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How does the food change in consistency and form?
The digestion process begins in the mouth where there is a physical breakdown of the food. Using our teeth, we break down the large pieces of food into small pieces by chewing. The chemical breakdown of food happens when the saliva secreted by the salivary glands breaks down the starch into maltose using salivary amylase. The food is now a rounded mass called bolus. After swallowing, the bolus passes down the esophagus through the process of peristalsis, and then reaches the stomach. The stomach muscles then churns and mixes the bolus with gastric juices that contain enzymes which break down the food into even smaller pieces. The food is now a thick semi-fluid called chyme. After the absorption of nutrients and water in the small and large intestine, defecation is bound to happen in order to eliminate the remaining indigestible residues called feces.
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How could the body absorb the nutrients from the foods we eat?
When chyme is transported into the small intestine, most of the absorption of nutrients occurs. The jejunum absorbs carbohydrates, fats, minerals, proteins, and vitamins. And the ileum absorbs bile acids, fluid, and vitamin B-12. The mucosa layer of the small intestine has an epithelial layer which contains many types of cells, one of which is the absorptive cells. The absorptive cells have enzymes that digest food and have microvilli that absorb nutrients. Mucosa also has villi which are fingerlike projections that increase the surface area of the epithelium which helps in nutrient absorption. After the small intestine, the material moves to the large intestine which then absorbs salts, vitamin K, vitamin B, ions, and most of the remaining water.