Mechanical Digestion Research Paper

Mechanical digestion begins in the mouth, by chewing, using teeth. Incisors, cuspid, and bicuspids cut the foods into smaller pieces, and molars grind and crush food.

Then, saliva starts the chemical digestion, and causes complex carbohydrates to breakdown into smaller molecules. Amylase, an enzyme in saliva, breaks the chemical bonds in starches. Saliva contains lysozyme, which fights infection by digesting the cell walls of bacteria that enter into the mouth.

Chewed food, called bolus, is now pushed down through the throat. It enters the back of the throat called pharynx, instead to the lungs, because epiglottis closes the opening to the trachea.

Esophagus is a tube where the food can pass through. Inside, there is a muscle, called peristalsis, which helps the food to come down to stomach even without gravity. Cardiac sphincter, another muscle, closes the esophagus to prevent the contents in the stomach from flowing back.

It starts chemical digestion by releasing many substances from the stomach glands. In gastric gland hydrochloric acid is released. Another gland releases pepsin, which works well in acidic conditions, and breaks proteins into smaller polypeptide fragments. Mucus protects the stomach wall by lubricating, and if this layer fails, peptic ulcer may cause. Peptic ulcer is caused by the bacterium Helicobacter pylori, but it can be cured with antibiotics. Stomach does mechanical digestion by churning, which allows the chunks to breakdown further and enzymes to access better to the food. The mixture in the stomach is now called chyme. Then, pyloric valve, or pyloric sphincter, that connects stomach and small intestine, opens and allows chyme to move into the small