Correct answer: Preferential constriction of the efferent arteriole

Angiotensin II preferentially constricts the efferent arteriole, which increases the glomerular capillary hydrostatic pressure. This mechanism helps maintain GFR even when renal perfusion pressure is low.

Question 3 of 19 Medium

If the hydrostatic pressure in Bowman's space increases due to a kidney stone obstructing the ureter, what is the most likely effect on GFR?

  1. A GFR will increase due to back-pressure
  2. B GFR will decrease because the net filtration pressure is reduced
  3. C GFR will remain constant due to autoregulation
  4. D GFR will increase substantially to flush out the ureteral obstruction

Correct answer: GFR will decrease because the net filtration pressure is reduced

Hydrostatic pressure in Bowman's space is an opposing force to filtration. An increase in this pressure, caused by downstream obstruction, reduces the net pressure gradient across the filtration barrier, thereby lowering GFR.

Question 4 of 19 Medium

The glomerular filtration barrier is highly selective based on which two physical properties of the molecule?

  1. A Color and density
  2. B Molecular solubility and temperature
  3. C Molecular size and electrical charge
  4. D Viscosity and pH

Correct answer: Molecular size and electrical charge

The basement membrane and podocyte slits restrict large molecules (size) and negatively charged molecules (charge). Since the basement membrane is lined with negatively charged glycoproteins, it repels other negative molecules like albumin.

Question 5 of 19 Medium

Tubuloglomerular feedback (TGF) involves a signal from the macula densa to the afferent arteriole. What is the specific trigger for this signal?

  1. A Increased delivery of NaCl to the distal tubule
  2. B Decreased blood pressure in the renal artery
  3. C Increased levels of circulating ADH
  4. D Decreased glucose levels in the proximal tubule

Correct answer: Increased delivery of NaCl to the distal tubule

When GFR increases, more NaCl reaches the macula densa cells in the thick ascending limb. These cells sense the increased salt and release paracrine factors like adenosine to constrict the afferent arteriole and normalize GFR.

Question 6 of 19 Medium

Which of the following Starling forces provides the primary drive for movement of fluid INTO the Bowman's space?

  1. A Glomerular capillary oncotic pressure
  2. B Bowman's space hydrostatic pressure
  3. C Glomerular capillary hydrostatic pressure
  4. D Plasma protein concentration in circulation

Correct answer: Glomerular capillary hydrostatic pressure

Glomerular capillary hydrostatic pressure is the pressure exerted by blood within the capillaries and is the only force that promotes filtration. All other forces, such as capillary oncotic pressure and capsular hydrostatic pressure, oppose it.

Question 7 of 19 Medium

Inulin is used to measure GFR because it meets which of the following criteria?

  1. A It is actively secreted by the proximal tubule
  2. B It is broken down and metabolized by the liver at a constant rate
  3. C It is freely filtered and neither reabsorbed nor secreted
  4. D It binds strongly to plasma albumin

Correct answer: It is freely filtered and neither reabsorbed nor secreted

Because inulin is handled by the kidney solely through filtration, the amount of inulin appearing in the urine per minute is exactly equal to the amount that was filtered. This makes the clearance of inulin an exact measure of GFR.

Question 8 of 19 Medium

Which change in the renal arterioles would result in the greatest possible increase in GFR?

  1. A Constriction of the afferent and dilation of the efferent arteriole
  2. B Dilation of the afferent and dilation of the efferent arteriole
  3. C Dilation of the afferent and constriction of the efferent arteriole
  4. D Constriction of the afferent and constriction of the efferent arteriole

Correct answer: Dilation of the afferent and constriction of the efferent arteriole

Dilating the afferent arteriole allows more blood into the glomerulus, while constricting the efferent arteriole prevents it from leaving easily. Both actions maximize the hydrostatic pressure within the glomerular capillaries, thus maximizing GFR.

Question 9 of 19 Medium

What is the typical GFR for a healthy, average-sized adult male?

  1. A 50 mL/min
  2. B 125 mL/min
  3. C 180 mL/min
  4. D 625 mL/min

Correct answer: 125 mL/min

A GFR of approximately 125 mL/min (or 180 L/day) is considered standard for a healthy male. This rate ensures that the entire plasma volume is filtered and processed by the kidneys multiple times per day.

Question 10 of 19 Medium

Which of the following substances would have the LOWEST renal clearance rate in a healthy individual?

  1. A Creatinine
  2. B Urea
  3. C Glucose
  4. D Sodium

Correct answer: Glucose

In a healthy person, glucose is freely filtered but then 100% reabsorbed in the proximal tubule, resulting in zero clearance. Creatinine and urea always have higher clearance rates because they are not fully reabsorbed (or are secreted).

Question 11 of 19 Medium

The myogenic mechanism of GFR autoregulation is a response to:

  1. A Chemical signals from the brain
  2. B Changes in the stretch of the afferent arteriole wall
  3. C Hormonal signals released by the adrenal cortex and medulla
  4. D The concentration of glucose in the blood

Correct answer: Changes in the stretch of the afferent arteriole wall

The myogenic mechanism is an intrinsic response of vascular smooth muscle; when increased blood pressure stretches the afferent arteriole, the muscle automatically constricts. This prevents high systemic pressure from being transmitted to the delicate glomerular capillaries.

Question 12 of 19 Medium

Which effect does sympathetic nervous system activation have on GFR during a 'fight or flight' response?

  1. A Increases GFR rapidly to help clear metabolic toxins from the blood
  2. B Increases GFR by dilating the renal artery
  3. C No significant effect, as renal blood flow remains constant
  4. D Decreases GFR via vasoconstriction of the afferent arterioles

Correct answer: Decreases GFR via vasoconstriction of the afferent arterioles

During high sympathetic stress, norepinephrine causes significant vasoconstriction of renal arterioles (primarily afferent). This shunts blood away from the kidneys toward vital organs like the heart and muscles, resulting in a decrease in GFR.

Question 13 of 19 Medium

Prostaglandins (PGE2 and PGI2) produced within the kidney primarily act to:

  1. A Constrict the afferent arteriole to lower GFR
  2. B Inhibit the release of Renin
  3. C Increase the permeability of the filtration slits
  4. D Dilate the afferent arteriole to protect GFR

Correct answer: Dilate the afferent arteriole to protect GFR

Prostaglandins act as vasodilators on the afferent arteriole. They are particularly important during states of low perfusion to oppose the vasoconstrictive effects of sympathetic nerves and Angiotensin II, thereby preventing renal ischemia.

Question 14 of 19 Medium

Which of the following would be expected to INCREASE the GFR?

  1. A A decrease in renal plasma flow
  2. B A decrease in the diameter of the afferent arteriole
  3. C An increase in the pressure within Bowman's capsule
  4. D A decrease in the concentration of plasma proteins

Correct answer: A decrease in the concentration of plasma proteins

Lower plasma protein levels result in lower colloid osmotic pressure. Since this pressure opposes filtration, reducing it allows more fluid to be filtered, effectively increasing GFR.

Question 15 of 19 Medium

In the calculation of GFR using clearance, what does the 'U' in the formula (U * V) / P represent?

  1. A Urea nitrogen concentration in the blood plasma
  2. B Urine flow rate in mL/min
  3. C Concentration of the substance in the urine
  4. D Uric acid clearance

Correct answer: Concentration of the substance in the urine

In the clearance formula, U is the concentration of the substance in the urine, V is the urine flow rate, and P is the concentration of the substance in the plasma. This formula determines the volume of plasma cleared of a substance per unit time.

Question 16 of 19 Medium

Why is creatinine clearance slightly higher than the actual GFR?

  1. A Creatinine is partially reabsorbed in the loop of Henle
  2. B Creatinine is synthesized by the bladder wall
  3. C Creatinine binds to glucose during transport
  4. D Creatinine is slightly secreted by the proximal tubules

Correct answer: Creatinine is slightly secreted by the proximal tubules

While creatinine is a good endogenous marker for GFR, about 10-20% of the creatinine in urine comes from secretion in the proximal tubule rather than just filtration. This leads to a slight overestimation of the GFR compared to the inulin standard.

Question 17 of 19 Medium

What happens to the filtration fraction if GFR remains constant but Renal Plasma Flow (RPF) increases?

  1. A Filtration fraction increases
  2. B Filtration fraction remains constant
  3. C Filtration fraction becomes zero
  4. D Filtration fraction decreases

Correct answer: Filtration fraction decreases

Since the filtration fraction is defined as GFR / RPF, increasing the denominator (RPF) while keeping the numerator (GFR) constant results in a smaller overall fraction or percentage.

Question 18 of 19 Medium

Which of the following is the most important factor in determining the 'coefficient of filtration' (Kf)?

  1. A The surface area and permeability of the glomerular capillaries
  2. B The length of the renal artery
  3. C The person's total body water volume
  4. D The concentration of sodium, potassium, and chloride in the diet

Correct answer: The surface area and permeability of the glomerular capillaries

Kf is a measure of the hydraulic conductivity and the total surface area available for filtration. Diseases that destroy glomeruli or thicken the basement membrane reduce Kf and consequently reduce GFR.

Question 19 of 19 Medium

Atrial Natriuretic Peptide (ANP) influences GFR by:

  1. A Dilating the afferent and constricting the efferent arteriole
  2. B Constricting both the afferent and efferent arterioles
  3. C Constricting the afferent and dilating the efferent arteriole
  4. D Inhibiting the heart's pumping force

Correct answer: Dilating the afferent and constricting the efferent arteriole

ANP increases GFR by simultaneously dilating the afferent arteriole and constricting the efferent arteriole. This dramatic increase in glomerular pressure promotes the excretion of sodium and water to reduce blood volume.

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