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How Insulin Helps Cells Use Glucose
The key that unlocks the cell
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Insulin is a hormone that helps the body move glucose from the blood into cells, where it can be used for energy. After a meal, carbohydrates are broken down into glucose, causing blood glucose levels to rise. The pancreas senses this rise and releases insulin into the bloodstream. This matters because cells need glucose for fuel, but too much glucose left in the blood can damage organs over time.
Insulin works by binding to insulin receptors on the surface of many cells, especially muscle, fat, and liver cells. This binding acts like a signal that tells the cell to move glucose transporters to the cell membrane, allowing glucose to enter. In Type 1 diabetes, the body makes little or no insulin, so glucose has trouble entering cells. In Type 2 diabetes, cells become less responsive to insulin, so more insulin may be needed to move the same amount of glucose.
Key Facts
- Insulin is made by beta cells in the pancreas.
- Glucose is the main sugar used by cells for energy.
- Insulin + receptor binding sends a signal that helps glucose enter cells.
- Blood glucose rises after a meal and usually falls as insulin helps cells take up glucose.
- Normal fasting blood glucose is often about 70 to 99 mg/dL.
- Energy from glucose is released during cellular respiration: C6H12O6 + 6O2 = 6CO2 + 6H2O + energy.
Vocabulary
- Insulin
- Insulin is a hormone made by the pancreas that helps move glucose from the blood into body cells.
- Glucose
- Glucose is a simple sugar that cells use as an important source of energy.
- Insulin receptor
- An insulin receptor is a protein on a cell membrane that binds insulin and starts a signal inside the cell.
- Glucose transporter
- A glucose transporter is a membrane protein that allows glucose to pass into a cell.
- Diabetes
- Diabetes is a condition in which blood glucose stays too high because insulin is missing, not working well, or both.
Common Mistakes to Avoid
- Thinking insulin turns into glucose is wrong because insulin is a hormone signal, while glucose is a sugar fuel.
- Saying insulin directly pushes glucose through the membrane is wrong because insulin first binds to a receptor and triggers cell processes that allow transporters to help glucose enter.
- Confusing Type 1 and Type 2 diabetes is wrong because Type 1 usually involves little or no insulin production, while Type 2 usually involves insulin resistance.
- Assuming all cells need insulin to take in glucose is wrong because some cells, such as brain cells, can take up glucose without insulin-dependent transport.
Practice Questions
- 1 A student's blood glucose is 150 mg/dL after lunch and drops to 95 mg/dL after insulin helps cells absorb glucose. By how many mg/dL did the blood glucose decrease?
- 2 A pancreas releases 8 units of insulin after a meal. If Type 2 insulin resistance means the cells respond as if only 25% of that insulin is effective, how many effective units are the cells responding to?
- 3 Explain why a person with Type 1 diabetes may have high blood glucose even though their cells still need glucose for energy.