A&P II Module 8: The Digestive System (Part 2)

Module Overview

• Focus on the Digestive System, specifically between Chapters 23.5-23.7.

In-Class Activity #1

What is the function of the digestive system?

1. Break down food

2. Release nutrients from food

3. Absorb nutrients

Learning Outcomes

1. Trace the Flow of Food: Understand the entire journey food takes from ingestion to excretion.

2. Accessory Organs' Role in Digestion: Identify how organs like the liver, pancreas, and gallbladder contribute to digestion in the small intestine.

3. Chemical Digestion Locations and Secretions: Recognize where chemical digestion of carbohydrates, proteins, lipids, and nucleic acids occurs, along with the secretions involved.

4. Absorption Mechanisms: Discuss how digested food molecules are absorbed into the body.

1. Flow of Food from Mouth to Anus

• Pathway: Mouth → Oral cavity → Tongue → Pharynx → Esophagus → Stomach → Small Intestine (Duodenum → Jejunum → Ileum) → Large Intestine (Cecum → Colon → Rectum → Anus)

• Chyme Formation: Chyme from the stomach enters the small intestine where digestion and absorption primarily occurs.

In-Class Activity #2

Of the alimentary canal organs, which 2 play the biggest role in digestion?

Small intestine and stomach

Of the alimentary canal organs, which plays the biggest role in absorption?

Small intestine

2. Digestion in the Small Intestine

• Mechanical Digestion:

  • Segmentation: Smooth muscle contractions mix chyme with digestive juices; increases nutrient absorption by pushing food against the mucosa.

  • Migrating Motility Complex: Movements that help push the chyme through the intestines.

• Chemical Digestion:

  • Proteins and Carbohydrates: Digestion completed in the small intestine, aided by intestinal and pancreatic juices.

  • Lipids: Primarily digested in the small intestine, facilitated by bile and lipase from the pancreas.

3. Digestion in the Large Intestine

• Functions: Finishes absorption of nutrients & water, synthesizes vitamins, and forms feces.

• Bacterial Flora: Promote digestion and absorption, synthesize vitamins.

• Differences from Small Intestine:

  • Lacks circular folds and villi; has simple columnar epithelium.

  • Contains goblet cells for mucus secretion and absorptive cells.

4. Accessory Digestive Organs

• Liver: Produces bile, which emulsifies lipids for absorption.

• Pancreas: Secretes pancreatic juice containing enzymes for digestion (e.g., amylase, lipase, nuclease).

• Gallbladder: Stores and releases bile into the small intestine.

In-Class Activity #3

State the 4 macro-molecules and their respective building blocks.

1. Carbs = Monosaccharides

2. Proteins = Amino Acids

3. Lipids = Fatty Acids

4. Nucleic Acids = Nucleotides

5. Chemical Digestion of Macromolecules

• Carbohydrates:

  • Digested by salivary and pancreatic amylase into disaccharides, further broken down into monosaccharides by maltase, sucrase, and lactase.

• Proteins:

  • Initiated in the stomach (HCl and pepsin), continued in the small intestine by pancreatic enzymes.

• Lipids:

  • Digested significantly by pancreatic lipase. Minor contributions from lingual and gastric lipases occur.

• Nucleic Acids:

  • Broken down in the small intestine by pancreatic nucleases and further by nucleosidase and phosphatase.

6. Absorption of Nutrients

• Water Absorption:

  • Small intestine absorbs around 90% of ingested water; large intestine absorbs most of the rest.

• Absorption Mechanisms:

  • Active Transport: Requires energy to move molecules; e.g., glucose and amino acids.

  • Passive Diffusion: No energy required; e.g., short-chain fatty acids.

  • Facilitated Diffusion: Uses transport proteins; e.g., fructose.

  • Co-transport: Molecules move together with sodium ions; e.g., glucose, amino acids.

  • Endocytosis: Engulfing of molecules by cells, less common in digestion.

7. Types of Absorbed Food Substances

In-Class Activity #4

Explain the role of amylases, proteases, and lipases in digestion.

1. Amylases =

2. Proteases =

3. Lipases =

8. Take Home Points

1. Most digestion and absorption occur in the small intestine.

2. The large intestine focuses on water reabsorption and feces formation.

3. The liver secretes bile, the pancreas produces pancreatic juice, and the gallbladder functions to aid in digestion.

4. Macromolecules are broken down into building blocks for absorption in the small intestine.

5. Absorption occurs through various mechanisms and is transported to the liver or systemic circulation.