Upper Digestive Tract

Overview of the Digestive System

  • Purpose: Prepare nutrients for absorption by the body, which can then be utilized by cells.

  • Digestion: The process of altering physical and chemical composition of food for absorption.

Digestive Tract and Accessory Organs

  • Main Organs of Upper Digestive Tract:

    • Mouth

    • Pharynx (throat)

    • Esophagus

    • Stomach

  • Lower Digestive Tract:

    • Small intestine (duodenum, jejunum, ileum)

    • Large intestine (cecum, colon, rectum, anal canal)

  • Accessory Organs:

    • Liver

    • Pancreas

    • Salivary glands

    • Gallbladder

Digestive Processes

  • Types of Secretion:

    • Endocrine: Hormones released into the bloodstream.

    • Exocrine: Secretions that travel through ducts, e.g., saliva and pancreatic enzymes.

  • Movement: Regulated peristalsis and segmentation to process food efficiently.

Physical and Chemical Digestion

  • Physical Digestion: Breaking food into smaller pieces (e.g., teeth grinding).

  • Chemical Digestion: Involves enzymes and acids that alter food chemically (e.g., saliva, stomach acid).

Structure of the GI Tract

  • Four layers of tissue in the GI tract:

    • Mucosal layer (innermost)

    • Submucosal layer

    • Muscular layer

    • Serosa (outermost)

  • Muscular Layers: Typically two layers (circular and longitudinal) except in the stomach, which has an additional layer for mixing.

Oral Cavity Structures

  • Key Structures:

    • Lips

    • Cheeks

    • Tongue: Involved in chewing and swallowing, anchored by the lingual frenulum

    • Tonsils and epiglottis (related to swallowing)

  • Salivary Glands:

    • Parotid: Largest, watery saliva with enzymes.

    • Submandibular: Enzymes and mucus.

    • Sublingual: Mucusy saliva.

Teeth Structure

  • Types of Teeth:

    • 20 baby teeth vs. 32 adult teeth

    • Central incisors, lateral incisors, canines, premolars, molars.

    • Tooth Numbering: 1 (upper wisdom tooth) to 32 (lower wisdom tooth).

  • Tooth Anatomy:

    • Pulp (core with nerves)

    • Dentin (hard tissue)

    • Cementum (connects tooth to jawbone)

    • Enamel (hardest substance in the body)

Food Movement Pathway

  • Deglutition: Act of swallowing food (bolus) from mouth through pharynx to esophagus.

  • Esophagus Length: About 10 inches with upper esophageal sphincter (UES) preventing air entry and lower esophageal sphincter (cardiac sphincter) controlling acid reflux.

Stomach Functionality

  • Sections: Fundus, body, pylorus; contains rugae for expansion.

  • Muscular Layers: Three directions for mixing (longitudinal, circular, oblique).

  • Functions: Food reservoir, liquefaction of food (chyme), secrete gastric juices, minimal absorption (some drugs, alcohol).

  • Cells in Gastric Glands:

    • Chief cells (secrete pepsin)

    • Parietal cells (secrete HCl and intrinsic factor)

    • Endocrine cells (secrete gastrin and ghrelin).

Important Digestive Terms

  • Chyme: Liquefied food mixture in the stomach.

  • Rugae: Folds in the stomach allowing expansion.

  • Gastric Juices: Help digest food and protect against microorganisms.