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How does the food change in consistency and form?
The digestive system is responsible for the breakdown of food, as well as the absorption of nutrients present in the substances we consume. The moment that we ingest food and/or liquids, different processes already occur in the mouth to digest substances both chemically and mechanically. First, through chewing, large pieces of food are broken down into smaller portions for easier digestion as we go along the digestive pathway. Next, enzymes present in saliva, such as amylase and lipase, further break down starch and lipids into maltose and fatty acids respectively. At this point, food is now known as bolus, and will eventually be pushed towards the pharynx or throat, and into the esophagus where peristalsis occurs to continually break down food. Next, as the bolus enters the stomach, gastric juices and digestive enzymes further digest food to turn it into chyme. Chyme is then transported by the stomach into the small intestine to effectively absorb the nutrients from the broken down food. As chyme continues its journey in the intestines, it transitions into a more solid substance due to the absorption of water. This is referred to as feces, and shall be expelled through the anus.
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How could the body absorb the nutrients from the foods we eat?
Majority of the nutrients obtained from the food we eat are absorbed by the body through the small intestine, though other organs, such as the stomach and large intestine, still play crucial roles in this endeavor.
Stomach.
The stomach, particularly its mucous cells, absorb a few substances and, hence, deliver these nutrients to the bloodstream. These substances include relatively small amounts of water, ions, short-chain fatty acids, and certain drugs.
Small Intestine.
This digestive organ accounts for 90% of the total absorption of nutrients and water. Absorptive cells, villi, and microvilli present in the small intestine’s environment enable it to digest and absorb the nutrients, ions, and substances present in chyme. Moreover, intestinal and pancreatic juices, enzymes, and bile further aid the organ to chemically break down food.
Large Intestine.
The mucosa of the large intestine enables it to absorb water, as well as some ions and vitamins. Moreover, the action of the large intestine contributes to water balance, as well as the solidification of feces as it is headed for expulsion.