Digestion and Absorption


Table of Content


What is Digestion?

Digestion is a process of breakdown of complex food molecules into simple water: soluble molecules so that it can be easily absorbed by the body. Digestion is a catabolic process, that is, it is a breakdown process to release energy.

There are two types of Digestion: Mechanical Digestion and Chemical Digestion.

Mechanical Digestion involves the physical breakdown of large food molecules into small molecules. Chemical Digestion involves breakdown of complex food molecules into small molecules in presence of digestive enzyme.

Process of Digestion

What are components of Digestive System?

  • Mouth is the first part of the Digestive System where the process of digestion begins. Mouth contain glands known as Salivary Glands. These salivary glands secrete an enzyme Salivary Amylase or Ptyalin that digests the carbohydrates such as starch into maltose (simple sugar).

  • Pharynx is a part of the Digestive System as well as respiratory system. It pushes the food into the esophagus. A lid-like structure that covers the trachea or wind pipe at the time of swallowing of food is known as Epiglottis. It prevents the entry of food into the trachea. If food enters into the trachea, chocking may occur and this might also prove fatal.

  • Esophagus is also known as food: pipe that passes the food to the stomach. The process of movement of food from the esophagus to stomach is known as Peristalsis. It is a muscular process.

  • Stomach is the major part of the Digestive System where most of the digestion occurs. Stomach secretes the gastric juices which contain Hydrochloric Acid and sodium chloride. Hydrochloric Acid is secreted by gastric cells known as parietal cells. This acid is helpful in removing germs and pathogens. The environment of stomach is acidic due to hydrochloric acid. Stomach also produce an enzyme pepsinogen. Stomach also produces mucus that lubricates the stomach against hydrochloric acid.

Components of Digestive System

  • Small Intestine receives the partially digested food from the stomach. Small intestine is composed of 3 parts: Duodenum, Jejunum, Ileum. Here, carbohydrates, proteins and fats are digested. It receives the secretions from Pancreas and Liver. Some of the carbohydrates are also digested in small intestine with the help of Pancreatic Amylase.

  • Large Intestine comprises of Cecum, Colon and Rectum. Cecum receives the food from the small intestine. Colon is a part where food is digested by gut flora. Water is majorly absorbed in this part. Rectum is the part from where the undigested food reaches the anus for excretion. 


Digestion and Absorption of Carbohydrates

Digestion of carbohydrates begins in the mouth with the help of an enzyme salivary amylase. It digests the starch into maltose. Rest of the digestion of carbohydrates occurs in small intestine with the help of the enzyme pancreatic amylase secreted by pancreas. The simplest form of carbohydrates is glucose. So all the carbohydrates consumed is finally converted into glucose for absorption.


Digestion and Absorption of Proteins

Digestion of Proteins begins in the stomach. Stomach produce an enzyme Pepsinogen. Pepsinogen is an inactive form of enzyme pepsin. Inactive form of an enzyme is known as Zymogens. Pepsinogen is converted into pepsin by Hydrochloric Acid present in the stomach. Pepsin begins the process of digestion of proteins. 

Digestion of Proteins by Different Enzymes

Pancreas and Liver are two digestive glands that play an important role in the digestion. Pancreas secretes Trypsin and Chymotrypsin to digest proteins into small peptides. Other enzymes that participate in protein digestion are Carboxypeptidase and Proelastase. The simplest form of proteins is Amino acids in which they are absorbed by the body.


Describe the digestion and absorption of lipids in human beings

Liver secretes bile that helps in digestion of fats (a form of lipid). The process of digestion of fats by bile is known as Emulsification of fats. Fat digestion is also promoted by lipase enzyme from the pancreas known as Pancreatic Lipase. The simplest form of fats are Fatty Acid and Glycerol. Lipase or bile breakdown fats into fatty acids and glycerol so that they can be absorbed by the body.


Digestion of Vitamins and Minerals

Digestion of Vitamins and Minerals begins in the mouth. Further digestion of vitamins and minerals occurs in the small intestine where they are also absorbed and taken to the blood stream.


What is Appendix?

Appendix is located at the junction of the small intestine and large intestine. It is considered as a vestigial organ. Cattles use appendix for fodder digestion. It helps in digestion of food containing plant matter such as cellulose.


What is Reverse Peristalsis?

The most common example of Reverse Peristalsis is Vomiting. Medulla oblongata is the vomiting center in the brain. When it is activated due to some local irritation in the stomach, the food reverts back and results in vomiting. This is known as Reverse Peristalsis.

Diseases of the Digestive System

The common diseases of Digestive System are given below-

  • Gastroesophageal Reflux Disease (GERD) – A disease in which the ingested food leaks back from the stomach into the esophagus. It happens when the esophageal sphincter does not close well.

  • Esophagitis – The inflammation of the esophagus commonly caused by infection. It is also a complication of GERD.

  • Peptic Ulcer – A painful lesion of the stomach of small intestine.

  • Gastritis – A disease that causes the inflammation of the lining of the stomach. It has many causes such as alcohol abuse, cigarette smoking, excessive consumption of coffee and aspirin.

  • Colon Cancer –  The uncontrolled growth of abnormal cells in the large intestine. It is third most common cause of cancer in Philippines.


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