Lecture 32: Upper GI Histology I Flashcards
Describe the general epithelium of the GI tract
Stratified squamous at either end and simple columnar epithelium most of length with glands
Describe the general musculature of the GI tract
Skeletal muscle at either end and smooth muscle for most of length
What causes intrinsic rhythmicity (including peristalsis) of GI tract?
Mostly due to enteric nervous system, but also receives input from sympathetic and parasympathetic nervous system
Name 3 peptide neurotransmitters
Bombesin, Motilin, vasoactive intestinal peptide
Describe protective mechanisms of GI tract
Production of large amounts of mucous, rapid turnover of epithelial cells in harsh environments such as the stomach and small intestine
Components of oral cavity mucosa
Stratified squamous epithelium, basement membrane, lamina propria; lip has core of skeletal muscle and internal poorly keratinized stratified squamous epithelium on lamina propria with high papillae
Cheek
Structure similar to lip, but with abundant elastic fibers in submucosa - continuous with fibers surrounding striated muscle and lamina propria = distensibility
What three embryonic tissues interact in development of teeth?
Ectoderm forms enamel organ, Neural crest and mesoderm give rise to dental papilla
List the three structures derived from the epithelial bud
- Enamel organ: forms enamel, caps dental papilla
- Dental papilla: condensation of mesenchyme that gives rise to dentin and pulp
- Dental sac/follicle: CT sac surrounding enamel organ and dental papilla and forms cementum and periodontal membrane
Odontoblasts
Form dentin matrix, single layer of cells lining pulp cavity; contain Tomes’ dentinal fibers and increment lines of Ebner and Owen
Tomes’ dentinal fibers
Cytoplasmic extensions of odontoblasts continuing through predentin and dentinal layers to dentin-enamel junction; occupy dentinal tubules
Ameloblasts
Form enamel which covers only tooth crown; each prism of enamel is formed by one ameloblast; secreting apical domains = Tomes’ processes; increment lines of Retzius = periods of rhythmic growth
Enamel
Hardest substance in body, 96% inorganic salts, 4% organic material and water; laid down in prisms
Pulp
Originates from dental papilla containing condensed mesenchyme
Cementum
Cells of dental sac differentiate into cementoblasts which deposit cementum on dentin of root from neck to apex; cementum has coarse collagen fibers (Sharpey’s) in a bone-like calcified matrix - holds teeth in place
Periodontal membrane
CT formed from dental sac; highly metabolically active; binds cementum to bony socket. Allows limited movement, absorbs pressure of mastication and prevents from damaging alveolar bone
What is the sulcus terminalis?
Boundary between the anterior 2/3 and posterior 1/3 of the tongue
Lingual papillae
Appear on oral portion as surface projections - formed of a central core of CT lamina propria covered by stratified squamous epithelium (4 types)
Filiform papillae
Most numerous, conical appearance, evenly distributed over entire oral upper portion; lack taste buds
Fungiform papillae
Relatively few in number, interspersed singly among parallel rows of filiform papillae; Taste buds present only on oral surface of epithelium in contradistinction to the position of the taste buds on the circumvallate papillae whose taste buds are primarily located in lateral walls
Foliate papillae
Rudimentary in humans; pharyngeal portion free of papillae but contains lingual tonsils
Circumvallate papillae
Located along sulcus terminalis as projections surrounded by a “moat”; taste buds present on lateral walls; Ducts of von Ebner’s glands open into moat
Sustentacular cells
Supportive spindle shaped cells arranged like barrel staves to surround inner taste pore at the base (part of taste bud derived from single stem cell)
Taste cell
Receptor; each cell is long and slender with elongated central nucleus and terminates as short taste hair which projects into external opening called outer taste pore; apical microvilli with taste receptors; basal part of cell releases neurotransmitters; distributed between supporting cell (derived from single stem cell)
Name the 4 layers of the gut tube
Mucosa, Submucosa, Muscularis Externa, Adventitia/Serosa
Mucosa of gut tube
Stratified squamous to simple columnar epithelium; secretory/absorptive/protective functions; lamina propria with loose areolar CT, 1-3 smooth muscle layers
Submucosa of gut tube
Vascularized, dense irregular CT, containing Meissner’s nerve plexus
Meissner’s plexus
Plexus of the enteric nervous system that regulates local secretions, blood flow, and absorption
Muscularis externa of gut tube
Inner circular layer of smooth muscle, outer longitudinal layer of smooth muscle; regulates size of lumen and rhythmic lumen of gut tube; contains Auerbach’s nerve plexus
Myenteric/Auerbach’s plexus
Plexus of the enteric nervous system that coordinates muscle activity of the gut wall
Serosa/Adventitia of gut tube
Dense irregular CT forming peritoneum and including adipose tissue
What immunoglobulin is the first line of defense found coating the mucosal epithelium?
IgA
M cells
Specialized squamous cells which transport food antigens to lymph follicles
Functions of esophagus
Digest food, add mucous to food bolus
Specialization in mucosa of esophagus
Stratified squamous non-keratinized epithelium, mucous glands in lamina propria and submucosa
Specialization in muscularis of esophagus
Transition from skeletal muscle in upper third to mixture of skeletal/smooth muscle in middle third and only smooth muscle in lower third
Esophageal-Stomach transition zone
Transition from stratified squamous epithelium in esophagus to simple columnar epithelium of stomach; frequent site of cancer
Gastric mucosa
Consists of simple columnar epithelium with goblet cells; protective insoluble mucous; rugae
Rugae of stomach
mucosal folds most prominent in empty stomach; NOT associated with increased surface area
Cardia of stomach
Lies opposite apex of heart, contains mostly mucous glands
Fundus of stomach
Contains gastric glands, mucous neck cells, parietal cells, chief cells, stem cells, enteroendocrine cells
Body of stomach
Contains gastric glands (long tubular glands extending down into muscularis mucosae)
Pylorus of stomach
Contains mucous glands and hormone-secreting enteroendocrine cells
