Blood brain barrier in adults have `"______"` junctions between cells

Options

A. tight
B. adhering
C. gap
D. none of these

Answer

To answer the question regarding the type of junctions present in the blood-brain barrier in adults, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Blood-Brain Barrier (BBB)**: The blood-brain barrier is a selective permeability barrier that separates the circulating blood from the brain and extracellular fluid in the central nervous system.

2. **Composition of the BBB**: The primary cells that make up the blood-brain barrier are endothelial cells, which line the blood vessels in the brain.

3. **Type of Junctions in Endothelial Cells**: In the blood-brain barrier, the endothelial cells are tightly packed together. This close packing is crucial for the barrier's function.

4. **Identifying the Junctions**: The junctions between these endothelial cells are known as "tight junctions." These tight junctions prevent the passage of most substances, thereby maintaining the integrity of the barrier.

5. **Function of Tight Junctions**: Tight junctions allow only small, lipid-soluble molecules and some gases to pass through freely while restricting larger and potentially harmful substances from entering the brain tissue.

6. **Conclusion**: Therefore, the correct answer to the question is that the blood-brain barrier in adults has "tight" junctions between cells.

### Final Answer:
Blood-brain barrier in adults have **"tight"** junctions between cells.

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