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How the food changes consistency and form
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How the body was able to absorb the nutrients from the foods we eat.
Whenever we introduce external elements like food to our bodies, it always undergoes a series of mechanisms and processes. When food is taken up, it is processed, broken down and absorbed through the help of our digestive system or gastrointestinal tract. Now, let us discuss how food undergoes this process and how we are able to absorb the nutrients it has for our bodies to use and work on for.
The food journey all starts with the oral cavity or the mouth. When food enters the mouth, it undergoes processes of mechanical (chewing) and chemical (hydrolysis) digestion. As food is being chewed or hydrolyzed, it turns into a sphere of digested food called bolus which then is swallowed to travel to the esophagus. Once food becomes bolus, its consistency changes from being roughly solid, bits-to-pieces into a smooth, semi-digested bolus that passes through the esophagus. The esophagus mainly transfers or propels the bolus from the mouth to the stomach where it is then churned and hydrolyzed to be broken down even further or simply to store it if it is not yet ready to be passed on to the succeeding structure. Once bolus is digested in the stomach, it turns into a fluid and melted type of a substance now called the chyme. The chyme will now travel to the next part of the GI tract which is the small intestine. Here, the nutrients digested from the food taken up are finally going to get absorbed which is also facilitated with more enzymatic digestion to have more nutrients and minerals absorbed from the processed food substance. Nutrients such as carbohydrates, proteins, and lipids are absorbed in the small intestines via transport processes of either active transport, diffusion, and pinocytosis between the submucosa layer of the GI tract and the blood. After all the absorption and hydrolysis from the small intestine, the food substance then moves to the large intestine or the colon. Food is still being processed here for absorption but not of nutrients but mostly for ions and water. Once done, the food material is no longer nutrient-filled and can already be regarded as waste. This is when this waste is transferred and stored to the rectum. This serves as the storage of the waste material now known as feces as it waits for a stimulus that will grant its expulsion outside of the GI tract. Once the stimulus is received, the feces move out of the rectum via the anus and into the external environment of the body.
Reference: Tortora GJ & Derrickson B. (2014). Principles of Anatomy and Physiology. John Wiley & Sons, Inc. 14 edition.