Digestive System Functions

Digestive System Functions

• The digestive system breaks down food into absorbable molecules.
• It absorbs these molecules for use by the body.
• The main food molecules are carbohydrates, proteins, and fats.

Digestion in the Oral Cavity

• Digestion begins in the mouth.
• Food is chewed, and enzymes in saliva start breaking down carbohydrates and fats.
• The food is swallowed, passing to the esophagus.

Stomach Digestion

• Stomach acid denatures enzymes that began digesting carbohydrates.
• Protein digestion begins in the stomach.
• Fat digestion continues.

Digestion in the Small Intestine

• Most digestion and absorption of nutrients occur in the small intestine.
• Enzymes from the pancreas are crucial for this process.
• Many pancreatic enzymes are initially inactive (proenzymes).
• Proenzymes are activated in the small intestine.
• An example of a pancreatic proenzyme is trypsinogen, which becomes trypsin.
• This conversion is catalyzed by enteropeptidase, an enzyme attached to the cell membrane of small intestine epithelial cells.
• Brush-border enzymes (on the surface of the epithelial cells) carry out further digestion of carbohydrates, proteins, and fats. Examples are sucrase, maltase, lactase.
• Carbohydrate digestion products (monosaccharides) are absorbed into the bloodstream.
• Protein digestion products (amino acids) are absorbed into the blood.
• The absorbed triglycerides combine with cholesterol and proteins to form chylomicrons.
• Chylomicrons are absorbed into lymph vessels (lacteals).
• Chylomicrons enter the venous circulation through the thoracic ducts.

Further processing

• The absorbed cholesterol is also transported in the intestines and is processed in cells