The correct option is
B. Insulin.
Detailed Explanation:
- Understanding Blood Glucose Regulation:
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Blood glucose levels are crucial for maintaining energy homeostasis in the body. When we eat, carbohydrates are broken down into glucose, which enters the bloodstream. To prevent excessively high blood sugar levels, the body needs a mechanism to regulate this glucose.
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Role of Insulin:
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Insulin is a hormone produced by the beta cells of the pancreas. Its primary function is to lower blood glucose levels by facilitating the uptake of glucose into cells, particularly muscle and fat cells. When insulin is released into the bloodstream, it binds to insulin receptors on these cells, triggering a series of events that allow glucose to enter the cells through glucose transporters (GLUT).
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Mechanism of Action:
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Once insulin binds to its receptor, it activates a signaling pathway that promotes the translocation of GLUT4 (a type of glucose transporter) to the cell membrane. This process increases the number of glucose transporters available to transport glucose from the blood into the cells, effectively lowering blood glucose levels.
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Other Functions of Insulin:
- Besides promoting glucose uptake, insulin also plays a role in:
- Stimulating glycogenesis (the conversion of glucose to glycogen for storage in the liver and muscles).
- Inhibiting gluconeogenesis (the production of glucose from non-carbohydrate sources).
- Promoting lipogenesis (the conversion of excess glucose into fat).
Why the Other Options Are Incorrect:
- A. Glucagon:
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Glucagon is produced by the alpha cells of the pancreas and has the opposite effect of insulin. It raises blood glucose levels by promoting glycogenolysis (the breakdown of glycogen into glucose) and gluconeogenesis. Therefore, glucagon is not responsible for promoting glucose uptake into cells; rather, it works to increase blood glucose levels when they are low.
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C. Cortisol:
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Cortisol is a steroid hormone produced by the adrenal glands and is involved in the stress response. It increases blood glucose levels by promoting gluconeogenesis and inhibiting glucose uptake in non-essential tissues. While it plays a role in long-term glucose regulation, it does not primarily promote glucose uptake into cells.
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D. Adrenaline (Epinephrine):
- Adrenaline is also produced by the adrenal glands and is involved in the "fight or flight" response. It increases blood glucose levels by stimulating glycogenolysis and inhibiting insulin secretion. Like cortisol, it does not promote glucose uptake into cells; instead, it prepares the body for immediate energy needs by increasing available glucose.
Summary of Key Points:
- Insulin is the primary hormone responsible for lowering blood glucose levels by promoting glucose uptake into cells.
- It facilitates the translocation of glucose transporters to the cell membrane, allowing glucose to enter cells.
- Glucagon, cortisol, and adrenaline have opposing effects, primarily increasing blood glucose levels rather than promoting uptake.
- Understanding the roles of these hormones is crucial for grasping how the body maintains glucose homeostasis.