Which of the following hormones is popularly known as the “emergency hormone” or “fight or flight hormone” because it is released rapidly in stressful or frightening situations?

Introduction / Context:
The human endocrine system secretes many hormones, each with specialised roles. Some hormones help us respond very quickly to sudden stress, danger or excitement. One such hormone prepares the body for immediate action by increasing heart rate, redirecting blood flow and mobilising energy sources. This hormone is often referred to as the emergency hormone or fight or flight hormone. The question asks you to identify which hormone has earned this nickname.

Given Data / Assumptions:

The hormone in question is released rapidly in emergency situations such as fear or stress. It prepares the body for fight or flight responses. Options include insulin, adrenaline, oestrogen, oxytocin and thyroxine. We assume standard human physiology definitions.

Concept / Approach:
Adrenaline (epinephrine) is secreted by the adrenal medulla in response to signals from the sympathetic nervous system during stress or danger. It increases heart rate, raises blood pressure, dilates airways, and stimulates the breakdown of glycogen to glucose, providing quick energy to muscles. Because it helps the body react instantly in emergencies, it is called the emergency hormone or fight or flight hormone. Insulin regulates blood glucose levels, oestrogen is a female sex hormone, oxytocin is involved in childbirth and bonding, and thyroxine regulates basal metabolism. None of these other hormones is primarily associated with sudden emergency responses.

Step-by-Step Solution:
Step 1: Link the phrase fight or flight to the sympathetic nervous system and adrenal medulla activity. Step 2: Recall that adrenaline is secreted in situations of fear, anger or stress, leading to rapid physiological changes. Step 3: Compare adrenaline with insulin, which reduces blood glucose, and thus does not fit the emergency response profile. Step 4: Note that oestrogen and oxytocin have major roles in reproduction and childbirth, not in emergency reactions. Step 5: Recognise that thyroxine regulates long term metabolic rate, rather than causing immediate fight or flight changes, so adrenaline is the only fitting choice.

Verification / Alternative check:
In textbooks, when the stress response is discussed, tables and diagrams clearly label adrenaline as the emergency hormone. They often list its effects: increased pulse, faster breathing, widened pupils and increased blood flow to muscles. Health education materials describing sudden fright or danger also refer to adrenaline rushes. You will not see similar descriptions tied to insulin, oestrogen, oxytocin or thyroxine. This clear association of adrenaline with rapid emergency responses confirms that it is the hormone the question is asking about.

Why Other Options Are Wrong:
Insulin lowers blood sugar after meals and acts relatively slowly compared with emergency responses; it is not released specifically in fight or flight situations. Oestrogen primarily regulates female secondary sexual characteristics and reproductive cycles. Oxytocin is important for uterine contractions during labour and for milk ejection during breastfeeding, and also plays a role in social bonding. Thyroxine affects basal metabolic rate and long term energy balance, not acute stress responses. Therefore, none of these can correctly be called the emergency hormone.

Common Pitfalls:
Some students may wrongly select thyroxine because they remember that thyroid hormones increase metabolism and energy, but this effect is gradual, not the immediate fight or flight response described in the question. Others may confuse adrenaline with noradrenaline or with general stress hormones like cortisol, but the famous nickname emergency hormone is most strongly attached to adrenaline. To avoid confusion, remember that adrenaline is secreted from the adrenal medulla during sudden stress, while cortisol comes from the adrenal cortex and works more slowly over longer periods.

Final Answer:
The hormone popularly known as the emergency or fight or flight hormone is adrenaline (epinephrine).