GI SYSTEM

• Gastrointestinal system


  Pathway 7-7.9 meters (23-26 feet) in length from mouth to the esophagus, stomach, small and large intestines, rectum to the terminal structure which is the anus
• Components of the gastrointestinal system

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
• Accessory organs of the gastrointestinal system

  • Teeth
  • Tongue
  • Salivary glands
  • Liver
  • Gallbladder
  • Pancreas
• Functions of the gastrointestinal system

  • Ingestion
  • Secretion
  • Digestion
  • Absorption
  • Defecation/Elimination
• Mouth (Oral or Buccal cavity)


  An oval-shaped cavity inside the skull, with two main functions: eating and speaking
• Parts of the mouth

  • Lips
  • Vestibule
  • Mouth cavity
  • Gums
  • Teeth
  • Hard and soft palate
  • Tongue
  • Salivary glands
• Digestive process in the mouth

  1. Chewing (mechanical digestion)

  2. Salivary amylase breakdown of starches (chemical digestion)

  3. Deglutition (swallowing)
• Lips


  • Muscular structures formed by orbicularis oris muscle
• Cheeks


  • Form the lateral wall of the oral cavity
• Lips and cheeks


  Important in the process of mastication or chewing, moving the food around and holding it in place for the teeth
• Tongue


  Muscular accessory organ that maneuvers food for chewing and occupies most of the oral cavity, plays a major role in swallowing, a major sensory organ for taste, and a major organ for speech
• Types of teeth


  • Incisors
  • Canines
  • Premolars
  • Molars
• Incisors


  Used to bite into food
• Canines


  Sharpest teeth, used for tearing apart food
• Premolars


  Used for tearing and crushing food, have a flat biting surface
• Molars


  Largest teeth, used for grinding, tearing, and crushing food, have a large flat biting surface
• Regions of a tooth

  • Crown
  • Neck
  • Root
• Pulp cavity


  Located at the center of the tooth, filled with blood vessels, nerves and connective tissue
• Dentin


  Surrounds the pulp cavity
• Enamel


  Extremely hard acellular substance that covers the dentin, protects the tooth against abrasions and acids
• Salivary glands


  • Parotid
  • Submandibular
  • Sublingual
• Parotid glands


  Serous glands located inferior & anterior to ears, produce saliva to moisten the mouth, help with chewing, swallowing, phonating, and digestion
• Submandibular glands


  Mixed serous and mucous salivary secretions, important for the lubrication of food during mastication to enable effective swallowing and aid digestion
• Sublingual glands


  Secrete saliva into the mouth from under the tongue, the smallest of the three major salivary glands, produce more mucous
• Saliva


  Contains 99.5% water, salivary amylase, mucus and other solutes, dissolves food and starts digestion of starches
• Pharynx/Throat


  Tube-like structure that connects the nasal and oral cavities to the larynx, a passageway for air and food
• Parts of the pharynx

  • Nasopharynx
  • Oropharynx
  • Laryngopharynx
• Nasopharynx


  Behind the nasal cavities, passageway for air only
• Oropharynx


  Located in the middle portion of the pharynx behind the mouth, passageway for both air and food
• Laryngopharynx


  Located in the lower portion of the pharynx, opens into the larynx and the esophagus, passageway for both air and food
• Esophagus


  Located in the mediastinum, anterior to the spine and posterior to the trachea and heart, about 25 cm long, serves as the passage of food bolus from mouth to stomach by peristalsis
• Upper esophageal sphincter (UES)


  Skeletal muscle that controls entry to the esophagus
• Lower esophageal sphincter (LES)

  Smooth muscle that regulates entry to the stomach
• Stomach


  A hollow muscular organ with a capacity of 1500 ml, located in the left upper quadrant of the abdomen, stores and mixes food with secretions, secretes digestive fluids, and propels partially digested food into the small intestine
• Regions of the stomach

  • Cardia
  • Fundus
  • Body
  • Pylorus
• Epithelial cells in the stomach

  • Surface mucous cells
  • Mucous neck cells
  • Parietal cells
  • Endocrine cells
  • Chief cells
• Surface mucous cells


  Located in the inner surface of the stomach, produce mucus that protects the stomach lining
• Parietal cells


  Produce hydrochloric acid and intrinsic factor
• Chief cells


  Produce pepsinogen, a precursor of the protein digesting enzyme pepsin
• Functions of the stomach

  • Mechanical digestion
  • Secretion