How digestion works problems issues



The purpose of digestion is to free nutrients by breaking down the large molecules in which most are found into simpler forms small enough (and soluble enough) to pass from the digestive system into the cells where they are needed. However, these nutrients are worthless if digestion is impaired.

Digestion incorporates a wide variety of mechanical and chemical steps that are suited to breaking down particular types of nutrients. Hormonal processes come into play before, during, and after digestion since the secretions and muscular movements of the digestive tract can be triggered by hormonal secretions or inhibited in part by psychological factors outside the body. The mechanical processes take place throughout the entire cycle of digestion. The chemical processes act, by means of acids, enzymes, and alkalis, primarily on proteins, fats, and carbohydrates, since vitamins and minerals are able to be absorbed for the most part by the body in their original form, once they are split off from the foods that bind them.

Water is a vital medium in the entire digestive process, aiding secretions in softening, diluting, and dissolving nutrients and in transporting them to the cells. In the mouth, food begins to be broken down both mechanically and chemically. It is masticated; or chewed, and reduced to small particles that are more accessible to digestive chemicals. The chewed food mixes with saliva and becomes softer and easier to swallow, while ptyalin, an enzyme in the saliva, begins to chop up starches in the food into their constituent molecules of simpler sugars.

While the food remains in the mouth, its pleasant taste creates a stimulus for continued eating and for secretion of more saliva. The food is then pushed farther into the digestive system by swallowing, a reflex contraction caused by the presence of food on the back of the tongue. Wavelike muscular motions (called peristalsis) propel the food through the esophagus (in about five seconds) then through the cardiac sphincter, a circular band of muscle that guards the entrance to the stomach and prevents food from returning to the esophagus.