Bio 134

• Functions of the digestive system


  • Ingestion
  • Mechanical processing
  • Digestion
  • Secretion
  • Absorption
  • Elimination
• Components of the digestive system

  • Alimentary Canal
  • Accessory Digestive Organs

  
• Parts of the Alimentary Canal

  • Oral Cavity
  • Oropharynx
  • Esophagus
  • Stomach
  • Small intestine (duodenum, jejunum, ileum)
  • Large intestine (cecum and appendix, ascending, transverse, descending, sigmoid colon)
  • Rectum
  • Anal canal

  
• Accessory Digestive Organs


  • Teeth
  • Tongue
  • Salivary Glands
  • Liver
  • Gall Bladder
  • Pancreas

  
• Wall of each digestive organ

  • Mucosa
  • Submucosa
  • Muscularis externa
  • Serosa or adventitia

  
• Parts of the Mucosa

  • Epithelium
  • Lamina propria
  • Muscularis mucosae

  
• Submucosa


  • Connective Tissue Layer
  • Blood vessels
  • Lymphatic vessels
  • Submucosal (Meissner's) plexus
  • Glands and lymph nodules

  
• Muscularis externa


  • Inner circular
  • Myenteric (Auerbach's) plexus
  • Outer longitudinal

  
• Muscularis externa variations


  • Oral cavity (skeletal)
  • Hard palate and gingiva (no muscle)
  • Upper third of esophagus (skeletal)
  • Lower third of esophagus (skeletal→smooth)
  • Stomach (3 layers: outer longi, middle circ, inner oblique)
  • Colon's outer longitudinal gathered into 3 bands
  • Anal canal = smooth → skeletal (sphincters)

  
• Serosa (adventitia)


  • Adventitia (thick CT and adipose without mesothelium)
  • Serosa (thin layer of LCT that is covered by mesothelium)
• General functions of the digestive system

  • Digestion
  • Absorption
  • Elimination
• Digestion


  1. Role of teeth, lip, cheek, tongue muscles

  2. Role of salivary gland (ptyalin)

  3. Role of esophagus (peristalsis; mucus)

  4. Role of stomach (pepsin; gastric juice; HCl,chyme)

  5. Role of small instestine (enterokinase, secretin, CCK, enterogastrone)

  6. Role of pancreas (pancreatic juice)

  7. Role of liver (bile) and gall bladder
• Absorption


  • Small Intestine – nutrients
  • Large Intestine – water

  
• Structural modifications of small intestine

  • Plicae circularis (intestinal fold)
  • Villi
  • Microvilli

  
• Absorption of nutrients


  1. Amino acids and sugars (blood capillaries → liver)

  2. Fatty acids → chylomicrons → lacteals → blood capillaries
• Elimination


  1. Undigested fraction and waste products → COLON

  2. Mucus is added and water is extracted

  3. Intestinal contents concentrate and solidify, forming

  4. Further dehydration and storage in the RECTUM

  5. Finally expelled through the ANAL CANAL
• Oral cavity


  • Bounded anteriorly, posteriorly, laterally, superiorly, inferiorly
• Oral cavity wall structure

  • Mucosa
  • Submucosa
  • Muscle and bone

  
• Lips


  • Transition from NKSE to KSE in the epidermis
  • Vermillion border
  • Hair follicle and keratin
• Tongue


  • Mass of skeletal muscle covered by a mucosa
  • Muscle arranged in bundles, separated by CT and cross each other in 3 planes
  • Arrangement gives tongue flexibility
• Tongue mucosa


  • Ventral surface (thin NKSSE underlain by lp)
  • Dorsal surface (SSE- only partly keratinized)
  • Anterior 2/3 separated by a V-shaped groove from posterior third
  • Behind the groove, epithelium invaginates to form the crypts of the lingual tonsils

  
• Types of lingual papillae

  • Filiform
  • Fungiform
  • Foliate
  • Circumvallate
• Taste buds


  • Ovoid structures within the stratified epithelium
  • Composed of gustatory cells, supportive cells, immature cells, basal stem cells
  • Basal end rests on a basal lamina, entered by afferent sensory axons
  • Apical end has microvilli projecting toward a taste pore

  
• Taste modalities


  • Sodium ions (salty)
  • Hydrogen ions from acids (sour)
  • Sugars and related compounds (sweet)
  • Alkaloids and certain toxins (bitter)
  • Amino acids such as glutamate and aspartate (umami)
• Tooth classification by shape

  • Incisors
  • Canines (cuspids)
  • Premolars (bicuspids)
  • Molars (tricuspids)
• Permanent (adult) teeth


  • Human adult normally have 32 permanent teeth arranged in 2 arches (maxillary and mandibular)
  • Each arch has 2 bilaterally symmetrical quadrants with 8 teeth in each quadrant
  • Dental Formula : 2 incisors, 1 canine, 2 premolars, and 3 molars
• Deciduous (baby) teeth


  • 20 deciduous teeth because molars are absent
  • Dental formula for 5 teeth in each quadrant: 2 I 1C 2 P
• Parts of a tooth

  • Crown
  • Root
  • Neck
  • Pulp cavity
• Dentin


  • Thick layer of bonelike calcified tissue
  • Composition: 70% hydroxyapatite crystals, organic components: type I collagen and GAGs
  • Tissue organization: odontoblasts, Tomes' fiber
• Enamel


  • Thick layer of calcified material covering the dentin of the crown
  • Composition: 95% hydroxyapatite, unique proteins: amelogenins & enamelins, no collagen
  • Organized as tightly-packed columns of hydroxyapatite called enamel rods (prisms)
• Odontoblasts


  Secrete predentin
• Predentin deposition


  Cells retreat, leaving Tomes' fiber
• Mineralization


  1. Cells release hydroxyapatite crystals into predentin

  2. Crystals serve as nucleation sites for further mineralization
• Dentin


  Odontoblast (O); pulp cavity (PC); predentin (P); dentin (D); odontoblast process (OP)
• Enamel


  Thick layer of calcified material covering the dentin of the crown
• Enamel is not considered a tissue when mature
• Composition of enamel


  • Mainly hydroxyapatite (95%)
  • Unique proteins: amelogenins & enamelins
  • No collagen
• Organization of enamel


  • Arranged as tightly-packed columns of hydroxyapatite called enamel rods (prisms)
  • Prisms are bound together by interrod enamel
• Enamel production


  1. Ameloblasts also recede as organic material being secreted

  2. Tomes' fibers of ameloblasts recede along with the cell, leaving behind a solid rod of organic preenamel

  3. Calcification begins at the periphery of each rod and proceeds toward its core
• Cementum


  • Bonelike tissue covering the dentin of the roots
  • Contains cementocytes that, like osteocytes, lie in lacunae, and produce the surrounding matrix
  • Helps to keep the roots in contact with the walls of the bone alveoli