Alertness, pupillary dilation and piloerection are due to the effect of

Options

A. Melatonin
B. Corticoids
C. Catecholamines
D. Thyroxine

Answer

### Step-by-Step Solution

1. **Understanding the Question**: The question asks which hormone is responsible for alertness, pupillary dilation, and piloerection. These responses are typically associated with the body's reaction to stress or emergency situations.

2. **Identifying the Physiological Responses**:
- **Alertness**: This is a heightened state of awareness and readiness to respond to stimuli.
- **Pupillary Dilation**: This is the widening of the pupils, which allows more light to enter the eye, improving vision in low-light conditions.
- **Piloerection**: This is the contraction of the tiny muscles at the base of hair follicles, causing hairs to stand up, often referred to as "goosebumps." This can occur in response to cold or emotional states.

3. **Linking Responses to the Nervous System**: These physiological responses are primarily controlled by the sympathetic nervous system, which is activated during stressful or emergency situations.

4. **Hormonal Release**: When the sympathetic nervous system is activated, it stimulates the adrenal medulla to release certain hormones. The key hormones involved are:
- **Epinephrine (Adrenaline)**: Increases heart rate, dilates air passages, and is responsible for the 'fight or flight' response.
- **Norepinephrine (Noreadrenaline)**: Works alongside epinephrine to enhance alertness and prepare the body for action.

5. **Identifying the Correct Hormones**: The hormones released from the adrenal medulla during stress are collectively known as catecholamines. Therefore, the correct answer to the question is that alertness, pupillary dilation, and piloerection are due to the effects of catecholamines, specifically epinephrine and norepinephrine.

6. **Eliminating Incorrect Options**:
- **Melatonin**: Regulates sleep-wake cycles, not alertness.
- **Corticosteroids**: Primarily involved in metabolism and stress response but not directly linked to these specific responses.
- **Thyroxine**: Involved in regulating metabolic rate, not in acute stress responses.

### Final Answer
The correct answer is catecholamines (epinephrine and norepinephrine) released from the adrenal medulla.

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