1. How the food changes consistency and form
Food undergoes physical and chemical changes as it travels through the digestive system. The food is ingested into the mouth for chewing or mastication, in which it is rolled by the tongue, sliced by the teeth, and dissolved with saliva. Certain enzymes like salivary amylase and lingual lipase then break down starch and fats into smaller molecules. This turns the food into a soft and flexible mass called bolus. The food then moves from the mouth, pharynx, and esophagus to the stomach through swallowing or deglutition. The muscles in the stomach contract to churn food, while specialized cells in the stomach secrete gastric juices such as HCl, pepsin, intrinsic factors, and gastric lipase. These gastric juices turn bolus into a semi-fluid mass of partly digested food called chyme, which then enters the small intestines. In the small intestines, chyme is physically digested through segmentation and a type of peristalsis called migrating motility complex. The intestinal juices, pancreatic juices from the pancreas, and bile from liver and gallbladder also chemically digest the food. Meanwhile, the absorptive cells of the small intestine absorb most nutrients and 90% of the water from chyme. Chyme then enters the large intestine, where nutrients and further absorbed until it becomes a semisolid substance called feces. Feces is then temporarily stored in the rectum and eventually released out of the anus through a process called defecation.
2. How the body was able to absorb the nutrients from the foods we eat
Absorption is the passage of digested nutrients from the GI tract into the blood or lymph. Around 90% of all absorption of nutrients and water occurs in the small intestine. The remaining 10% occurs in the stomach and large intestine. Undigested or unabsorbed material in the small intestine is passed on to the large intestine. The absorptive cells in the small and large intestines absorb nutrients and water from the food we eat
References:
Tortora, G. J., & Derrickson, B. (2011). Principles of anatomy and physiology (13th ed). John Wiley & Sons.