Bicarbonate ions are relesed in exchange of chloride ions in lieum form

Options

A. Villi
B. Crypts of Lieberkuhn
C. Brush border cell
D. Valvulae conniventes/Plicae circulares

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks where bicarbonate ions are released in exchange for chloride ions in the ileum. The ileum is the final part of the small intestine.

2. **Identifying the Options**: The options provided are:
- Villi
- Crypts of Lieberkühn
- Brush border cells
- Valvuloconvulsions
- Plicae circulares

3. **Analyzing the Function of Each Option**:
- **Villi**: These are small, finger-like projections that increase the surface area for absorption but do not directly secrete bicarbonate ions.
- **Crypts of Lieberkühn**: These are glandular structures in the intestine that secrete intestinal juices but are not primarily responsible for bicarbonate secretion.
- **Brush Border Cells**: These are epithelial cells with microvilli on their surface, which are involved in the absorption of nutrients and can secrete bicarbonate ions.
- **Valvuloconvulsions**: These are folds in the intestine that help slow down the passage of food but do not have a role in bicarbonate secretion.
- **Plicae Circulares**: These are circular folds in the intestinal lining that increase surface area for absorption but do not secrete bicarbonate.

4. **Conclusion**: Based on the analysis, the brush border cells are responsible for the secretion of bicarbonate ions in exchange for chloride ions in the ileum.

5. **Final Answer**: The correct answer is **Brush Border Cells**.