The Digestive Process

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There are two types of process; mechanical process in which physically breaking the food into smaller pieces. Mechanical digestion begins in the mouth as the food is chewed. Smaller particles expose greater surface area for action by enzymes. Chemical digestion involves breaking down the food into simpler nutrients and Digestive enzymes and water are responsible for the breakdown of complex molecules such as fats, proteins, and carbohydrates into smaller molecules.

Mechanical Process in Digestion

Mechanical digestion begins in the mouth as the food is chewed. Mastication (chewing) begins the process of breaking down food into pieces small enough to be swallowed into the esophagus. Peristalsis is simply the involuntary contractions responsible for the movement of food through the esophagus and intestinal tracts.

Image showing Peristalsis is a wave of contraction of muscles of alimentary canal which pushes food down through the alimentary canal.

Image Showing Peristalsis.

Image showing Peristalsis is a wave of contraction of muscles of alimentary canal which pushes food down through the alimentary canal.

Chemical Process in Digestion

In Mouth

The digestion of starch takes place in the mouth and the saliva contains salivary amylase enzyme, which converts starch in two ways;

In Pharynx

Pharynx is place where food is swallowed and epiglottis is located within the pharynx.

In Oesophagus (Esophagus)

Food enters the esophagus and is pushed through a series of involuntary contractions called peristalsis.

In Stomach

The stomach acts as mixer and grinder with strong muscular walls, mechanically digest food while it’s acidic and enzymes work to chemically digest it. Stomach secretes hydrochloric acid daily, which contains pepsin and other liquids that are a part of the gastric fluids. Hydrochloric acid is secreted by Oxyntic (parietal) cells of the stomach wall.

Small Intestine

Chyme is thick liquid of partially digested food passed from the stomach to the small intestine. Chyme is acted upon by three main digestive juices;

  • Bile juice from the liver,

  • Pancreatic juice from the pancreas

  • Intestinal juice secreted from special cells in the intestinal epithelium at the base of intestinal villi.

The bile juice and pancreatic juice are poured into the duodenum by their respective ducts which join together to form a common hepatopancreatic duct. The intestinal juice directly mixes with the food.

Bile Juice: Bile is a yellow green watery fluid produced in the liver and transported through bile duct leading to the duodenum. Bile is devoid of enzymes. Bile contains bile pigments and bile salts.

Pancreatic Juice: Pancreatic juice is produced by pancreas. The pancreatic ducts open in the duodenum and pour their secretion there. Four enzymes contained in the pancreatic juice;

  • Trypsin: acts on proteins and converts them into polypeptides.

  • Chymotrypsin: activated form of enzyme formed by the action of trypsin on inactive chymotrypsinogen.

  • Amylase: acts on starch and complex sugars and converts them to maltose.

  • Lipase: acts on emulsified fats and converts them to fatty acids and glycerols.

Intestine Juice (Succus entericus): it contains the enzyme Erepsin, which is mainly a group of peptidases.

  • Erepsin or peptidases act on peptides and convert them to amino acids.

  • Maltose is an intestinal amylase, which converts maltose into glucose.

  • Sucrase acts on cane sugar and converts it into glucose and fructose.

  • Lactase acts on the milk sugar lactose and converts it into glucose and galactose.

  • Nucleases breakdown nucleotides into phosphate, sugar and different nitrogenous bases.

Various Digestive Enzymes Secreted and Their Role in the Digestion of Food in Humans

Table Showing Various Digestive Enzymes.
Table showing Various digestive enzymes secreted and their role in the digestion of food in humans.

Site of Secretion

Digestive juice

Enzyme

Mode of action

Mouth

Saliva

Salivary amylase (ptyalin)

Converts starch into maltose

Stomach

Gastric juice

Pepsin

Converts proteins into peptones and proteoses

Duodenum

Bile juice

No Enzyme

Emulsification of fats

Pancreatic juice

Trypsin

Converts peptones and small peptides into amino acids.

Small intestine

Intestinal juice

Erepsin

Converts peptones and small peptides into amino acids.

Sucrase

Converts sucrose into glucose and fructose.

Maltase

Converts maltose into glucose.

Lactase

Converts lactose into glucose and galactose.

Lipase

Converts fats into fatty acids and glycerols.