Digestive tract

---Digestive system: Digestive tract Digestive gland This system is responsible for the mechanical and chemical breakdown of food material, and for absorbing these digestive products into the blood for use as nutrients by the individual cells and tissues of the body

Components of digestive tract ---oral cavity ---pharynx ---esophagus ---stomach ---small intestine ---large intestine

General plan of digestive tract ---Except for oral cavity and pharynx, all other organs share a similar histological plan

General Plan Mucosa(内膜） Submucosa（内膜下层） Epithelium Lamina propria (may contain glands) Muscularis mucosae (Smooth muscle) Submucosa（内膜下层） Loose C.T. may contain glands Meissner’s autonomic nerve plexus

Muscularis externa（肌层） Inner circular Myenteric (Auerbach’s) autonomic nerve plexus Outer longitudinal Tunica adventitia（外膜） Fibrosa or serosa (covered by mesothelium)

Esophagus Passage way for food from the pharynx to the stomach mucosa: epithelium: stratified squamous epithelium lamina propria: compact CT muscularis mucosa: longitudinal arranged smooth muscle submucosa: LCT esophageal gland: mucous gland

Muscularis externa: inner circular and outer longitudinal upper 1/3: skeletal muscle middle 1/3: mixed of skeletal muscle and smooth muscle lower 1/3: smooth muscle Tunica adventitia: a fibrous coat of loose connective tissue

Stomach ---dilated part ---store food temporarily ---digest food partially to form a semi-fluid mass, termed chyme ---absorb part of water and ions

Stomach (regions) Cardia (Cardiac junction) Surrounds esophageal entrance Fundic stomach defined histologically includes Fundus Body Pylorus (Pyloric junction) Pylorus is continuous with the duodenum

Stomach Histology Overview Mucosa Epithelium (simple columnar mucus-secreting) Lamina propria (gastric glands of different types) Muscularis mucosae (Smooth muscle) Submucosa Loose C.T. no glands Muscularis externa inner oblique, middle circular, outer longitudinal Tunica adventitia Mostly serosa

mucosa Rugae Longitudinal folds of mucosa A mucosal fold contains submucosa Gastric pits: small depressions, 3-5 gastric gland open into the bottom Diffuse lymphoid tissue and nodules may be present mucosa

Rugae in the stomach Mucosa Muscularis mucosa Submucosa Muscularis externa Rugae

Simple columnar epithelium Gastric pit Laminia propria between pits Cross section of gastric pits Simple columnar epithelium Gastric pit Laminia propria between pits

①epithelium: simple columnar epithelium surface mucous cell: -tall columnar -ovoid, basally-located nuclei -apical mucin granule -tight junction The mucus is secreted on to the epithelial surface to form a barrier layer which protects it from injury by ingested substance and the stomach’s own secretion of acid and enzymes.

②lamina propria: CT contains fibroblast, LC, plasma cell, mast cell and eosinophil, smooth muscle gastric gland (fundic gland)-oxyntic gland cardiac gland: mucous gland pyloric gland: mucous gland

* Fundic gland -long, branched or unbranched gland

Five type cells are found: Chief cells（主细胞） Parietal cells（壁细胞） Three part of gland: The neck The body The base Five type cells are found: Chief cells（主细胞） Parietal cells（壁细胞） Mucous neck cells Stem cells Enterendocrine cells neck body

chief cell or zymogenic cell ---structure: LM: columnar Round, basally-located Nucleus cytoplasm: /basal-basophilic /apical-zymogen granules EM: RER, Golgi complex ---function: secret pepsinogen (the precursor of pepsin)

parietal cell or oxyntic cell ---structure: LM: large, pyramidal or spherical round centrally-located nucleus eosinophilic cytoplasm EM: intracellular secretory canaliculus-invaginations tubulovesicular system mitochondria

1. secret hydrochloric acid (HCl) ---function: 1. secret hydrochloric acid (HCl) synthesis processes of HCl: in intracellular secretory canaliculus H+ K+ -ATP pump: get H+ from cell Cl- channel: get Cl- from blood H+ +Cl-→HCl function of HCl: pepsinogen→pepsin kill the bacteria

mucous neck cell stem cell enterendocrine cell less, neck part pale stain in HE stain secrete mucus stem cell undifferentiated cell enterendocrine cell ECL cell: secreting histamine, promote secretion of parietal cell D cell: secreting somatostatin, inhibit the secretion of parietal cell

Cardiac Junction Epithelial transition Stratified Squamous nonkeratinized to simple columnar

Small intestine Duodenum – first region, only about 25cm long, Jejunum – second region is roughly 2.5m long Ileum – last region is roughly 3.5m long Primary functions Transport food from stomach to Large intestine Secretion of digestive enzymes to facilitate digestion of food substances Absorption of food substances into blood and lymph vessels Secretion of certain hormones

Small Intestine Overview Mucosa Epithelium (simple columnar mucus-secreting) Lamina propria (intestinal glands) Muscularis mucosae (Smooth muscle) Submucosa loose C.T. (contain duodenal glands in the duodenum) Muscularis externa inner circular, outer longitudinal Tunica adventitia serosa (except for the duodenum)

Special structure of mucosa Plicae circulares Mucosa and submucosa are arranged in permanent, circular mucosal folds Intestinal villi Mucosal projections covered by epithelium and containing only lamina propria Crypt or intestinal glands Surrounded by lamina propria Extend to the muscularis mucosae

Plicae circulares Villi

Plicae circulares villi

Epithelium (Simple columnar) Absorptive cells Numerous, regular microvilli form striated-border Well formed junctional complex Plicae circulares, villi and microvilli are serve to increase the surface area of the small intestine by as much as 600-fold surface coat: a layer of glycoprotein filament, protect the underlying cells from mucolytic and proteolytic agent Goblet cells :secrete mucus to lubricate and protect the epithelium Enteroendocrine cells: produce hormones

striated-border

microvilli

lamina propria: LCT, macrophage, plasma cell and eosinophil and mast cell central lacteal: lymphatic vessel, absorb fat

Crypt or small intestinal gland: the invagination of epithelium into lamina propria absorptive cell goblet cell endocrine cell stem cell Peneth cell

Peneth cell: LM: -pyramidal in shape, locate in basal portion of the glands, in groups -apical: acidophilic granules- contain defensin (cryptdin), Lysozyme EM: -protein-secreting cell feature Function: related to immune function, anti-bacterial activity

Large intestine ---Consists of: -cecum -ascending colon -transverse colon -descending colon -sigmoid colon -rectum -anal canal --- function: absorb water and ions

Mucosa No villi or plicae circulares Glands are longer than in small intestine Single columnar epithelium contain numerous goblet cells but absorptive cells are still present Occasional solitary lymph nodules At anal junction there is an abrupt transition to stratified squamous non-keratinized epithelium.

Submucosa Muscularis externa Adventitia Similar to small intestine except nerve plexus are more easily found here Muscularis externa Inner circular layer is evident Outer longitudinal layer forms three bands, the taenia coli Adventitia Both serosa and fibrosa are found

Appendix (study by yourself) Mucosa is like the colon except Numerous lymph nodules are present in the young These decrease with age They break up the muscularis mucosae so that it is difficult to find The glands are also often not very evident. Submucosa and muscularis externa are like the rest of the colon

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