digestive

• Swallowing (deglutition)

  1. Voluntary phase

  2. Pharyngeal phase

  3. Esophageal phase
• Voluntary phase of swallowing

  Food is being prepared to be swallowed but still in the oral cavity, can still decide to continue swallowing or spit it out
• Pharyngeal phase of swallowing

  Soft palate elevates, successive contractions of pharyngeal constrictor muscles, triggered by reflex from presence of food in throat, no longer under voluntary control
• Pharynx is a passageway for both the digestive and respiratory systems
• Esophagus

  Tube that connects the pharynx to the stomach, transports food to the stomach
• Cardia opening

  Where the esophagus joins the stomach, has a sphincter muscle called the cardiac sphincter
• Hyperacidity

  Can cause gastric juices to regurgitate into the lower esophagus, causing irritation and a burning sensation (heartburn)
• GERD (Gastroesophageal Reflux Disease)

  Chronic condition where gastric juices frequently regurgitate into the lower esophagus
• Treatment for GERD is symptomatic relief, usually by controlling hyperacidity
• Saliva contains the enzymes amylase and lysozyme
• Amylase

  Digestive enzyme that begins the chemical digestion of carbohydrates in the oral cavity
• Lysozyme

  Enzyme active against bacteria, not essential for digestion
• Mucus in saliva

  Important for lubrication before swallowing, prevents choking
• Salivary glands


  • Parotid
  • Submandibular
  • Sublingual
• There are 3 pairs of salivary glands, 6 in total, in the oral cavity
• Parotid glands secrete mainly serous (watery) saliva, submandibular glands secrete both serous and mucous saliva, sublingual glands secrete mainly mucous saliva
• Eruption of wisdom teeth (third molars) is a good indicator of maturity, as they usually erupt around 19-21 years old
• Teeth in a normal adult

  • Incisors
  • Canines
  • Premolars
  • Molars (including wisdom teeth)
• A normal adult has 32 permanent teeth, while children have 20 primary (deciduous) teeth
• Cleft palate is a congenital defect that causes difficulty in articulation and communication
• The palate (hard and soft) separates the oral and nasal cavities
• Swallowing

  1. Voluntary phase

  2. Pharyngeal phase

  3. Esophageal phase
• Voluntary phase of swallowing

  You can still decide to continue swallowing or spit out the food
• Pharyngeal phase of swallowing

  Bolus touches the back of the throat, soft palate elevates, successive contractions of pharyngeal constrictor muscles
• Esophageal phase of swallowing

  Food passes into the esophagus, peristaltic contractions of the esophagus to propel food to the stomach
• Stomach

  Expanded portion of the gastrointestinal tract that serves as a storage tank for food
• Stomach contents

  Semi-liquid consistency called chyme, mixed with gastric juices
• Stomach capacity

  Can hold up to 2 liters of food
• Stomach functions


  • Produce mucus
  • Produce hydrochloric acid
  • Produce enzymes for protein digestion
• Stomach mucosa


  Thick mucous layer that lubricates and protects the epithelial cells from the acidic pH
• Stomach epithelial cells


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

  Produce stomach mucus
• Parietal cells


  Secrete hydrochloric acid and intrinsic factor
• Endocrine cells


  Produce hormones and paracrine molecules to regulate digestion
• Chief cells


  Produce pepsinogen, the precursor to the protein-digesting enzyme pepsin
• Hydrochloric acid


  Converts pepsinogen into active pepsin, kills harmful microorganisms, provides acidic environment for digestion
• Pepsin


  Digests proteins by breaking down peptide bonds
• Intrinsic factor


  Allows for absorption of vitamin B12, prevents pernicious anemia
• Regulation of gastric secretions


  1. Cephalic phase

  2. Gastric phase

  3. Intestinal phase
• Smell, taste or thought of food

  Stimulates cephalic phase of gastric secretion