Chapter 19-Digestive System

Chapter 19.1-19.2: Digestive System Overview

Organ Systems

1) Gastointestinal (GI) Tract- Alimentary Canal: continuous tube extending from

mouth to anus- Mouth, pharynx, esophagus, stomach, sm.

intestines, lg. intestines- About 5-7 meters (16-23ft) long

2) Accessory Organs- Aid in the physical and chemical breakdown of food- Teeth, tongue, salivary glands, liver, gallbladder,

pancreas

Basic Functions

1) Ingestion: taking in food

2) Secretion: release ≈ 7 liters of water, acid, buffers, enzymes

3) Mixing and Propulsion: contraction/relaxation of smooth muscle pushes food/secretion mixture down GI tract

Basic Functions

4) Digestion: mechanical and chemical

5) Absorption: entrance of fluids, ions, and small molecules into the lining cells of GI Tract

6) Defecation: any non-absorbed material eliminated from body

Four Layers

1) Mucosa- Inner epithelium of GI tract

2) Submucosa- Connective tissue- Contains blood and nerve supply

3) Muscularis- Thick layer of muscle

4) Serosa - Outer layer- Simple squamous epithelium

SUBMUCOSA

MUSCULARIS

SEROSA

MUCOSA

Chapter 19.3-Mouth

Oral Cavity

- Formed by the cheeks, hard and soft palates, and tongue

- Hard palate: roof of the mouth- Soft palate: back of the mouth, including the uvula

- Tongue: accessory organ composed of skeletal muscle covered by a mucous membrane

- Lingual frenulum: a folded membrane in the midline of the undersurface that limits movement

- Papillae: small projections on the upper surface and sides

Lingual frenulum

Hard palate

Soft palateUvula

Salivary Glands

- Three pairs (accessory organs) that lie outside oral cavity- Release saliva into ducts emptying into oral cavity

1) Parotid glands2) Submandibular glands3) Sublingual glands

- Saliva = 99.5% water and 0.5% solutes- Lubricates food- Salivary amylase begins digestion of starches in mouth

Anatomy of Teeth

- Accessory organs located in bony sockets of mandible and maxillae

- Three major external regions:1) Crown2) Neck3) Root

- Majority of tooth made up of dentin- Calcified connective tissue- Crown covered in enamel- Root covered in cementum

CROWN

NECK

ROOT

Enamel

Dentin

Cementum

Anatomy of Teeth

- Dentin encloses the pulp cavity- Connective tissue containing blood/lymphatic

vessels and nerves- Extends into root canals CROWN

NECK

ROOT

Enamel

Dentin

Cementum

Pulp in pulp cavity

Root canal

Types of Teeth

- Deciduous (20) vs. Permanent (32)

- Incisors- Closest to midline- Used for cutting into food

- Cuspids (canines)- One pointed cusp used for tearing and shredding

- Premolars and molars- Crushing and grinding food

Deciduous

Permanent

Digestion in the Mouth

- Mechanical digestion of food begins in the mouth- Mastication: chewing and mixing of food into bolus

- Salivary amylase begins breaking down carbohydrates- Polysaccharides (starch and glycogen)- Disaccharides (maltose)- Monosaccharides (glucose, fructose)

Bolus

Chapter 19.4: Pharynx and Esophagus

Esophagus

Oropharynx

Laryngopharynx

Pharynx

- A funnel shaped tube composed of skeletal muscle and mucous membrane

- Food travels from mouth -> oropharynx -> laryngopharynx -> esophagus

Esophagus

- Muscular tube lined with stratified squamous epithelium

- Connects the laryngopharynx to the superior part of the stomach- Controls food transport using muscular contraction and sphincters

- Upper esophageal sphincter (UES)- Regulates movement of food into esophagus

- Lower esophageal sphincter (LES) - Regulates movement of food into stomach

Three Stages of Swallowing

1) Voluntary stage- Movement from mouth to pharynx

2) Pharyngeal stage- Esophageal sphincter relaxes and food moves into

esophagus- Breathing interrupted

3) Esophageal stage- Food pushed through esophagus: peristalsis