GI anatomy 1

• Humans are not hollow, but the GI system is a continuous tube from mouth to anus (7-9m) that is even longer in cadavers
• The lumen ('inside') of the GI tract is technically exposed to the outside environment
• Sections of the GI tube (organs) play roles in the digestion of food and handling of nutrients

  
• Gastrointestinal Organs


  • GI Tract: Oral cavity, Pharynx, Esophagus, Stomach, Small intestine (Duodenum, Jejunum, Ileum), Large intestine
  • Accessory Digestive Organs: Liver, Gall bladder, Pancreas
• Oral cavity


  Includes mouth, teeth, gums, tongue, palate, palatine tonsils. Food is ingested and prepared for digestion
• Lips


  • Upper and lower mobile muscular folds surrounding the mouth, covered externally by skin and internally by mucous membrane
  • Buccinator and orbicularis oris help keep food between upper and lower teeth, assist with speech
  • Labial frenula are free-edged mucosal folds in midline of lips that anchor lips to gingivae (gums)

  
• Cheeks


  • Form lateral walls of mouth, form over zygomatic bones and prominences, essentially same structure as lips (skin externally, mucous membrane internally)
  • Buccal fat pad more prominent with babies to reinforce cheeks and prevent collapse while sucking
• Cheek Dimples


  • Fovea buccalis, caused by contraction of zygomaticus major during smiling pulling skin inwards, genetic variation leads to more prominent dimples
• Gingivae (gums)


  • Fibrous tissue covered with mucous membrane, excellent blood supply and innervation
  • Alveolar processes (mandibular, maxillary) anchor points for gingivae, maintain integrity of dental arches, contain tooth sockets
  • Gingivitis can spread to other structures (teeth, connective tissue, etc.)
• Teeth


  • Hard conical structures set within alveolar processes, secured by periodontal ligaments, used in mastication (mechanical digestion) assisted by masseter and temporalis muscles, also assist in articulation
  • Children have 20 primary (deciduous) teeth, adults have 32 secondary (permanent) teeth of different types (incisors, canines, premolars, molars)

  
• Tooth Structure


  • Crown - visible, Neck - within gingivae, Root - anchored in alveolar process
  • Composed of dentin covered by enamel over crown and cementum over root
  • Pulp cavity contains vessels & nerves (CN V) that enter via root canal

  
• Tongue


  • Strong and mobile skeletal muscle that can assume a variety of shapes, involved in mastication, taste, deglutition (swallowing), articulation, and oral cleansing
  • Motor innervation by CN XII
  • Root of tongue is posterior 1/3 and relatively fixed, body of tongue is remaining portion which is visible and most mobile
  • Dorsum (top) and lateral surfaces have lingual papillae (taste buds: follate, vallate, fungiform, filiform)

  
• Taste Buds


  • Receptors for the five primary tastes: sweet, sour, salty, bitter, and umami (savory)
  • Taste receptors are found all over the tongue, not localized in a "taste map"
  • Genetic variation affects taste perception (e.g. PTC, sodium benzoate)
• Salivary Glands


  • Three glands: Parotid, Submandibular, Sublingual
  • Produce and deliver saliva to moisten mucous membrane, lubricate food, begin digestion of starches, and prevent tooth decay
• Pharynx


  • Nasopharynx - respiratory function only
  • Oropharynx - digestive + respiratory functions
  • Laryngopharynx - digestive + respiratory functions
• Abdominal Viscera


  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Spleen
  • Pancreas
  • Liver
  • Gallbladder
  • Kidneys
  • Adrenal glands
• Esophagus


  • Connects pharynx to stomach, has upper and lower esophageal sphincters, first third is skeletal muscle, second third is mixed, third third is smooth muscle, passes through esophageal hiatus of diaphragm
• Stomach


  • Expandable portion of digestive tract that can hold 2-3L, acts as a food mixer and reservoir, acidic gastric juice gradually converts food mass into liquid (chyme) to pass into small intestine

  
• Protein digestion begins in the stomach
• Stomach Layers


  • Mucosa - produce stomach acid, contain gastric folds (rugae)
  • Submucosa - thin layer with blood vessels, nerves, etc.
  • Muscularis externa - 3 layers of smooth muscle (oblique, circular, longitudinal) for stomach movement
  • Serosa (adventitia) - outermost layer for protection and support
• Parts of Stomach


  • Greater curvature - convex inferior border
  • Lesser curvature - concave superior border
  • Cardia - immediately distal to lower esophageal sphincter
  • Fundus - superior portion situated inferior to left dome of diaphragm
  • Body - between fundus and pyloric region
  • Pyloric region - includes pyloric antrum & pyloric canal, pylorus thickens to form pyloric sphincter
• Why do Canadians like the upper part of the stomach the best?
• Small Intestine


  • Three parts: Duodenum, Jejunum, Ileum
  • Duodenum - receives chyme from stomach, bile from common bile duct, bicarbonate from pancreas, and digestive enzymes from pancreas
• Gallbladder


  Small pouch inferior to liver that stores and concentrates bile produced in the liver, can be removed with minimal changes to digestive tract
• Bile


  Created in the liver, released to duodenum via common bile duct for emulsification of fats, excess is stored in gallbladder
• Pancreas


  • Divided into head, body, and tail, lies retroperitoneally posterior to stomach
  • Produces pancreatic juice (bicarbonate-based fluid to reduce acidity) and digestive enzymes for carbohydrates, fats, and proteins
  • Also produces glucagon to convert glycogen to glucose and insulin to facilitate glucose transport to muscle cells