How the food changes consistency and form
Food first passes in the mouth where chewing or mastication is work done by the teeth, tongue, and saliva, which transforms the food into bolus – a soft, flexible, easily swallowed mass. After the bolus passes through the esophagus, it now enters the stomach where propulsion and retropulsion occurs. The continuous cycle of these movements results in the mixing of gastric contents with gastric juice, hence turning the bolus into a soupy liquid form called chyme. The small intestine now does most of the absorption process of nutrients. The large intestine turns chyme into a solid or semi-solid feces after it is stored for 3 to 10 hours. Materials in feces include bacteria, unabsorbed digested materials, and the left undigested parts of food that is removed out of the body through a process called defecation.
How the body was able to absorb the nutrients from the foods we eat.
Nutrient absorption is possible because of all parts of the digestive system that functions in mechanical and chemical digestion of the foods we eat. Since most of the carbohydrates we eat are starches, an enzyme called salivary amylase initiates the breakdown of starch into monosaccharides. Mucous cells in the stomach absorb some water, ions, and short-chain fatty acids. Small intestine is the site where most of the digestion and absorption of nutrients happens. The villi of mucosa increases the surface area of epithelium available for absorption and digestion. The villi and lacteals absorb fatty acids and fat-soluble vitamins, which are subsequently transported into the liver for storage and only released to cells when necessary.