1. How the food changes consistency and form
Food is vital as it is our only source of chemical energy and must be broken down into molecules through the process of digestion. The process of digestion first occurs in the mouth by chewing or mastication, which reduces the food to a soft, flexible, and easily swallowed mass called bolus as it mixes with saliva. The presence of two enzymes in the mouth—salivary amylase and lingual lipase—initiates the breakdown of starch and dietary triglycerides, respectively. From the mouth, the bolus passes into the pharynx, esophagus, and then into the stomach. Gastric contents from the body of the stomach move into the antrum as waves of peristalsis pass over the stomach (propulsion). This continuously happens which results in the mixing of gastric contents and gastric juice. It eventually reduces to a soupy liquid called chyme. The food particles in the chyme then became small enough to fit through the narrow pyloric sphincter and thus pass into the small intestine. Mixing contractions in the small intestine mix chyme with the digestive juices and brings the food particles into contact with the mucosa for absorption. From the small intestine, chyme passes into the large intestine where it becomes solid or semi-solid due to the water absorbed, which we call feces. Feces are eliminated from the rectum to the anus by the defecation reflex.
2. How the body was able to absorb the nutrients from the foods we eat.
The body is able to absorb the nutrients from the foods we eat because the mechanical and chemical digestion that occurs from the mouth through the small intestines transforms food into monosaccharides, single amino acids, dipeptides, tripeptides, lipids, bile salts, electrolytes, vitamins, and water. These nutrients can pass through the epithelial cells lining the mucosa and into the underlying blood and lymphatic vessels via different transport processes. The large intestine also absorbs ions, such as sodium and chlorine, and some vitamins. Apart from the two, the stomach also absorbs nutrients, albeit in small amounts only as its epithelial cells are impermeable to most materials. Absorption of nutrients is vital so that the body cells can produce ATP and build body tissues.
Reference
G. J. & Derrickson, B. (2014). Principles of Anatomy and Physiology. 14th ed. New York: John Wiley & Sons, Inc.