What is the Difference Between Ascending and Descending Loop of Henle

The main difference between ascending and descending loop of Henle is that Ascending loop of Henle is permeable to ions, whereas descending loop of Henle is permeable to water.

Ascending and descending loops of Henle are the two parts of the thin part of the loop of Henle. It is lined by simple squamous epithelium.   

Key Areas Covered

1. What is Ascending Loop of Henle
– Definition, Features, Importance
2. What is Descending Loop of Henle
– Definition, Features, Importance
3. Similarities Between Ascending and Descending Loop of Henle
– Outline of Common Features
4. Difference Between Ascending and Descending Loop of Henle
– Comparison of Key Differences

Key Terms 

Ascending Loop of Henle, Descending Loop of Henle

What is Ascending Loop of Henle

Ascending loop of Henle is a part of the loop of Henle that occurs downstream to the descending limb. There are two parts of the ascending limb of the loop of Henle; the thin and thick ascending limb. The thick portion is the distal straight tubule, and the thin portion is the ascending loop of Henle. Also, the thick ascending limb occurs in the medulla of the kidney. Other parts of the ascending limb occur in the renal cortex. Significantly, the ascending limb of the loop of Henle is thicker than the descending limb.

Figure 1: Loop of Henle

Furthermore, the thin ascending limb is not permeable to water. However, it is permeable to ions and allows the reabsorption of sodium ions. The reabsorption occurs through passive diffusion. Na/K-ATPase is responsible for the reabsorption of ascending limb. In addition to that, the thick ascending limb that occurs in the medulla is impermeable to water. Sodium, potassium, and chloride ions reabsorption occurs through active transport. Active transport occurs through Na+/K+/Cl− co-transporter NKCC2 and the sodium/hydrogen exchanger NHE3. 

What is Descending Loop of Henle

Descending loop of Henle is the portion of the renal tubule that is the first portion of the loop of Henle. Significantly, it is impermeable to ions. Therefore, sodium or potassium ions do not pass through it. However, it is moderately permeable to urea and highly permeable to water. It readily absorbs water through osmosis. Also, it creates a strong osmotic gradient from descending limb to the ascending limb of the loop of Henle. Also, the concentration of urea increases dramatically in the descending limb.

Figure 2: Renal Tubule Function

Moreover, descending limb is thinner than the ascending limb of the nephron. 

Similarities Between Ascending and Descending Loop of Henle

• Ascending and descending loops of Henle are two parts of the thin part of the loop of Henle.
• It contains simple squamous epithelium.
• Their function is to absorb water and ions from the glomerular filtrate. 

Difference Between Ascending and Descending Loop of Henle

Definition

Ascending loop of Henle refers to a direct continuation from the descending limb of the loop of Henle while descending loop of Henle refers to the portion of the renal tubule that occurs in the first part of the loop of Henle.

Thickness

Ascending loop of Henle is thick, while descending loop of Henle is thin.

Function

Ascending loop of Henle is permeable to ions, while descending loop of Henle is permeable to water. 

Reabsorption of Ions

Ascending loop of Henle undergoes reabsorption of 25% potassium and a small amount of chloride ions, while descending loop of Henle undergoes no active reabsorption. 

Nephric Filtrate

Ascending loop of Henle makes the nephritic filtrate hypotonic, while descending loop of Henle makes the nephritic filtrate hypertonic. 

Conclusion

In brief, ascending and descending loops of Henle are two parts of the loop of Henle. Ascending loop of Henle is the direct continuation of the descending loop of Henle. It is thick. Also, it is permeable to ions. Additionally, it undergoes reabsorption of 25% potassium and a small amount of chloride ions. However, ascending loop of Henle makes the nephritic filtrate hypotonic. In comparison, descending loop of Henle is the continuation of the first part of the loop of Henle. It is thin. Further, it is permeable to water. But it does not undergo reabsorption of ions. It makes the nephritic filtrate hypertonic. Therefore, the main difference between ascending and descending loop of Henle is their permeability.

References:

1. Loop of henle. Loop of Henle – an overview | ScienceDirect Topics. (n.d.). 

Image Courtesy:

1. “Gray1128.” By Henry Vandyke Carter – Own work (Public Domain) via Commons Wikimedia
2. “Kidney nephron molar transport diagram” By Juvo415 – Own Work (CC-BY 3.0) via Commons Wikimedia