Chemical Digestion and Accessory Organs

Chemical Digestion

• Chemical digestion involves breaking down large food molecules into smaller molecules, allowing absorption.
• Accessory organs, like the pancreas, liver, and gallbladder, secrete substances aiding in chemical digestion, but food does not pass through them.

Learning Intentions for D4

• Students will identify and describe the functions of accessory digestive organs.
• Students will detail chemical digestion in the small intestine, including components of pancreatic fluid and their roles, bile's role in lipid digestion, and the function of carbohydrases.
• Students will explain how all four macromolecules (carbohydrates, proteins, lipids, and nucleic acids) are broken down and absorbed.

Accessory Organs

• The pancreas delivers pancreatic fluid to the duodenum. Enzymes require activation by secretions from the small intestine.
• Pancreatic fluid contains proteases (trypsin and chymotrypsin), pancreatic amylase, lipase, and bicarbonate which neutralizes stomach acid.
• Nucleases are also present.

Liver

• The liver, a major internal organ in the digestive system, produces bile.
• Bile, a greenish-yellow fluid, is composed of bile pigments (from old red blood cells) and bile salts.
• Bile salts emulsify fats, like a detergent, breaking them into smaller droplets to increase the surface area for lipase action. Emulsification is a physical process.

Gallbladder

• The gallbladder stores bile between meals.
• Fat-containing chyme stimulates gallbladder contraction, releasing bile into the duodenum.

Gastric Enzymes

• Amylases digest polysaccharides (starch). Salivary amylase and pancreatic amylase are examples.
• Carbohydrases digest simple sugars (e.g., maltose, lactase, sucrase).
• Lipases digest fats (e.g., pancreatic lipase).
• Proteases digest larger polypeptides (e.g., pancreatic protease, pepsin).
• Peptidases digest peptides into amino acids.
• Nucleases digest nucleic acids into nucleotides.
• Nucleosidases digest nucleotides into bases, sugars, and phosphates.

Digestion - Carbohydrates

• Salivary amylase starts carbohydrate digestion in the mouth.
• Further digestion occurs in the small intestine with pancreatic amylase.
• Other carbohydrases (sucrase, maltase, lactase) hydrolyze disaccharides into monosaccharides.

Carbohydrates

• Glucose is actively transported into intestinal wall cells to enter the bloodstream.

Digestion - Proteins

• Pepsin in the stomach begins protein hydrolysis, forming smaller polypeptides.
• Protein digestion primarily occurs in the small intestine (proteases, peptidases).
• Smaller peptides and amino acids are actively transported into the bloodstream.

Digestion - Lipids

• Fat arrival in the duodenum stimulates bile secretion for emulsification.
• Lipase hydrolyzes triglycerides into glycerol and fatty acids.
• Emulsification is a physical process.

Lipids

• Glycerol and fatty acids diffuse into intestinal wall cells. They are reassembled into fats and coated with proteins. These coated fats travel into lymph vessels for bloodstream entry.

Digestion/Absorption - Nucleic Acids

• Nucleases break down nucleic acids into nucleotides in the small intestine.
• Nucleosidases further break down nucleotides into sugars, nitrogen bases, and phosphates.
• These are actively transported into intestinal epithelial cells then into the bloodstream.

Check Your Understanding

• Understand the function of accessory organs and their role in both physical and chemical digestion.
• Explain the breakdown and absorption of the four macromolecules (carbohydrates, proteins, lipids, and nucleic acids).

Did You Know?

• Babies produce lipase in salivary glands and stomach to facilitate milk fat digestion.
• Ingesting a whole protein can trigger an allergic response.
• The average person produces about 500 ml of intestinal gas daily.

Assignment/Videos

• Video link included: https://www.youtube.com/watch?v=nM5kMSjBrmw
• Chemical digestion chart booklet and Digestion review are also assigned.

This quiz covers the intricate process of chemical digestion, focusing on the role of accessory digestive organs such as the pancreas, liver, and gallbladder. Students will explore how various enzymes facilitate the breakdown of macromolecules in the small intestine. Test your understanding of the components involved in digestive processes.