Mark the second messenger in case of heart in response to parasympathetic nervous system.

Options

A. cAMP
B. cGMP
C. `IP_3`
D. `DG`

Answer

To determine the second messenger in the heart's response to the parasympathetic nervous system, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Role of the Parasympathetic Nervous System**:
- The parasympathetic nervous system is responsible for the "rest and digest" functions of the body. It helps to slow down the heart rate and promote relaxation.

2. **Identify the Second Messengers**:
- Second messengers are molecules that relay signals received at receptors on the cell surface to target molecules inside the cell. They play a crucial role in cellular signaling.

3. **Evaluate the Options**:
- **Option A: cAMP (Cyclic Adenosine Monophosphate)**: This is typically associated with the sympathetic nervous system and increases heart rate.
- **Option B: cGMP (Cyclic Guanosine Monophosphate)**: This is often involved in the signaling pathways of the parasympathetic nervous system.
- **Option C: IP3 (Inositol Triphosphate)**: This is involved in calcium mobilization but is not specifically linked to the heart's response to the parasympathetic system.
- **Option D: DG (2-Deoxyglucose)**: This is not a second messenger and is involved in glucose metabolism.

4. **Determine the Correct Answer**:
- Based on the evaluation, the second messenger that acts in the heart in response to the parasympathetic nervous system is **cGMP (Cyclic Guanosine Monophosphate)**.

### Final Answer:
The second messenger in the case of the heart in response to the parasympathetic nervous system is **cGMP**.

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