The Science of Nutrition

BIO 208

12/16/12

Written Assignment 2

1. Describe the body's mechanisms for controlling blood glucose levels under normal and stress conditions.

The blood glucose level is the amount of glucose (sugar) present in the blood of a human. Glucose is the primary source of energy for the body's cells and it is transported from the intestines or liver to body cells via the bloodstream, and is made available for cell absorption via the hormone insulin, produced by the body primarily in the pancreas. It is the fuel that provides energy to our body cell we get it from what we eat including proteins and carbohydrates and circulate through the bloodstream.

In the small intestine, glucose is absorbed into the blood and travels to the liver via the hepatic portal vein. The hepatocytes (liver cells) absorb much of the glucose and convert it into glycogen, an insoluble polymer of glucose. This is stored in the liver and can be reconverted into glucose when blood-glucose levels fall. As we eat, sleep, work, exercise, study and relax throughout the day, blood sugar levels fluctuate. Our bodies were designed to experience and take advantage of rising and falling blood sugar levels. After eating and digestion is complete and the absorption of nutrients decreases, the body is in a post-absorptive state and, as the body's cells use glucose to make energy, blood-glucose levels fall. In the absorptive state, an increase in blood glucose is detected by the beta cells of the pancreatic islets, causing them to increase the release of insulin into the blood. Several hours after eating a meal, when the body is in the post-absorptive state, insulin levels fall along with blood glucose and this result in the hormone glucagon being released by the alpha cells of the pancreas. However, stress floods the body with adrenaline and immediately makes large amounts of glucose available as part of the "fight-or-flight" mechanism. The stress response, are vital in emergencies, but through years of high-stress living, they become counter-productive and unhealthy. Regular exercise moderates blood sugar in two ways. As you exercise, your muscles use up glucose, immediately decreasing the sugar level in your blood.

The body mechanism has its own way of controlling blood glucose levels under normal and stress conditions.

2. Give several examples of soluble and insoluble dietary fibers. List food sources of these fibers. Contrast the physical characteristics and features of these two types of fiber and their effects on gastrointestinal tract function.

Dietary fibers are very good for the body and they are found naturally in the plants that we eat. They are parts of