Digestive System Overview

Introduction

• Focus on the digestive system from mouth to stomach.
• Videos on absorption are available separately.
• Overview of digestive system processes, functions, and organs.

Key Digestive Processes

1. Ingestion
   • Begins in the mouth with teeth, tongue, and saliva.
   • Mechanical and chemical digestion starts here.
2. Digestion
   • Main site: stomach.
   • Mechanical digestion: mouth and stomach.
   • Chemical digestion: mouth, stomach, duodenum (start of small intestine).
3. Absorption
   • Takes place in the intestines, mainly small intestines.
   • Nutrients follow specific pathways into the blood.
4. Assimilation
   • Nutrients become part of tissues (separate video available).
5. Egestion
   • Removal of undigested food via defecation.
   • Not to be confused with metabolic waste.

Structure and Function: Teeth

• Total 32 adult teeth, including wisdom teeth.
• Types of teeth:
  • Incisors: Cutting, located at the front.
  • Canines: Tearing, reduced size in humans.
  • Premolars: Smaller grinding teeth.
  • Molars: Heavy grinding, strongest bite force.
• Purpose:
  • Break food into smaller pieces.
  • Increase surface area for faster enzyme action.

Accessory Structures for Chewing and Swallowing

• Salivary Glands
  • Parotid Gland: Largest, under the ear.
  • Sublingual Gland: Under the tongue.
  • Submandibular Gland: In the lower jaw.
• Tongue
  • Mixes food and forms it into a bolus.

Swallowing and Esophagus

• Pharynx: Passage for food into esophagus.
• Epiglottis: Flap preventing food from entering airways.
• Esophagus
  • Made of smooth muscle.
  • Moves food via peristalsis (wave-like contractions).
  • Lined with goblet cells secreting mucus.

Stomach

• Sphincter Muscles
  • Cardiac sphincter: Entrance, prevents backflow.
  • Pyloric sphincter: Exit, regulates passage to small intestine.
• Digestion
  • Mechanical: Churning and mixing via stomach wall contraction.
  • Chemical: Breakdown of nutrients into monomers.
• Gastric Juices
  • Hormone: Gastrin stimulates secretion.
  • Components:
    • Hydrochloric Acid: Breaks down proteins, kills pathogens.
    • Enzymes: Operate in acidic environment.
    • Mucus: Protects stomach lining, aids digestion.
• Chyme: Mixture of food bolus and gastric juices ready for absorption.

Terminology Recap

• Teeth: Incisors, canines, premolars, molars.
• Salivary glands: Parotid, sublingual, submandibular.
• Digestive Organs: Esophagus, stomach, pharynx, epiglottis.
• Processes: Peristalsis, digestion (mechanical and chemical), absorption, assimilation, egestion.
• Substances: Gastric juice (hydrochloric acid, enzymes, mucus), chyme.
• Cells: Goblet cells.