First discovered hormone

Options

A. Thyroxine
B. Adrenaline
C. Secretin
D. Insulin

Answer

To determine the first discovered hormone from the given options (Thyroxine, Adrenaline, Secretin, and Insulin), we can follow these steps:

### Step 1: Understand the Hormones
- **Thyroxine (T4)**: This hormone is produced by the thyroid gland and is responsible for regulating the basal metabolic rate.
- **Adrenaline**: This hormone is secreted by the adrenal medulla and is known as an emergency hormone, often associated with the fight-or-flight response.
- **Secretin**: This hormone is released from the gastrointestinal tract (GIT) and stimulates the secretion of water and bicarbonate from the pancreas.
- **Insulin**: This hormone is produced by the pancreas and plays a crucial role in regulating blood glucose levels.

### Step 2: Identify the First Discovered Hormone
- Among these hormones, Secretin was the first hormone to be discovered. It was identified in the early 20th century (1902) by William Bayliss and Ernest Starling. They demonstrated that a substance secreted by the intestinal mucosa could stimulate the pancreas to secrete digestive juices.

### Step 3: Conclusion
- Therefore, the answer to the question "First discovered hormone" is **Secretin**.

### Final Answer:
The first discovered hormone is **Secretin**.

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