Organism level systems Study Guide

The body maintains a stable internal environment through a process called homeostasis. An important aspect of this is regulating blood glucose concentration. After a meal, carbohydrates are digested into glucose, which is absorbed into the bloodstream, leading to an increase in blood sugar levels. This rise is detected by the pancreas, an organ that contains specialised cells. In response, the pancreas releases a hormone called insulin directly into the blood.

Insulin travels through the bloodstream and acts on target cells, primarily in the liver and muscle tissues. It signals these cells to take up glucose from the blood. In the liver, insulin promotes the conversion of excess glucose into glycogen, a complex carbohydrate, for storage. Similarly, in muscle cells, glucose is taken up and used for immediate energy or converted into glycogen for storage. Insulin also encourages other body cells to take in glucose for cellular respiration.

As glucose is removed from the blood and stored, the blood glucose concentration decreases, returning to its normal, healthy range. This reduction in blood glucose then acts as a negative feedback signal to the pancreas, reducing the further release of insulin. This loop ensures that blood sugar levels do not drop too low. If blood glucose levels fall below the normal range, another hormone, glucagon (also produced by the pancreas), is released. Glucagon has the opposite effect of insulin; it signals the liver to convert stored glycogen back into glucose and release it into the blood, thus raising blood sugar levels. This intricate balance keeps the body's energy supply stable.