What do mast cells secrete ?

Explanation

### Step-by-Step Solution:

1. **Identify the Type of Cells**: Mast cells are a type of connective tissue cell found in various parts of the body, particularly in the mucosa and skin.

2. **Understand the Role of Mast Cells**: They play a crucial role in the immune response, acting as a first line of defense against foreign antigens that enter the body.

3. **Granules in Mast Cells**: Mast cells contain granules that are rich in specific substances, primarily histamines and heparin.

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