Digestive_system_II_F2020

Oral Structures

General Overview

• The oral cavity comprises several structures including:

  • Hard Palate

  • Soft Palate

  • Tongue

  • Teeth

  • Lips

  • Cheeks

Food Disassembly

• Involves two main processes:

  • Mechanical: Physical breakdown of food.

  • Chemical: Involves enzymes from salivary glands.

Oral Cavity

Lining and Structure

• Lined by stratified squamous epithelium.

• Palate: A partition that separates the respiratory and digestive passages.

  1. Hard Palate:

     • Made up of palatine, maxillary, and incisive bones.

     • Provides a hard surface for the tongue to mash food.

  2. Soft Palate:

     • Composed of muscles; closes off the passage to the nasal cavity during swallowing.

Tongue

Functions

• Manipulation of Food: Aids in prehension (grasping), grooming, and deglutition (swallowing).

• Muscular organ that occupies the oral cavity.

• Special adaptations in different species:

  • Dog: Aids in temperature control.

  • Ox: Prehensile structure for gathering grass.

  • Cat: Unique structure for grooming.

Teeth

Role in Digestion

• Principal function is mastication (chewing).

• Helps in food gathering and serves as weapons in some species.

  • Types of Teeth:

    • Brachyodont: Low-crowned teeth, found in humans, carnivores, pigs, and ruminant incisors.

    • Hypsoodont: High-crowned and ever-growing, found in permanent horse teeth and ruminant cheek teeth.

Anatomy of Teeth

• Crown: Visible part above the gum line.

• Neck: Area where the crown meets the root, usually covered by gums.

• Root: Anchoring portion within the jaw.

Types of Teeth

Incisors

• Central, intermediate, and corner categories.

• Primarily used for grasping and nibbling.

Canines

• Sharp teeth for ripping and tearing.

Premolars & Molars

• Found in both upper and lower dental arches.

• Upper Arcade:

  • Contains incisive bone for incisors and maxillary bone for canines, premolars, and molars.

• Lower Arcade:

  • Mandible supports incisors, canines, premolars, and molars.

Lips and Cheeks

Structure

• Composed of stratified squamous epithelium.

• The core consists of fibroelastic tissue and skeletal muscles.

• Anatomy:

  • Integumentary Layer: Contains dermis and hypodermis.

  • Mucosal Layer: Lines the interior part of the lips and cheeks.

Salivary Glands

Types and Functions

• Include:

  • Parotid: Located ventral to the ear, primary salivary gland.

  • Zygomatic: Located ventral to the eye.

  • Mandibular: Located caudally to the angle of the mandible.

  • Sublingual: Nearby the tongue.

• Secretions:

  • Can be serous, mucous, or mixed.

• Functions include:

  • Production of enzymes like salivary amylase and lipase.

  • Moistening and lubrication of ingested food.

Pharynx

Regions

• Divided into three main sections:

  • Oropharynx: Located below the soft palate and caudal to the oral cavity.

  • Nasopharynx: Above the soft palate, caudal to the nasal cavity.

  • Laryngopharynx: Above the larynx.

Functions

• Acts as a common passageway for the respiratory and digestive systems.

• Connects the nasal and oral cavities to the trachea and esophagus, directing air and food intake appropriately.

Esophagus

Structure and Function

• A highly muscular tube leading from the laryngopharynx to the stomach.

• Muscles: Skeletal near the cranial end and smooth near the caudal end.

• Strcuture:

  • Pierces the diaphragm to connect to the stomach.

  • Lined with stratified squamous epithelium.

Stomach

General Characteristics

• Serves as a dilation within the GI tract located caudal to the esophagus.

• Types include:

  • Simple Stomach: Single compartment found in carnivores, horses, and pigs.

  • Complex Stomach: Four compartments found in ruminants.

Functions

• Produces gastric juice for digestion.

• Mechanically mixes and breaks down food using muscular walls.

• Involved in peristalsis to move food to the duodenum.

• Lined by simple columnar epithelium, providing mucus secretion.

Stomach Anatomy

Layers of the Stomach Wall

• Tunica:

  • Consists of four layers: Mucosa, Submucosa, Muscularis, and Serosa.

• Mucosa Components:

  • Contains glandular epithelium and gastric pits.

  • Cell Types:

    • Cuboidal Neck Cells: Secrete mucus.

    • Chief Cells: Secrete gastric enzymes (pepsin, rennin, gastric lipase).

    • Parietal Cells: Secrete hydrochloric acid (HCl).

Muscular Layers

• Muscularis Tunic:

  • Contains three layers of smooth muscles:

    1. Outer Longitudinal Layer: Continuous with esophagus and duodenum.

    2. Middle Circular Layer: Forms sphincters.

    3. Inner Oblique Layer: Additional layer for enhanced mixing.

Gastric Functionality

• Gastric folds allow for expansion of the stomach during meals, enhancing its ability to accommodate large volumes of ingested material.