What are two chemical substances released into the blood by the mast cells? Specify the effect of each

Explanation

### Step-by-Step Solution:

1. **Introduction to Mast Cells**:
- Mast cells are a type of immune cell that play a crucial role in the body’s defense against foreign particles and pathogens. They are primarily located in tissues such as the skin and mucosa.

2. **Chemical Substances Released**:
- Mast cells release several chemical substances into the blood, but two key substances are **heparin** and **histamine**.

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