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What are the three components of the digestive system?
- Oral Cavity
- Alimentary Canal
- Digestive Glands
What are the functions of the oral cavity?
- Bolus formation
Describe the structure of the lips.
- Anterior margin of the oral cavity
- External aspect is the skin
- Intermediate (Vermillion) transition zone
- Internal aspect- 'wet' mucosa- continuous with the internal aspect of the cheeks
Describe the layers of the internal aspect of the lips.
- Epl: stratified squamous, non-keratinized
- L. Propria: dense, irregular CT
- Submucosa: Mucous glands
- Adventitia: Skeletal muscle- continuous with gingiva
- Transition/Vermillion zone- highly vascularized lamina propria
Describe the external aspect of the lips (skin).
- Epl: stratified squamous, keratinized epithelium
- Contains hair follicules and hair shafts
What is the function of the gingiva?
- Surround and encase roots of teeth
- Help protect the periodontal ligament via Junctional Epithelial collar- bacterial barrier which prevents periodontal disease
Describe the layers of the gingiva.
- Epl: lightly keratinized stratified squamous epl
- L. Propria and Submucosa: dense irregular CT, prominent collagen I fibers which mingle with the periodontal ligament
- Adventitia: Bone
What are the three sections of the tooth?
Enamel, dentin, and pulp chamber
What is the clinical crown?
All of the tooth above the gum line
What is the anatomical crown?
Everywhere on the tooth where there is enamel on top of the tooth
Describe the enamel of the tooth.
- Produced by ameloblasts on outer surface of developing tooth
- Enamel is non-vital/non-regenerative
- 96% Hydroxyapatite/mineralized
- Bacterial degradation=caries/cavities
Describe the dentin of the tooth.
- Produced by odontoblasts on inner surface of tooth lining pulp chamber
- Dentin is vital/regenerative
- 70% hydroxyapatite/mineralized
- Innervated/Pain if injured
Describe the pulp chamber of the tooth.
- Loose CT; high GAG content, jelly-like
- Highly vascularized and innervated
- Vessels and nerves enter and exit the pulp chamber via narrow root canal
What is cementum?
- Bone-like tissue, but avascular
- Produced by cementoblasts
- Some remodelling by odontoblasts
Describe the periodontal ligament.
- Coll I fibers embed in alveolus/spongy bone and cementum
- Highly regenerative
- Highly vascularized
- Highly innervated- pain and proprioception
What is the alveolus of the tooth?
Socket of spongy bone in mandible/maxilla
What is the palate?
- roof of the oral cavity
- Consists of a hard palate and soft palate
Describe the hard palate.
- Epl: Stratified squamous keratinized
- Adventitia: bone
Describe the soft palate:
- Epl: Stratified, squamous, nonkeratinized
- Adventitia: skeletal muscle
- Elevates with uvula during swallowing to close nasal cavity entrance to pharynx
Describe the structure of the tongue
- Mucosal specializations = papillae with taste buds
- Prominent posterior MALT= lingual tonsils
- Submucosal serous glands trap tastant molecules
- Adventitial intrinsic skeletal muscle manipulates chewed food into a bolus
What are the papillae of the tongue made up of?
Stratified squamous keratinized epithelium with a dense, irregular CT core
Describe the structure of taste buds.
- Spindle-shaped sensory receptor cells (I&II)
- Have apical microvilli in taste pore on apical surface of epithelium
- Tastant chemicals dissolved in serous fluid enter pore and bind to/activate G-coupled cell surface receptors on microvilli- downstream signals stimulate synapse-like release and activation of afferent sensory neurons
- Tastants can be sweet, sour, salty, or bitter
Name the components of the alimentary canal
Pharynx, esophagus, stomach, sm. intestine, lg. intestine, appendix, rectum, anal canal
What are the general components of the alimentary canal?
- Mucosa- endoderm-derived epl, Lamina propria was loose CT with MALT
- Muscularis mucosae- smooth muscle
- Submucosa- dense irregular CT, Meissner's Nerve Plexus
- Muscularis externa- inner circular/outer longitudinal muscle, Auerback's/Myenteric Nerve Plexus
- Adventitia- thin layer of CT, serosa=simple squamous epl covering, may or may not hand in mesentary which attaches to abdominal wall and contains blood vessels and nerves to/from alimentary canal
What is the function of the esophagus?
Muscular tube which conducts food from the pharynx to the stomach
Describe the layers of the esophagus.
- Mucosa: Epl is stratified squamous non-keratinized; lamina propria is loose CT.
- The mucosa is folded when emptied, leaves room for expansion by bolus of masticated food.
- Muscularis mucosa: smooth muscle
- Submucosa: Dense, irregular CT- contains submucosal glands
- Submucosal glands are seromucosal and have ducts which carry the secretions to the surface.
- Muscularis externa: Upper portion is skeletal muscle while the lower portion is smooth muscle (gradual blend)
What is the gastro-esophageal junction?
A transition from stratified squamous epithelium to columnar epithelium, plus there is a slight thickening of the M. externa; becomes the lower esophageal sphincter.
What is Barrett's syndrome?
- Pre-malignant metaplasia of lower esophageal epithelium
- Acid comes up from the stomach and irritates the esophagus. The esophageal epithelium wants to produce mucosa to protect itself, so it switches to simple columnar epithelium.