Question

If a substance has a transport maximum, Tm, for reabsorption, this means that

	a)    reabsorption is only passive
	b)    only a constant fraction of the substance will be reabsorbed
	c)    A and B
	d)    below a threshold level, all of the substance will be reabsorbed
	e)    none of the above

Measurements in a nephron reveal a glomerular hydraulic pressure of 69 mm Hg, and a fluid pressure in the Bowman's capsule of 15 mm Hg. Assuming that the plasma osmotic pressure is 30 mm Hg, and that essentially no plasma proteins are filtered by the glomerulus, what is the net glomerular filtration pressure in this case?

	a) -6 mm Hg
	b) 24 mm Hg
	d) 84 mm Hg
	e) 114 mm Hg
	c) 54 mm Hg

Answer 1

Ans1:- d)    below a threshold level, all of the substance will be reabsorbed.

transport maximum (tubular maximum) Tm , the highest rate in milligrams per minute at which the renal tubules can transfer a substance either from the tubular luminal fluid to the interstitial fluid or from the interstitial fluid to the tubular luminal fluid, beyond which it may be excreted in the urine.

Tubular absorption is a active process so option a) is wrong.

b) is wrong because a constant amount can be reabsorbed not constant fraction.

Ans 2:- 24 mmHg