Digestive System Functions and Processes

Digestive System Functions

• The digestive system breaks down food mechanically and enzymatically, absorbing usable molecules.
• Key food types include carbohydrates (poly- and disaccharides), proteins (amino acids), and fats (triglycerides, cholesterol).

Digestion Begins in the Oral Cavity

• Digestion starts in the mouth, where food is chewed and enzymes in saliva begin breaking down carbohydrates and fats.
• Chewing mechanically breaks down food.
• Saliva contains enzymes for carbohydrate and fat digestion.
• Swallowing moves food to the esophagus.

Stomach Digestion

• Stomach acid continues digestion, primarily proteins, while denaturing carbohydrate-digesting enzymes.
• This means that further carbohydrate digestion temporarily stops once food enters the stomach.

Small Intestine Digestion

• The small intestine is the main site for digestion and absorption.
• Most digestive enzymes come from the pancreas (in an inactive form).
• Pancreatic enzymes are activated in the small intestine.
• Enzymes (activated from inactive proenzymes) are critical for proper digestion.
• Brush-border enzymes, located on the cell membranes of the small intestine, further digest macromolecules.
  • Examples: sucrase, maltase, lactase to digest sugars, and others.

Absorption in the Small Intestine

• Monosaccharides (glucose, fructose, galactose) are absorbed into the bloodstream after carbohydrate digestion.
• Proteins are broken down to amino acids and small peptides, also absorbed into the bloodstream.
• Triglycerides and long-chain fatty acids are broken down, enabling absorption across the intestinal cell membrane.
• Monoglycerides and free fatty acids then recombine into triglycerides within the epithelial cells.
• These fats, combined with cholesterol and proteins, form chylomicrons.
• Chylomicrons are released into lymphatic vessels (lacteals).
• Chylomicrons eventually enter the bloodstream through the thoracic duct.