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Mechanical and Chemical Digestion

Dec 18, 2015

Digestion is the process of breaking food into its various nutrients and then the nutrients are used by the body for growth, energy and repair of cellular structures. Everything we eat and drink needs to be digested into much smaller forms before they can be absorbed by the bloodstream and before they can go to the various cells in our bodies. The process of digestion involves the breaking down of food and beverages into fat, protein, carbohydrates, and vitamins. But do you know there are two types of digestion? These are mechanical and chemical digestion.

What Are Mechanical and Chemical Digestion?

Both mechanical digestion and chemical digestion are necessary for the digestion of foods and beverages into pieces and molecules that are small enough to be absorbed in the small intestine. Both types of digestion are important and complement each other in the digestive process. There are, however, significant differences in the two types of digestion.

Mechanical digestion involves the process of physically breaking down the food into ever smaller parts. The major player in mechanical digestion is mastication, which is the act of chewing and using the teeth to break the food into pieces small enough to be swallowed into the esophagus.

  • This type of digestion generally starts and occurs in the mouth. There are also muscles in the stomach wall that contribute to mechanical digestion.
  • It can actually be seen in that you can actually see the larger food pieces turning into ever smaller pieces by the action of the teeth.

However, chemical digestion means food is broken down into small molecules by chemical energy. One big part of chemical digestion involves the enzymes located in stomach. They begin to break down food as soon as it enters the stomach.

  • Chemical digestion actually starts in the mouth when our saliva mixes in with the food. Saliva has an enzyme known as amylase that is important in breaking down carbohydrates. As an enzyme, amylase is a type of protein that undergoes a biochemical reaction to change one molecule into another molecule. Most chemical digestion, however, occurs within the stomach, with some happening in the intestines. The hydrochloric acid, located in the stomach, works for the purposes of chemical digestion.
  • Chemical digestion is completely invisible. In the process of chemical digestion, starches we eat are turned into simple sugars. Pepsin turns large proteins into peptides, which are turned into amino acids for absorption.

Specific Process of Digestion Step by Step

Mechanical and chemical digestion follows a simple pattern from the mouth through the intestinal tract. The following demonstrates the whole way that digestion actually works:

1.   Mouth

In the mouth, larger pieces of food are chewed into pieces by the teeth and by mastication. There are 32 adult teeth, each of which has a special purpose. Some grind the food; others chew the food, while still others tear apart the food we eat. The tongue is a small skeletal muscle under voluntary control. Its role is to transfer the food to the back of the mouth and to move it around, so it can be broken down. There are also the salivary glands in and around the mouth that secrete the enzymes in saliva that begin the digestive process. In the mouth, both mechanical and chemical digestion takes place.

2.   Pharynx

The pharynx is the place where food is swallowed. The pharynx is the part of the digestive tract that leads to the esophagus. The epiglottis is located within the pharynx. Its job is to close so that food doesn't enter the trachea during the act of swallowing.

3.   Esophagus

The esophagus is just the connection between the pharynx and the stomach. It has smooth muscle that contracts in order to allow the food to pass through the esophageal sphincter, which is the part of the esophagus that separates it from the environment of the stomach.

4.   Stomach

The stomach holds the food after it has passed down the esophagus. The three main roles of the stomach are to store the food prior to being digested, to secrete enzymes and hydrochloric acid so the food is more digestible, and to keep the food from dumping into the small intestines all at once.

The stomach is where chemical digestion mainly happens, especially that of protein. It does that by secreting almost two liters of hydrochloric acid daily, which contains pepsin and other liquids that are a part of the gastric fluids. The gastric fluid is highly acidic; it kills the bacteria if there are some bad ones from foods.

The stomach lining is coated with a thick type of mucus that prevents erosion of the stomach lining by the hydrochloric acid. If there is too much acid or not enough mucus, people can get gastric ulcers. Things like smoking, stress, alcohol, and heredity can contribute to getting gastric ulcers. The food remains in the stomach for at least 3-4 hours before the pyloric sphincter opens up to allow the partially digested food to enter the small intestines.

5.   Small Intestines

The small intestines are about 7 meters long and are coiled up inside the abdomen. Inside the lining of the small intestines are villi, which are small projections that increase the surface area so absorption can take place quickly. By this time, the food is broken down into its smallest form so it can be easily absorbed by the microvilli.

The small intestines are made from three parts. These include the duodenum, the jejunum, and the ileum. The duodenum takes on about 9 liters of fluid per day. The liver and pancreas play big roles in secreting substances that aid in duodenal digestion. The jejunum and ileum don't do much digestion; they are, instead, involved in absorption of the smallest food molecules.

6.   Large Intestines

The large intestine or colon takes whatever material isn't absorbed in the small intestines. There are very little nutrients in the colon; there is only undigested food material, cellulose and water left over. The colon is responsible for absorbing water from the lumen, so the stool can form.

7.   Rectum

The rectum is the last portion of the digestive system. It acts as a place to hold stool before it is finally defecated.

You can also watch the video below to know the process vividly.