A chemical signal that has both endocrine and neural roles is

Options

A. calcitonin
B. epinephrine
C. cortisol
D. Melatonin

Answer

To answer the question "A chemical signal that has both endocrine and neural roles is:", we need to analyze the options provided and determine which chemical signal fits both categories.

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **Endocrine Role**: Refers to hormones that are secreted into the bloodstream and act on distant target organs.
- **Neural Role**: Refers to substances that act as neurotransmitters, transmitting signals between neurons.

2. **Evaluate the Options**:
- **Option 1: Calcitonin**:
- Secreted by the thyroid gland.
- Primarily involved in calcium metabolism.
- **Conclusion**: No neural role. (Not the answer)

- **Option 2: Epinephrine**:
- Secreted by the adrenal medulla.
- Known as the "emergency hormone" involved in the fight-or-flight response.
- Acts as a hormone in the bloodstream and is also released by adrenergic neurons as a neurotransmitter.
- **Conclusion**: Has both endocrine and neural roles. (This is a strong candidate)

- **Option 3: Cortisol**:
- Secreted by the adrenal cortex.
- Involved in carbohydrate metabolism and stress response.
- **Conclusion**: No neural role. (Not the answer)

- **Option 4: Melatonin**:
- Secreted by the pineal gland.
- Regulates sleep-wake cycles and other biological rhythms.
- **Conclusion**: No neural role. (Not the answer)

3. **Final Conclusion**:
- Based on the evaluations, **Epinephrine** is the only chemical signal that has both endocrine and neural roles. Therefore, the answer to the question is **Epinephrine**.