Food acts as a source of energy for human beings. It consists of major components like carbohydrates, proteins, and fats. The natural form of these major components cannot be digested by human beings. So, these complex components like carbohydrates, proteins, and fats are converted into simpler molecules by the process which is called digestion. Indigestion, different types of digestive enzymes and gastrointestinal hormones are present, which play an important role in converting the complex substances into simpler substances. Let us take an overview of the digestive enzymes and gastrointestinal hormones and their role in digestion.
Digestion is achieved by different mechanical and chemical processes. The mechanical processes of digestion are accomplished by the buccal cavity. The two main functions of the buccal cavity are as follows:
- Food mastication – It can be achieved with the help of teeth, tongue, and saliva.
- Lubrication of food – Masticated food substances is converted into the bolus with the help of saliva, which lubricates the food substances.
Chemical processes are achieved by the following enzymes and hormones.
Salivary amylases and lysozymes
These enzymes are produced by the oral cavity. The main function of these enzymes is to split the carbohydrates by the hydrolytic actions. The function of these enzymes are as follows:
- Salivary amylases – 30% of starch molecules are converted into maltose by salivary amylases at the pH of 6.8.
- Lysozymes – It acts against the bacterial infections. They are also called antibacterial agents.
Gastric glands are present in the mucosa of the stomach. The following types of cell are present in the gastric gland.
- Mucous neck cells – These cells secrete mucus, which is used to protect the mucosal epithelium from concentrated HCl. This concentrated HCl is secreted by the oxyntic cells.
- Peptic or chief cells – These cells secrete the proenzyme pepsinogen. It is in an inactive form. This inactive proenzyme pepsinogen is activated by the chyme and converted into the active form of the enzyme which is called pepsin. Pepsin is used to convert the proteins into proteoses and peptones.
- Parietal or oxyntic cells – These cells secrete concentrated HCl and intrinsic factor. Intrinsic factor plays an important role in the absorption of the vitamin B12.HCL is used to activate the proenzyme pepsinogen.
Finally, the following enzymes are secreted by gastric glands:
- Pepsin – It is used to denature the proteins into peptones and proteases.
- Rennin – It is a type of proteolytic enzyme which is present in the infant’s gastric juice.
- Lipase – Small amount of lipase enzyme is secreted by the gastric gland. It is used to convert the di and monoglycerides into fatty acids and glycerol.
Small intestine enzymes
In the small intestine, three major digestive juices are secreted. These are as follows:
- Bile juice
- Pancreatic juice
- Intestinal juice
Bile juice is secreted by the liver. It is a yellowish color fluid. The main function of bile juice is to digest the lipid molecules and to activate the lipase enzymes. Bile juice consists of the following components:
- Bilirubin and biliverdin
- Bile salts
Bile juice helps to break down the lipid molecules into di-and monoglycerides by the lipase enzymes.
The pancreatic juices are secreted by the pancreas. Pancreatic juice consists of the following inactive enzymes. These enzymes are activated by the intestinal mucosal secretions.
- Trypsinogen – An inactive form of trypsinogen is converted into an active form, trypsin by enteropeptidase (one of the intestinal mucosa secretion). Trypsin is used to convert the protein molecules into dipeptides.
- Chymotrypsinogen – An inactive form of chymotrypsinogen is converted into an active form, chymotrypsin. Proteins are denatured into dipeptides by chymotrypsin.
- Procarboxypeptidases – An Inactive form of procarboxypeptidase is converted into an active form, carboxypeptidase. Carboxypeptidase is also used to denature the protein.
- Amylases – Amylases are used to denature the polysaccharides into the disaccharides.
- Lipases – Lipases are used to convert the fats into diglycerides and monoglycerides.
- Nucleases – Nucleases are used to convert the nucleic acids into nucleotides and nucleosides.
The Intestinal mucous epithelium of the small intestine consists of the following:
- Brush border cells.
- Goblet cells.
The secretions of brush border cells and goblet cells from the intestinal juice in the small intestine. Intestinal juice consists of the following enzymes:
- Disaccharidases – It is also called maltases. Maltases are used to convert the maltose into glucose.
- Dipeptidases – These enzymes are used to convert the dipeptides into simple amino acids.
- Lipases – Lipases are used to convert the diglycerides and monoglycerides into fatty acids and glycerols.
- Nucleosidases – These enzymes are used to convert the nucleotides into nucleosides, sugars, and bases.
- Lactases – Lactases are used to convert the lactose into simple glucose.
Along with digestive enzymes, hormones also play an important role in the digestion.
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