Question

What for the ascending limb of Loop of Henle is permeable?
A. Glucose
B. Ammonia
C. Sodium-ion
D. Water

Answer 1

Hint: Henle's loop in the kidney is the section of a nephron that leads to the distal convoluted tubule from the proximal convoluted tubule.

Complete Answer:
The Henle loop generates a region of high urea concentration deep in the medulla, near the papillary duct in the collecting duct system, by means of a countercurrent multiplier system that uses electrolyte pumps. Water present in the filtrate flows out of the duct through
aquaporin channels in the papillary duct, passively flowing down its concentration gradient. This method reabsorbs water and produces urine for excretion that is concentrated.

Henle's loop can be split into four parts:
(I) Thin descending limb of Henle's loop: The thin descending limb, although being extremely permeable to water, has poor permeability to ions and urea. In the renal medulla, the loop has a sharp bend moving from descending to ascending thin arm.
(II) Thin ascending limb of Henle's loop: Water is impermeable to the thin ascending limb, but it is permeable to ions.
(III) Ascending limb of Henle's loop: By secondary active transport by a Na-K-Cl cotransporter (NKCC2), sodium ($Na^+$), potassium ($K^+$) and chloride ($Cl^−$) ions are reabsorbed from the urine. As well as other cations, such as magnesium ($Mg^{2 +}$) and calcium ($Ca^{2+}$), the electrical and concentration gradient drives further reabsorption of $Na^+$.
(IV) The thick ascending cortical limb: The thick ascending cortical limb drains urine into the convoluted distal tubule.

So the answer is “ Option C”.

Note: The loop type of tissue is a simple squamous epithelium. The terminology of "thick" and "thin" does not refer to the lumen scale, but to the scale of the epithelial cells. Often the loop is called the Nephron loop, too.