Describe adrenaline as the hormone secreted in ‘fight or flight’ situations and its effects, limited to: (a) increased breathing rate (b) increased heart rate (c) increased pupil diameter

Adrenaline, also known as epinephrine, is a hormone secreted by the adrenal glands during fight or flight situations. This hormone plays a crucial role in preparing the body to respond to perceived threats by triggering various physiological changes. Here’s a detailed description of its effects, specifically focusing on increased breathing rate, increased heart rate, and increased pupil diameter.

(a) Increased Breathing Rate

• Mechanism: Adrenaline stimulates the dilation of the airways (bronchodilation) in the lungs, facilitating increased airflow. This response is mediated by the relaxation of smooth muscles in the bronchial passages.
• Effect: As a result, the breathing rate increases, allowing for greater oxygen intake. This is essential during stressful situations when the body requires more oxygen to fuel muscles and maintain energy levels for rapid action.

(b) Increased Heart Rate

• Mechanism: Adrenaline acts on the heart by binding to beta-adrenergic receptors, which leads to an increase in heart rate (tachycardia). It enhances the speed and force of cardiac contractions.
• Effect: The increased heart rate ensures that more blood is pumped throughout the body, delivering oxygen and nutrients to vital organs and muscles. This heightened circulatory response prepares the body for immediate physical activity, whether it be fighting or fleeing from danger.

(c) Increased Pupil Diameter

• Mechanism: Adrenaline causes the dilation of the pupils (mydriasis) by stimulating the radial muscles of the iris. This allows more light to enter the eye.
• Effect: The enlargement of pupil diameter improves vision by enhancing visual acuity and peripheral awareness, enabling individuals to better assess their environment during stressful situations.

Summary of Effects of Adrenaline