Digestive System

Presented by: Dr M. Arianmanesh PhD in Reproductive and Developmental Biology Dept. of Anatomical Sciences Today we will discuss:

• Histological layers of alimentary canal • Oral cavity • • • Teeth • Esophagus • Stomach • Small intestine • Large intestine • (GIT) tract: • Upper GIT: Oral cavity + Esophagus + Stomach • Lower GIT: Small intestine + colon + Rectum + anal canal

• Accessory digestive organs: • Liver • Pancreas • Gall bladder • Salivary glands Histological Layers of Alimentary Canal • Mucosa: • Epithelium • Lamina propria: • Loose CT • Contains lymphoid tissue and glands • Muscularis mucosa: • 1 or 2 layers circular smooth muscle

• Submucosa: Meissner’s/Submucosal Plexus • Dense CT or loose CT • Present in some parts • Contains lymphatic follicles in ileum & appendix • Contains mucus glands in esophagus & deodenum Continued… Histological Layers of Alimentary Canal • Muscularis externa: Myenteric/Auerbach’s Plexus • Two layers: • Inner circular layer: • Sphincters • Outer longitudinal layer

• Serosa: (Visceral peritoneum) • Mesothelium + loose underlying CT • From stomach to end • Adventitia: • CT • such as esophagus Meissner’s Plexus Auerbach’s Plexus Histological Layers of Digestive System

Mucosa Epithelium Submucosa Lamina Propria (LP) Muscularis Inner Circular Externa Outer Longitudinal Muscularis Mucosa

Serosa (or) Adventitia

Oral Cavity • Epithelium: • , oral surface of and soft : • Non keratinized stratified squamus • and gingiva: • Keratinized stratified squamus: • Orthokeratinized: • Squamus cells without nucleus • Parakeratinized: • Most squamus cells contain pycnotic nucleus

Orthokeratinized Ep. Parakeratinized Ep. Lip • Vermilion border • : Keratinized stratified squamous epithelium • Vermilion zone: • Very thin keratinized epithelium • Oral (Labial): • Non keratinized stratified squamous epithelium • Fibers of orbicularis oris muscle in submucosa

Vermilion Border

Vermilion Zone D A

C

B A: Skin B: Vermillion Zone C: Oral (Labial) Mucosa D: Minor Salivary Glands Tongue • Ventral of tongue: • Non keratinized stratified squamus EP. • Dorsal of tongue: • Median sulcus • Terminal sulcus: • Base of the tongue: Post. 1/3 • Lingual tonsil • Body of the tongue: Ant. 2/3 • Lingual papillae: • Filiform: • Keratinized Projections (2-3 mm) Continued… Tongue • Fungiform: • Non keratinized Ep. • Contains taste buds

C

A B A

A. Fungiform Papilla B. Filiform Papilla Continued… Tongue • Foliate: A few taste buds Continued… Tongue • Circumvallate: 8-12 • Surface epithelium: Keratinized • Wall epithelium: Nonkeratinized, presence of taste buds • Von Ebner’s Glands (Serous Glands)

Taste Buds • Unique sense organ • Barrel shaped bodies in EP of circumvallate, foliate & fungiform papillae • Found in , epiglottis, larynx & • Cells of : • 10-14 Cells • Taste pore • In LM? Continued… Taste Buds • In EM: • 4 Types of cells: • Type I: Supporting cells (60%) • Type II: Supporting cells (30%) • Type III: Gustatory cells (7%) • Type IV: Basal cells (3%) Lingual Glands • Lingual: • Anterior: Mixed • Middle: Serous (Von Ebner) • Posterior: Mucous (Weber) Teeth

Deciduous/Milk Teeth Permanent Teeth Structure of Tooth

• Crown: • Dental pulp • Dentin • Enamel • Neck • Root: • Dental pulp • Dentin • • Periodontal ligament (PDL) • Alveolar bone

Woven bone Dental Pulp

Pulp Horns

Pulp Chamber Located in Crown

Accessory Canals/Lateral Canal Root Canal Treatment Failures

Root Canal Located in Root

Apical Foramen Dental Pulp • Specialized loose connective tissue • Composition of the dental pulp • Extracellular matrix • Cells: • Fibroblast • Macrophage • Plasma cell • Undifferentiated mesenchyme cell • Odontoblasts surrounding pulp • Blood vessels and nerves Dentin • Composed of: • 70% Mineral Materials:

• Hydroxyapatite [Ca10 (PO4)6(OH)2] • 20% Organic Material: • 90% Collagen: Type I • 10% glycosaminoglycans and glycoproteins • 10% Water

• Yellow • Odontoblast cells: • Apical cytoplasmic process • Dentinal tubule • Predentin and dentin Odontoblast layer

Predentin

Dentinal tubules Enamel • Composed of: • 95-96% Mineral Materials: Hydroxyapatite • 4% Organic Material & Water: • Amelogenins (90%) • Non-amelogenins: (10%) • Enamelin • White • Ameloblasts: • Tall columnar • Tom’s process • Disappear after amelogenesis • Thinnest at the neck (cementoenamel junction) • Thickest at the cusps Structure of Enamel

• Rod enamel Keyhole shape • Interrod enamel • Rod sheath: Ameloblastin protein pcw = Proximal Cell Web dcw= Distal Cell Web Cementum • Composed of: • 45-50% Mineral Material (Hydroxyapatite) • 50-55% Organic Material: • 90% collagen type I • Acellular cementum: • Next to dentin • Cellular cementum: • Cementoblasts • Cementocytes Periodontal Ligament (PDL) • Dense specialized connective tissue • Location: between cementum & alveolar Bone • Fibers: • Collagen (type I) Vitamin C Deficiency • Oxytalan • Cells: • Fibroblasts • Cementoblasts • Osteoblasts and osteoclasts • Ground Substance Gingiva/Gum • Free (Marginal), Attached & Interdental Gingiva • Thick Orthokeratinized or Parakeratinized Stratified Squamous EP • Attached Gingiva Attached to the Neck of the Tooth by Junctional Ep •

Esophagus • Mucosa: 25-30 cm • Epithelium: • Nonkeratinized stratified squamus • At the end: Simple columnar • Mucus glands in LP • Submucosa: Muscularis mucosa • loose CT • Mucus glands • Muscularis externa: • 1/3 superior: Striated • 1/3 middle: Striated + Smooth • 1/3 inferior: Smooth (inner circular + outer longitudinal) Myenteric/Auerbach’s Plexus • Adventitia: Loose CT • In thorax • Serosa in abdominal esophagus

Longitudinal section of esophagus

Stomach

• Mucosa: • Epithelium: • Simple columnar • Gastric pit • Secretes bicarbonate-buffered mucus • LP contains glands • Submucosa: Muscularis mucosa • Fibroelastic CT • Rugae • Muscularis externa: • Innermost oblique • Intermediate circular: • Pyloric sphincter • Outermost longitudinal • Serosa Gastric Glands • Cardiac & pyloric glands: • Mucosal glands • Fundic & body glands: • Gastric glands • High in number of glands • Simple & compound tubular glands • Three parts in one gland: • Pit • Neck • Base Continued… Gastric Glands • Gastric glands: • Mucous neck cells: • Between parietal cells • Secretion of acidic mucous • Parietal cells/Oxyntic: • Big pyramidal • Acidophilic • In all parts of gland • High in mitochondria • Long microvilli • Secretory canaliculi • HCL secretion • Intrinsic factor: • Absorption of vitamin B12 • Anemia Continued… Gastric Glands • Chief/Zymogenic cells: • Pyramidal • At the base of the gland • Basophilic cytoplasm • Zymogen granules • Secretion of: • Pepsinogen Pepsin • Lipase • Renin • Endocrine cells/APUD/Argentaffin: • Between chief cells • Small & round • Secretion of: • APUD in fundus: Seretonin • APUD in pyloric: Gastrin • Stem cells/Regenerative cells: • At the neck of the gland • Small, basal nucleus

Layers of the Stomach Gastric Pits & Glands Gastric Glands Neck of the Glands Base of the Glands

Small Intestine • Duodenum (25 cm) • Jejunum (2.5 m) • Ileum (3.5 m) Small Intestine • Designed for absorption: • Great length: 5-7 m • Plicae circulares/Kerckring’s valves: • Penetration of submucosa toward mucosa • Increasing 3-fold of mucosa • Villi: • 1-1.5 mm in height • Penetration of LP toward EP • Contains: • Blood vessels • Lymphatic/lacteal vessels • Smooth muscle cells • Increasing 10-fold of mucosa • Microvilli: • Striated border • Increasing 20-fold of mucosa • Crypts/Lieberkuhn’s glands 600-fold

Continued… Small Intestine • Mucosa: • Epithelium: • Simple columnar/absorptive cells • Brush border • LP: • Peyer’s patches in ileum

Muscularis mucosa • Submucosa: • Relatively dense CT • Brunner’s glands in duodenum: • Mucus glands • Muscularis externa • Serosa

Continued… Cells of Mucosa • Absorptive cells: • In both villi & crypts • Brush border • Glycocalyx • Membranes of microvilli contains different enzymes: • Disaccharidase • Aminopeptidase • Enterokinase in duodenum: • Trypsinogen from pancreas to Trypsin • Goblet cells: • In both villi & crypts • Increased toward end of intestine • Paneth cells: • At the base of gland • Tall pyramidal • Acidophilic granules • Secretion of lysozyme & defensin Continued… Cells of Mucosa • Endocrine cells/APUD: • Base of the gland • Secretions: • Secretin • Cholecystokinin • Somatostatin • Substance P • Neurotensin • Undifferentiated cells • M/Microfold cells: • In Ep. Overlying lymphatic follicle • Without microvilli • Basolateral folds • Antigen presenting cells

Duodenum

• Leaf-like villi • Brunner’s glands: • Mucous secretion • pH: 8-9.5 Jejunum

• Long finger-like villi Ileum

• Peyer’s patches • M-cells in the EP. Covering Peyer’s patches Ileum Muscularis Externa

Myenteric Plexus

Fat Absorption

Large Intestine/Colon • 1.4-1.8 m • Parts: • Cecum • Appendix • Colon: • Ascending • Transverse • Descending • Sigmoid • Rectum Continued… Large Intestine/Colon

• Mucosa: • Absence of pelica & villi • Epithelium: • Simple columnar • Short & irregular microvilli • Low ability of absorption • Water absorption • Cells of epithelium: • Absorptive cells • Goblet cells • LP: High lymphatic follicles

Muscularis mucosa • Submucosa: • High lymphatic follicles Continued… Large Intestine/Colon • Muscularis externa: • Inner circular • Outer longitudinal: • 3 muscular bands called Teniae coli • In rectum: • Similar to small intestine • Serosa Continued… Large Intestine/Colon

• Cells of gland: • Absorptive • Goblet • Undifferentiated • APUD

Appendix • 5-10 cm • High lymphatic follicles in LP & submucosa

10-year-old child 36-year-old man Anal Canal • 2-3 cm • Mucosa: • Epithelium: • Simple columnar • Nonkeratinized stratified squamus • Keratinized stratified squamus • LP: • Large venus network • Hemorrhoid (enlarged veins) • Columns of morgagni/Anal columns • Anal sinuses • Pectinate line • Muscularis externa: • Inner circular: Involuntary sphincter • Outer striated: Voluntary sphincter

Epithelium of Anal Canal