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 Lip Tongue Teeth Esophagus Stomach Small intestine Large intestine
Gastrointestinal tract (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: Two layers: Inner circular layer: Sphincters Outer longitudinal layer Myenteric/Auerbach s Plexus 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 Submucosa Muscularis Externa Inner Circular Outer Longitudinal Epithelium Lamina Propria (LP) Muscularis Mucosa Serosa (or) Adventitia
Oral Cavity Epithelium: Cheeks, oral surface of lips and soft palate: Non keratinized stratified squamus Hard palate and gingiva: Keratinized stratified squamus: Orthokeratinized: Squamus cells without nucleus Parakeratinized: Most squamus cells contain pycnotic nucleus Orthokeratinized Ep. Parakeratinized Ep.
Vermilion border Lip Skin: 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
A D 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 Fungiform: Non keratinized Ep. Contains taste buds Tongue 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)
Unique sense organ Taste Buds Barrel shaped bodies in EP of circumvallate, foliate & fungiform papillae Found in soft palate, epiglottis, larynx & pharynx Cells of taste bud: 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: Anterior: Mixed Middle: Serous (Von Ebner) Posterior: Mucous (Weber) Lingual Glands
Teeth Deciduous/Milk Teeth Permanent Teeth
Crown: Dental pulp Dentin Enamel Neck Root: Dental pulp Dentin Cementum Periodontal ligament (PDL) Alveolar bone Woven bone Structure of Tooth
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
Composed of: Dentin 70% Mineral Materials: Hydroxyapatite [Ca 10 (PO 4 ) 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
Composed of: Enamel 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 Interrod enamel Keyhole shape 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) Oxytalan Cells: Fibroblasts Cementoblasts Osteoblasts and osteoclasts Ground Substance Vitamin C Deficiency
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 Gingival sulcus
Esophagus Mucosa: 25-30 cm Epithelium: Nonkeratinized stratified squamus At the end: Simple columnar Mucus glands in LP Submucosa: loose CT Mucus glands Muscularis mucosa Muscularis externa: 1/3 superior: Striated 1/3 middle: Striated + Smooth 1/3 inferior: Smooth (inner circular + outer longitudinal) Adventitia: Loose CT In thorax Serosa in abdominal esophagus Myenteric/Auerbach s Plexus
Longitudinal section of esophagus
Stomach Mucosa: Epithelium: Simple columnar Gastric pit Secretes bicarbonate-buffered mucus LP contains glands Muscularis mucosa Submucosa: 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
Neck of the Glands Gastric Glands Base of the Glands
Duodenum (25 cm) Jejunum (2.5 m) Ileum (3.5 m) Small Intestine
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 Endocrine cells/apud: Base of the gland Secretions: Secretin Cholecystokinin Somatostatin Substance P Neurotensin Cells of Mucosa Undifferentiated cells M/Microfold cells: In Ep. Overlying lymphatic follicle Without microvilli Basolateral folds Antigen presenting cells
Leaf-like villi Brunner s glands: Mucous secretion ph: 8-9.5 Duodenum
Long finger-like villi Jejunum
Peyer s patches M-cells in the EP. Covering Peyer s patches Ileum
Ileum
Muscularis Externa Myenteric Plexus
Fat Absorption
1.4-1.8 m Parts: Cecum Appendix Colon: Ascending Transverse Descending Sigmoid Rectum Large Intestine/Colon
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