Digestive System

• Digestive System

  Food undergoes six major processes: Ingestion, Propulsion, Mechanical digestion, Chemical digestion, Absorption, Defecation
• Ingestion


  Process of eating
• Propulsion

  1. Passing of food down the GI tract

  2. Swallowing: voluntary

  3. Peristalsis: reflex, involuntary, involves alternating contractions of muscles in body walls of GI organs
• Mechanical digestion


  1. Prepares food for chemical digestion

  2. Includes chewing, mixing with saliva by tongue action, churning in stomach
• Chemical digestion


  1. Catabolic steps in which food is broken down to basic building blocks

  2. Accomplished by enzymes in digestive juices
• Absorption


  Passage of food particles into the blood-lymph
• Defecation


  Elimination of indigestible food substances
• Main Parts of Human Digestive System

  • Mouth
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine
• Accessory Parts of Human Digestive System

  • Liver
  • Pancreas
  • Gallbladder
  • Salivary Gland
• Mouth


  Two major processes: Mastication (Chewing) and Secretion of Saliva
• Mastication (Chewing)


  • Breaks down large food molecules
  • Increases surface area of food particles
• Saliva


  • Contains salivary amylase (ptyalin) that digests starch to maltose
  • Lubricates and moistens food
• Salivary Glands

  • Parotid
  • Submaxillary
  • Sublingual
• Teeth


  • Bonelike structure in the mouth used for mastification or chewing
  • Parts: Crown, Neck, Root
• Types of Teeth


  • Incissors (8)
  • Canines (4)
  • Premolars (8)
  • Molars (12)
• Tongue


  Assists in mastification (chewing), deglutition (swallowing) and speech
• Pharynx


  Short tube-shaped cone that connects the mouth to the esophagus
• Esophagus

  • Mucus muscular membrane lined tube
  • Peristalsis: Involuntary process of muscular contraction forcing the bolus (food) down to the stomach
• Stomach


  • Hollow, muscular holding pouch for food
  • Contains rugae: muscular folding surface responsible for expansion and contraction
  • Parts: Fundus, Body, Pylorus
• In humans, the stomach has a relaxed volume of about 45 ml, it generally expands to hold about 1 litre of food, but can hold as much as 4 liters
• Small Intestine


  • Coiled tube about 7 meters long where most digestion and absorption of nutrients take place
  • Parts: Duodenum, Jejenum, Ileum
  • Absorption occurs through villi
• Large Intestine or Colon


  • Wider and 1.5 meters long
  • Responsible for absorption of water molecules or fluid substances
  • Parts: Ascending, Transverse, Descending
  • Rectum stores undigested food
  • Anus releases stool or feces through defecation
• Liver


  • Largest organ in the mammalian body
  • Secretes bile which is stored in the gallbladder
  • Bile breaks down fats into tiny droplets through emulsification
  • Roles: Regulates sugar/glucose, Breaks down excess RBC, Storage of blood, Detoxification, Generation of heat
• Pancreas


  • Endocrine gland that secretes insulin hormone to convert excess glucose into glycogen for storage
  • Exocrine gland that secretes pancreatic juice in the duodenum containing lipase, trypsin and pancreatic amylase for digestion of lipids, proteins and starch
• Salivary Gland Types

  • Sublingual
  • Parotid
  • Submandibular
• Gallbladder


  • Pear-shaped sac attached to the liver by the cystic duct
  • Stores bile, a yellowish-green fluid produced by liver cells
  • Bile salts act as emulsifying agents in the digestion and absorption of fats
  • Cholesterol and bile pigments are excreted from the body in the bile