Chapter 13 Digestive tract

---Digestive system: Digestive tract Digestive gland

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

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

1) mucosa ---epithelium: stratified squamous epi.: protecting simple columnar epi,: digestion and absorption ---lamina propria: LCT-compact CT: contain more cells and fiber BV, LV-capillaries Lymphoid T glands: structures formed by invagination of epi. into lamina propria ---muscularis mucosa: a thin layer of SM

2) submucosa: more dense CT small artery and vein, LV glands (esophagus and duodenum) submucosa N plexus: -multipolar N -unmyelinated NF -function: regulate the contract of SM and secreting of gland *Plica: projection of mucosa and submucosa

3) muscularis externa smooth muscle skeletal muscle inner circular and outer longitudinal *Nerve plexus: regulate the movement of M 4) adventitia: CT serosa: CT + mesothelium fibrosa: LCT

3. Esophagus 1) mucosa: epithelium: stratified squamous epi. lamina propria: compact CT muscularis mucosa: longitudinal arranged SM 2) submucosa: LCT esophageal gland: mucous gland

3) muscularis: inner circular and outer longitudinal upper 1/3: skeletal muscle middle 1/3: mixed of skeletal M and smooth muscle lower 1/3: smooth muscle 4) adventitia: fibrosa

4. Stomach ---dilated part ---store food temporarily ---digest protein primarily ---absorb part of water and Ions

1) Mucosa: ---plica-longitudinal ---shallow ditch- gastric area(2-6mm) ---gastric pit- small depressions

① epithelium: simple columnar epi surface mucous cell: -tall columnar -N ovoid, basally-located -mucinogen granule -tight junction -high HCO 3 - undissolved mucus less endocrine cell

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

* Fundic gland -long, branch tube liked gland: /neck, body and basa -five types of cells can be seen

a. chief cell or zymogenic cell ---structure: LM: columnar Round, basally-located Nucleus cytoplasm: /basal-basophilic /apical-zymogen granules EM: RER, Golgi apparatus ---function: secret pepsinogen

b. 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

---function: i. 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(intracellular secretort canaliculi) -function of HCl: HCl ↓ pepsinogen→pepsin kill the bacterium

ii. secret intrinsic factor- glycoprotein + VB12→absorption of VB12

c. mucous neck cell less, neck part columnar flattened, basally-located N pale stain in HE stain d. stem cell: undifferentiated cell e. endocrine cell ECL cell: secreting histamine, promote secretion of parietal cell D cell: secreting somatostatin, inhibit the secretion of parietal cell

* cardiac gland and pyloric gland : mucous gland, contain G cell, which secretes gastrin, to promote the secreting of parietal cell * Mucous-HCO 3 barrier: mm thick mucous HCl PH: H + + HCO 3 - → H 2 CO 3 →H 2 O + CO 2 ↑ bicarbonatase

③ Muscularis mucosa: inner circular and outer longitudinal arranged SM 2) submucosa : CT with BV, LV, N and fat cell 3) muscularis : thicker inner oblique middle circular outer longitudinal 4) advantitia : serosa

5. Small intestine ---duodenum ---jejunum ---ileum

1) Mucosa ---circular plica ---intestinal villus ---small intestinal gland

① epithelium: ---absorptive cell: microvilli: striated-border um long, 80nm in D, enlarge the surface area to 30 times cell coat: um -enzymes: trypsinogen, amylase - glucose and protein enzymes-adipose SER

---goblet cell ---endocrine cell: I cell: secreting cholecystokinin- pancreozymin S cell: secreting secretin

② lamina propria: CT (LC, macrophage, plasma cell and eosinophil and mast cell) a. villus: is the projection of epithelium and lamina propria epithelium: absorptive cell, goblet cell and endocrine cell lamina propria: CT with central lacteal, fenestrated cap. and SM

b. small intestinal gland: is the invagination of epi.into propria absorptive cell goblet cell endocrine cell stem cell Peneth cell

Peneth cell : LM: -pyramidal, basally- located, in groups -apical: acidophilic G- contain defensin(cryptdin), Lysozyme EM: -protein-secreting cell feature Function: related to immune function

③ muscularis mucosa: SM inner circular and outer longitudinal 2) submucosa: CT Large BV and LV duodenal gland: mucous gland- secreting epidermal growth factor, promote the epithelial cell proliferation of small intestine

3) muscularis: SM, inner circular and outer longitudinal 4) adventitia: serosa and less fibrosa

6. Large intestine ---absorb water and ions ---structure feature: a. no villus and no circular plica b. well-developed large intestinal gland c. contain more goblet cells d. taeniae coli: longitudinal bunds bag coli