The chief role of insulin is to: a. stimulate cells to take up more glucose. b. stimulate the liver to break down stored glycogen into glucose. c. stimulate the pancreas to release glucagon into the blood. d. trigger the conversion of fatty acids and amino acids into glucose.
The correct answer and explanation is:
Correct Answer: a. stimulate cells to take up more glucose.
Insulin is a vital hormone produced by the beta cells of the pancreas in response to increased blood glucose levels, especially after eating. Its main function is to lower the concentration of glucose in the bloodstream. It does this primarily by stimulating cells throughout the body, especially in muscle, liver, and fat tissues, to take up glucose from the blood and use it for energy or store it for future use.
When blood glucose levels rise, insulin is secreted into the bloodstream. Once it reaches target cells, insulin binds to specific receptors on the cell surface. This activates a signal transduction pathway that causes glucose transport proteins (mainly GLUT4 in muscle and fat cells) to move to the cell membrane. These transporters allow glucose to enter the cell by facilitated diffusion. Once inside the cell, glucose can be used immediately for energy production or stored as glycogen in the liver and muscle.
This mechanism helps keep blood glucose levels within a narrow range, which is critical for maintaining homeostasis. Without insulin, or in conditions where insulin is not functioning properly, such as in diabetes mellitus, glucose remains in the bloodstream, leading to hyperglycemia. This can cause serious health complications over time, including damage to the eyes, kidneys, nerves, and cardiovascular system.
Other options listed are not correct because they reflect the actions of different hormones or processes. For example, glucagon, not insulin, stimulates the liver to break down glycogen into glucose during fasting. Insulin does not stimulate glucagon release; rather, it tends to suppress it. Additionally, insulin promotes the storage of nutrients, not their conversion into glucose through gluconeogenesis.
In summary, insulin’s primary role is to lower blood glucose by stimulating cells to absorb and utilize glucose, thus playing a crucial part in energy balance and metabolic control.