Question

In the ascending limb of the loop of Henle, the maximum osmotic difference that can be created by the $N{a^ + }{K^ + }$ pump is approximately?
a. $\;100{\text{ mOsmol}{l^{ - 1}}}$
b. $\;200{\text{ mOsmol}{l^{ - 1}}}$
c. $\;300{\text{ mOsmol}{l^{ - 1}}}$
d. $\;400{\text{ mOsmol}{l^{ - 1}}}$

Answer 1

Blood in the body gets filtered by two reddish- brown bean shaped organs called kidneys. The structural and functional unit of kidneys are nephrons and it is equipped with such structures so as to facilitate the maintenance of water-electrolyte balance of the blood and remove the unwanted and toxic materials out.

Complete answer:
So, each kidney is divided majorly into two structures-
- The outer renal cortex and the inner renal medulla. Both the cortex and the medulla are spanned by urine-producing structural and functional units called nephrons.
- The initial filtration site is the renal corpuscle, located in the cortex to be followed by the renal tubules, passing from the cortex deep into the medullary pyramids.
- Medullary ray, which is a collection of renal tubules drain into a single collecting duct which descends down the renal pelvis to ultimately empty urine into ureter.

Renal tubules contain following parts:

Proximal convoluted tubules- involved with absorption and secretion in accordance with homeostasis.

Loop of Henle- hair-pin like structures in the medulla. It can further be divided into-
- Descending limb of loop of Henle- high permeability to water
- Ascending limb of loop of Henle- can further be studied in two parts, thin and thick ascending limb.
- Ascending limb of loop of Henle is impermeable to water but permeable to ions. Ions such as $N{a^ + }$, ${K^ + }$are actively reabsorbed with the help of $N{a^ + }{K^ + }$ pump located in the basolateral membrane, creating a concentration gradient by pumping out 3 ions of Na+ in exchange for $2$ ions of ${K^ + }$. Because the ascending limb is impermeable to water, the osmolarity of the interstitium increases resulting in an osmotic difference between the interstitium and fluid in the loop. It has been found that the maximum osmotic difference so obtained is $\;300{\text{ mOsmol}{l^{ - 1}}}$
Setting of a concentration gradient is the primary function of the loop of Henle.

Hence, the correct answer is option (C).

Note: There are mainly three steps for urine formation-

Filtration- blood entering the kidney gets filtered under high pressure and hence, called ultrafiltration.
Reabsorption- Required molecules, ions and solutes are reabsorbed into circulation, thus maintaining an optimum water- electrolyte balance in blood.
Secretion- some substances such as creatinine, hydrogen ions, and drugs are removed from blood. Osmolarity is the total number of solute particles present in one liter of solution, whereas Osmolality is the total number of solute particles in one kilogram of solvent.