Digestive System Flashcards

Digestive System

Introduction

The digestive system's main function is to break down food into chemicals that the body can use. This process starts in the mouth with chewing.

In the stomach, food mixes with acids and enzymes, further breaking it down for absorption in the small intestine. Fiber is essential for intestinal movement, while gut bacteria produce vitamin K and short-chain fatty acids.

Learning Objectives

1. Structure and Function: Understand the makeup and roles of digestive organs and accessory organs.

2. Digestion Processes: Define digestion and list enzymes and secretions per organ.

3. Gastrointestinal Movements: Define the various movements.

4. GI Tract Wall Layers: Explain the layers.

Organs of the Digestive System

The digestive system consists of:

• Gastrointestinal (GI) Tract Organs: A continuous tube from the mouth to the anus. Includes the mouth, pharynx (throat), esophagus, stomach (underneath the pancreas), small intestine, large intestine, and anus.

• Accessory Digestive Organs: Aid GI tract organs. Includes teeth, tongue, salivary glands, liver, pancreas, and gallbladder.

The GI Tract

Food and fluids enter through the mouth, are digested, and nutrients are absorbed into the body. The GI tract is open to the external environment, so its contents are technically outside the body until absorption occurs.

Accessory Digestive Organs

These organs facilitate digestion:

• Teeth and Tongue: Physically break down food and aid swallowing.

• Salivary Glands, Liver, and Pancreas: Produce secretions (enzymes, hormones) for chemical breakdown.

• Gallbladder: Stores and secretes bile (produced by the liver) into the small intestine.

Digestive Functions: Six Processes

1. Ingestion: Taking food/liquids into the mouth.

2. Secretion: Producing and releasing substances that aid digestion and movement of contents.

   • Secretions include water, hydrochloric acid (HCl), salts, and buffers.

3. Propulsion: Muscular contractions mixing and moving contents.

4. Digestion: Breaking food into smaller molecules.

   • Mechanical Digestion: Physical breakdown (e.g., chewing).

   • Chemical Digestion: Enzymes and acids dissolving food.

5. Absorption: Nutrients moving from the lumen into blood/lymph.

6. Defecation: Eliminating undigested material, waste, bacteria, and sloughed-off cells.

Organ-Specific Functions

• Ingestion: Only occurs in the mouth.

• Defecation: Only occurs in the anus.

Other processes involve multiple organs:

• Mechanical Digestion: Mouth (chewing), stomach (churning), intestines (segmentation).

• Propulsion: Oropharynx, esophagus, stomach, intestines (peristalsis).

• Chemical Digestion: Mouth, stomach, intestines.

• Absorption: Primarily small and large intestines.

GI Tract Wall Structure

The GI tract wall (esophagus to anal canal) has four layers (tunics):

1. Mucosa: Innermost layer surrounding the lumen (the passage for food/fluids).

2. **Submucosa

3. **Muscularis

4. **Serosa.

Each layer consists of sublayers.

Histological Features

The lumen of the small intestine is not round. It contains finger-like projections that increase surface area. Higher surface area means increased secretion, digestion, and absorption.

• Mucosa: Epithelial cells with red nuclei are visible near the lumen.

• Submucosa: Stains white.

• Muscularis Externa: Stains orange.

• Serosa: Very thin outer layer.

Detailed Layer Breakdown

1. Mucosa:

   • Innermost layer.

   • Epithelium, connective tissue, thin smooth muscle.

   • Simple columnar epithelium (most of the tract).

   • Functions: secretion (mucus, enzymes, hormones), absorption, protection against disease.

2. Submucosa:

   • Areolar connective tissue.

   • Rich in blood and lymphatic vessels.

   • Contains nerve fibers and glands.

   • Connects mucosa to muscularis.

3. Muscularis:

   • Deep to the submucosa, made of smooth muscle.

   • Inner circular layer and outer longitudinal layer.

   • Exceptions: Mouth, pharynx, upper esophagus, and anus have skeletal muscle for voluntary control.

   • Responsible for movement and mixing. Contains the myenteric nerve plexus.

   • Sphincters: Thickenings that control opening/closing.

4. Serosa:

   • Outermost layer; visceral peritoneum.

   • Connective tissue and simple squamous epithelium.

   • Attaches GI tract organs to surrounding structures.

   • Secretes serous fluid to reduce friction.

This the basic structure of the gastrointestinal tract wall.