Digestion and Absorption

Mechanical and Chemical Digestion

Mechanical digestion breaks down food into smaller particles, and chemical digestion breaks food down even further using enzymes and acids.

There are two different types of digestive processes that take place in the body. Mechanical digestion breaks food down into smaller particles. This process increases the surface area of the food to increase its exposure to digestive enzymes. Mechanical digestion begins with chewing, or mastication, in the mouth, peristalsis in the stomach, and then segmentation in the intestines. Contractions caused by haustra mix food as it moves through the intestines. Haustra are small pouches of the colon. Taenia coli are bands of smooth muscle fibers that produce haustra of the colon. The process of mechanical digestion prepares food to be chemically digested.

Chemical digestion is a process that occurs simultaneously with mechanical digestion and involves the breaking down of macromolecules into smaller components using enzymes and acids. Enzymes are catalysts that break down food into smaller nutrient components throughout the alimentary canal, which includes the entire passageway from the mouth to the anus where food passes through. Digestive enzymes are produced and released from salivary glands, the stomach, the small intestine, and the pancreas. These enzymes include proteases, peptidases, lipases, amylases, and nucleases. Proteases and peptidases break down proteins into peptides and amino acids. Lipases break down fats. Amylases digest carbohydrates into simple sugars. Nucleases break down DNA and RNA into individual nucleotides.

Types of Digestive Enzymes

Enzyme Source Site of Release Enzyme Action
Salivary amylase Salivary glands Mouth Breaks down starch into smaller carbohydrate molecules
Gastric lipase Stomach chief cells Stomach Breaks down dietary fats into smaller molecules
Pepsin Stomach chief cells Stomach Breaks down proteins into simpler forms called peptides
Pancreatic amylase Pancreas Small intestine Breaks down starch into smaller carbohydrate molecules
Trypsin Pancreas Small intestine Breaks down proteins into simpler forms called peptides
Chymotrypsin Pancreas Small intestine Breaks down proteins into simpler forms called peptides
Carboxypeptidase Pancreas Small intestine Breaks down proteins into simpler forms called peptides
Pancreatic lipase Pancreas Small intestine Breaks down dietary fats into triglycerides and fatty acids
Nuclease Pancreas Small intestine Breaks down nucleic acids like DNA into nucleotides
Lactase Small intestine Small intestine Breaks down lactose into glucose and galactose
Maltase Small intestine Small intestine Breaks down maltose into two molecules of glucose
Sucrase Small intestine Small intestine Breaks down sucrose into two molecules of glucose