57. Regulating Blood Glucose

Blood glucose concentration refers to the amount of sugar in the bloodstream. It must be carefully balanced to ensure cells have enough fuel for respiration without damaging tissues.

1. High Blood Glucose and Insulin

When you eat carbohydrates, they are broken down into glucose and absorbed into the blood, causing a spike in glucose levels.

• Detection: The pancreas detects the rise in blood glucose.

• Hormone Released: The pancreas secretes insulin into the bloodstream.

• Mechanism: Insulin travels to cells (primarily liver and muscle cells) and triggers them to take in glucose from the blood.

• Storage: Inside these cells, glucose molecules are joined together to form glycogen, a large molecule used for long-term storage.

• Result: Blood glucose levels decrease back to the normal range.

2. Low Blood Glucose and Glucagon

If you haven't eaten for a while or have been exercising, your blood glucose levels may drop.

• Detection: The pancreas detects the low concentration of glucose.

• Hormone Released: The pancreas secretes glucagon.

• Mechanism: Glucagon travels to the liver.

• Conversion: It triggers the liver to break down the stored glycogen back into individual glucose molecules.

• Result: These glucose molecules are released into the blood, raising the concentration back to normal.

3. The Negative Feedback Loop

Insulin and glucagon work together in a cycle to maintain a stable internal environment (homeostasis).

• If glucose is too high: Insulin is released → Glucose is stored as glycogen → Blood glucose falls.

• If glucose is too low: Glucagon is released → Glycogen is converted to glucose → Blood glucose rises.

Because of this constant adjustment, blood glucose levels typically fluctuate slightly around an optimal level rather than staying perfectly flat.

Key Terms to Distinguish

• Glucose: The simple sugar used by cells for energy.

• Glycogen: The storage molecule made of many glucose units (found in liver/muscles).

• Glucagon: The hormone that triggers the breakdown of glycogen into glucose.

• Insulin: The hormone that triggers the storage of glucose as glycogen.

Summary Table: Blood Glucose Control