Digestion_2024W1-POST

Lesson Outline: The Digestive System

  • Functions and Development

  • Regions of the Digestive System

    • Buccal Cavity and Pharynx

    • Alimentary Canal

      • Esophagus

      • Stomach

      • Intestines

Components of the Digestive System

  • References for Digestion Lectures:

    • Chapter 13 – The Digestive System

      • 5th Edition: Pages 497-528

      • 6th Edition: Pages 504-535

      • 7th Edition: Pages 504-535

  • Main Functions of the Digestive System:

    • Analyze structural differences in vertebrate digestive tracts affecting nutrient absorption.

    • Consider the quality of food and the basic digestion processes:

      • Ingestion

      • Storage

      • Mechanical Digestion

      • Chemical Digestion

      • Microbial Digestion

      • Absorption

      • Water Reabsorption

      • Defecation

    • Predict diet based on digestive tract structure or vice versa.

Digestive System - Basic Structure

  • The adult digestive tract is a hollow passage from mouth to anus or cloacal opening.

Processes of Digestion

  1. Ingestion

  2. Food Storage

  3. Mechanical Digestion

  4. Chemical Digestion

  5. Microbial Digestion

  6. Absorption

  7. Water Reabsorption

  8. Defecation

Diets of Animals

  • General diets include:

    • Carnivores (other animals)

    • Herbivores (plants)

    • Omnivores (combination of everything)

    • Detritivores (dead organic material)

    • Parasitic feeders (blood and plant fluids)

  • Considerations:

    • Importance of different digestive tract regions varies with diet.

Quality of Food

  • Morphology of digestive tract regions reflects food quality:

    • Higher quality foods release more energy with less time and energy required for digestion.

    • Example Diet Ranking:

      • High Quality: Fish

      • Medium Quality: Blood

      • Low Quality: Leaves

Digestive System Problem 1

  • Rank diets based on quality.

  • Consider giraffes (leaves) and parasitic lampreys (blood) - which has higher quality diet?

Primary Regions of the Digestive System

  1. Buccal Cavity

    • Site of ingestion, structures for feeding and swallowing.

    • The tongue propels food to pharynx.

    • Chemoreceptors for taste.

  2. Saliva in the Buccal Cavity

    • Contains mucus, digestive enzymes, toxins, anti-coagulants.

The Digestive System - Teeth

  • Types of Teeth:

    • Enamel: hardest substance in body, high mineral content.

    • Dentin: bone-like, continuously deposited.

    • Cementum: anchors root to socket.

    • Teeth Forms:

      • Pleurodont (medial bone attachment)

      • Polyphyodont (continuous replacement)

      • Diphydont (two sets of teeth)

      • Thecodont (teeth in sockets)

Digestive System - Teeth Functions

  • Sharp teeth for cutting and puncturing.

  • Different teeth serve various functions:

    • Incisors: cutting

    • Canines: puncturing

    • Premolars/Molars: grinding

Pharynx and Esophagus

  • Pharynx:

    • Located posterior to the buccal cavity; prevents food entering larynx.

  • Esophagus:

    • Muscular tube transporting food to stomach; birds have a crop for storage.

Stomach Functions

  • Stores food, adds enzymes/acid, mechanically churns food.

  • Types of Stomach:

    • Mono-gastric with single chamber is common.

Digestive System Problem 2

  • Identify alimentary canals from vertebrates based on diet (e.g., perch, lungfish, lamprey).

Specialized Stomachs

  • Proventriculus and Gizzard:

    • Proventriculus: produces acid and enzymes.

    • Gizzard: specialized grinding stomach, sometimes uses stones for grinding.

Intestinal Functions

  • Main site for chemical digestion of macromolecules.

  • Duodenum:

    • Receives bile and digestive enzymes.

Adaptations of the Small Intestine

  • Plicae (circular folds), villi, and microvilli increase absorption surface area.

Alimentary Canal - Caecum

  • Caecum:

    • Blind-ending chamber specialized for cellulose fermentation, containing microorganisms.

Large Intestine Functions

  • Water reabsorption and feces consolidation.

  • Larger in terrestrial than aquatic vertebrates.

Digestive System Problem 4

  • Compare RG and GC regarding digestive differences based on dietary needs.