You may be upset or tired or not feeling well. You're really not hungry, but you eat anyway. The food doesn't taste as good as usual, it's harder to swallow and you may notice a heavy feeling in your stomach. This can happen when the digestive system isn't ready with all the substances required. "The Language of Medicine" explains that the complex proteins, fats and carbohydrates we eat must all be broken down into simple forms to be absorbed by the body. This is the job of digestive juices, including enzymes.
The mouth.
Saliva is released by hunger signaled by the brain and added to by the sight and smell of food. Your mouth waters. The saliva aids the chewing of food by moistening it. Chewing moves the food around so it touches all parts of your tongue and reaches all the taste buds. The sense of smell also enhances the flavors. Saliva contains the first digestive enzyme, salivary amylase, that begins the breakdown of starch.
Esophagus
Hunger, chewing and swallowing stimulate the gastric secretions. The gastrointestinal system has its own nerve and hormone system to keep the digestive enzymes flowing as long as you're eating. When the food, now called a bolus, reaches the stomach, hormones begin to release enzymes and regulate the amount needed. There are also chemicals to signal that enough food has been consumed.
Stomach.
The acid in the stomach is a trigger for the release of a hormone and pepsinogen, the precursor to the enzyme pepsin that begins the breakdown of protein. The main function of the stomach itself is to break the food into small particles for digestion in the small intestine. The entire gastrointestinal tract is lined with mucus-producing cells to protect it from injury from food and from the strong stomach acid.
Small intestines
The small intestine secretes digestive enzymes. The pancreas and liver are considered accessory organs of digestion. Pancreatic amylase, lactase, lipase, maltase, nuclease, peptidase, sucrase and trypsin are all enzymes used in the digestive process. Most of these are used in the duodenum, the first section of the small intestine. If your body does not produce a particular enzyme or not enough of it, you will have difficulty digesting that food. Deficiency of the enzyme lactase is common in adults and makes the milk sugar lactose hard to digest.
Large Intestine
By the time the food has passed through the small intestine, the majority of it has been broken down into simple forms and has passed into the bloodstream for distribution first to the liver for further processing and then to the cells. The primary function of the large intestine itself is to remove excess water from the digested food and store it for excretion. The large intestine does not secrete enzymes but does contain many helpful bacteria that use their own enzymes to digest what they can of our leftovers and secrete vitamin K as well as some B vitamins and amino acids.
References
- "The Language of Medicine (6th Edition)"; Davi-Ellen Chabner, B.A.,M.A.T.;2001
- "Handbook of Pathophysiology (3rd Edition) "; Corwin, Elizabeth J., MSN, PhD, FNP; 2008
- Gastroenterology Nursing Issue: Volume 23(4), July/August 2000 pp.194-195
- CliffsNotes.com. Digestive Enzymes. 20 Aug 2010
