The first, fourth-fifth portion of the descending limb is lined by

Options

A. (a) Simple squamous epithelium
B. (b) Stratified squamous epithelium
C. (c) Cuboidal epithelium
D. (d) Columnar epithelium

Answer

To answer the question regarding the lining of the first, fourth, and fifth portions of the descending limb of the loop of Henle, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure**: The descending limb of the loop of Henle is part of the nephron, which is the functional unit of the kidney. It plays a crucial role in the reabsorption of water and the concentration of urine.

2. **Identify the Portions**: The question specifies the first, fourth, and fifth portions of the descending limb. It is important to note that the descending limb consists of both thick and thin segments.

3. **Recognize the Epithelium Types**:
- The first portion of the descending limb is lined with **cuboidal epithelium**.
- The second and third portions are lined with **simple squamous epithelium**.
- The fourth and fifth portions are also lined with **cuboidal epithelium**.

4. **Function of the Descending Limb**: The primary function of the descending limb is to reabsorb water. The thick segments (first, fourth, and fifth) are highly permeable to water, which aids in this process.

5. **Conclusion**: Based on the histological structure and the function of the descending limb, the first, fourth, and fifth portions are lined by **cuboidal epithelium**.

### Final Answer:
The first, fourth, and fifth portions of the descending limb are lined by **cuboidal epithelium**.

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