- The hormone that primarily acts to decrease plasma glucose concentration is Insulin.

- Insulin is secreted by the beta cells of the pancreatic islets in response to elevated blood glucose levels, such as after a meal.
- Its main function is to facilitate the uptake of glucose by cells, especially muscle and adipose tissue, thereby reducing the amount of glucose circulating in the blood.
- Insulin also promotes the storage of glucose as glycogen in the liver and inhibits the production of glucose by the liver (gluconeogenesis).

- In contrast, hormones like Glucagon, Cortisol, and Epinephrine work to increase plasma glucose concentration by stimulating glycogen breakdown, gluconeogenesis, and mobilization of energy stores to ensure adequate glucose availability during fasting, stress, or emergency situations.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th Edition, Chapter 79: Pancreatic Hormones and Diabetes Mellitus