Chemical Digestion: Process and Locations

Chemical Digestion Definition and Locations

• Chemical digestion is the breakdown of large, insoluble molecules into smaller, soluble ones using enzymes, water, acids, or alkalis.
• Enzymes break down starch into maltose, which is then broken down by maltase into glucose in the small intestine.
• Chemical digestion happens in the mouth, stomach, and small intestine.

Chemical Digestion in the Mouth

• The mouth has a pH of 7.
• Saliva in the mouth contains amylase, an enzyme.
• Amylase helps break down large starch molecules into smaller maltose molecules.
• Saliva is composed of water, mucus, and amylase.

Chemical Digestion in the Stomach

• The stomach has a pH of 3.
• The acid in the stomach destroys microbes.
• Pepsin, an enzyme, begins the digestion of proteins.
• The stomach produces hydrochloric acid and provides the optimum pH for pepsin to operate.

Chemical Digestion in the Small Intestine

• Intestine adds enzymes to break down large molecules.
• Two organs that add fluid to the small intestine to aid with digestion are the pancreas and the gall bladder.
• Carbohydrates, proteins, and fats are broken down in the small intestine.
• The small intestine produces enzymes, including carbohydrase, protease, and lipase.
• The pancreas adds pancreatic juice containing alkali and all enzymes.
• The gall bladder adds bile, which contains salts to emulsify fats, and alkali.
• Alkalis neutralize stomach acid and provide an optimum pH of 8-10 for enzymes.
• Food is moved through the small intestine by peristalsis.

Absorption in the Small Intestine

• Villi are tiny structures in the small intestine that facilitate absorption.
• Villi increases the surface area for absorption.
• Soluble molecules are absorbed into the bloodstream.
• Following digestion, food passes into the blood as small, soluble molecules.

Digestion Summary

• Digestion is the breakdown of food into small, soluble molecules for absorption.
• Digestion includes both mechanical and chemical processes.
• Absorbed nutrients in blood go to the liver for growth and tissue repair or assimilation.

Large Intestine (Colon)

• Undigested food becomes waste and passes into the large intestine.
• Excess water is reabsorbed into the body, and feces is eliminated through the anus.
• The large intestine reabsorbs water, using approximately 9 liters of water daily.
• Bacteria in the gut help produce absorbable vitamins.
• Solid waste is stored in the rectum and eliminated through the anus.
• The large intestine is full of bacteria.

Key Enzymes and Their Functions

• Amylase: Breaks down starch into maltose.
• Protease: Digests proteins into amino acids.
• Lipase: Breaks down fats into fatty acids and glycerol.

Mechanical Digestion

• Teeth cuts food into smaller pieces
• Stomach grinds food by muscles contractions called peristalsis.