Modified Amino Acid Hormone:
Epinephrine

Explanation:
Epinephrine is a hormone that is produced and released by the adrenal glands, specifically the medulla. It is also known as adrenaline. Epinephrine is derived from the amino acid tyrosine, making it a modified amino acid hormone.

Structure and Function:
Epinephrine is a small molecule that belongs to the class of catecholamines. It consists of a catechol ring, which is derived from tyrosine, and an amine group. The amine group allows epinephrine to act as a neurotransmitter and hormone in the body.

Epinephrine plays a crucial role in the fight-or-flight response, which is the body's reaction to stress or danger. When the body perceives a threat, the adrenal glands release epinephrine into the bloodstream. This hormone then acts on various target tissues to prepare the body for action.

Functions of Epinephrine:
1. Increases heart rate and blood pressure: Epinephrine acts on the heart and blood vessels to increase heart rate and constrict blood vessels. This helps to deliver more oxygen and nutrients to the muscles and brain, preparing the body for physical exertion.

2. Dilates airways: Epinephrine relaxes the smooth muscles in the airways, allowing for increased airflow to the lungs. This helps to improve breathing during times of stress or exercise.

3. Mobilizes glucose: Epinephrine stimulates the breakdown of glycogen, a stored form of glucose, in the liver and muscles. This leads to an increase in blood glucose levels, providing a readily available source of energy for the body.

4. Enhances mental alertness: Epinephrine acts on the brain to increase alertness, focus, and attention. This helps to improve cognitive function during stressful situations.

Overall, epinephrine plays a vital role in the body's response to stress and helps to prepare the body for physical activity or emergency situations. Its structure, derived from the amino acid tyrosine, classifies it as a modified amino acid hormone.