12. Glomerular filtration rate (GFR), extraction, clearance

Question 1

Glomerular filtration rate: what is it

Answer 1

GFR = The amount of filtrate produced per unit time by all of the nephrones of the two kidneys.

Question 2

Glomerular filtration rate: what do we need to choose to measure CFR

Answer 2

To measure the GFR we have to choose such a material, which is only filtered, it is neither secreted nor reabsorbed in the tubules.

Question 3

Glomerular filtration rate:Autoregulation of GFR:

Answer 3

It is constant even under wider periopheral arterial
midpressure changes. Beside the myogenic mechanism, the tubulo-glomerular feedback plays a role in this phenomenon.

Question 4

Glomerular filtration rate:Autoregulation of GFR: what is tubulo-glomerular feedback

Answer 4

Tubulo-glomerular feedback: The macula densa of the juxtaglomerular apparatus senses the volume
changes of the distal tubule and it probably secreted signals to adjust the GFR.

Question 5

Clearance: what is it

Answer 5

Is a measure of the volume of plasma completely freed of a given substance per unit time by the kidney
The ability of the kidney to remove a substance from the blood plasma and to forward it to the urine.

Question 6

Clearance: of PAH

Answer 6

The clearance of PAH is constant at low plasma
concentrations.

Question 7

Clearance: of PAH high conc

Answer 7

At higher concentrations the secretory capacity of
the tubules decreases, and the tubular cells become unable to secrete more PAH so therefore its clearance decreases.

Question 8

Clearance: of Insulin

Answer 8

Inulin is typically such a substance that is only filtered.Due to this, its concentration in the plasma does notinfluence its clearance even under extremely high values.

Question 9

Clearance: of urea simple

Answer 9

Therefore, clearance is smaller than that of inulin, but doesn’t depend on plasma concentration

Question 10

Clearance: of urea detail

Answer 10

Urea is freely filtered, and then passively moves among those parts of each tubule section, which are permeable for urea.
- A portion of the filtered amount of this substance always remains in the intersititum.

Question 11

Clearance: of glucose detail

Answer 11

Glucose is freely filtered, but under normal proximal tubular activity, glucose doesn’t get into the descending limb of Henle-loop. It is entirely reabsorbed in the proximal tubule.

Question 12

Clearance: of glucose simple

Answer 12

Therefore, under normal glucose plasma concentrations the clearance is 0.