Name the tissues where the following structures occur :
Single-unit smooth muscles

Explanation

**Step-by-Step Solution:**

1. **Understanding Single-Unit Smooth Muscles**:
- Single-unit smooth muscles are a type of smooth muscle tissue that function as a single unit. They are characterized by their ability to contract in a coordinated and synchronous manner.

2. **Identifying Locations**:
- These muscles are primarily found in the walls of certain vital organs. Vital organs refer to those that are essential for survival and are located internally in the body.

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