Question

If the GFR is 140 ml/min and the filtration fraction is 20%, then the renal plasma flow (RPF) is _______ ml/min.
A. 650
B. 700
C. 600
D. 2800

Answer 1

Hint:The amount of glomerular filtrate produced in all the nephrons of both the kidneys per minute is the glomerular filtration rate. It is around 125 mL/minute in a healthy person. A large amount of glucose, amino acids, sodium, potassium, urea, uric acid, ketone, and water are found in the glomerular filtrate.

Formula used: $$FF=GFR/RPF$$ where FF stands for filtration fraction, GFR stands for glomerular filtration rate and RPF stands for renal plasma flow .

Complete answer:
The glomerular filtration rate is called the rate at which kidneys filter blood. Blood pressure as it reaches the glomerulus is the main driving force for the filtering process or external pressure. Because of the hydrostatic pressure of the fluid inside the urinary space and the pressure produced by the proteins left in the capillaries, there appears to be a pullback of water into the circulatory system, this is counteracted to some degree by inward pressure (colloidal osmotic pressure).
Outward pressure minus inward pressure is the net filtration pressure, so Net Filtration= Outward pressure-inward pressure.
The juxtaglomerular apparatus in the kidneys carries out maintenance of the glomerular filtration volume. It is the region produced by the near-contact in a region between the distal convoluted tubule and the afferent arteriole.
When GFR falls, the release of renin activates JGA. Renin helps to return decreased GFR to normal.
The rate of GFR or Glomerular filtration is the amount of filtrate released per minute by the kidneys.
The volume of blood plasma that is distributed to the kidneys is called RPF or Renal plasma flow.
The ratio of GFR to RPF is filtration fraction or FF.
Hence, $$FF=GFR/RPF$$
 $$GFR=140ml/minandFF=20$$
By substituting the values,
$$0.20=140/RPF$$
$$RPF=140/0.20=700$$

Hence, the correct answer is option B-700.

Note: Dilation or constriction of the afferent arterioles may be adjusted by the kidney itself which counteracts changes in blood pressure. This intrinsic mechanism works over a wide blood pressure spectrum, but if you have kidney disease, it can fail.