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

Mucosa(EpitheliumLamina propria (may contain glands)Muscularis mucosae (Smooth muscle)SubmucosaLoose C.T. may contain glandsMeissners autonomic nerve plexusGeneral Plan

Muscularis externaInner circularMyenteric (Auerbachs) autonomic nerve plexusOuter longitudinalTunica adventitiaFibrosa or serosa (covered by mesothelium)

Esophagus Passage way for food from the pharynx to the stomachmucosa: epithelium: stratified squamous epitheliumlamina propria: compact CTmuscularis mucosa: longitudinal arranged smooth musclesubmucosa: LCT esophageal gland: mucous gland

Muscularis externa: inner circular and outer longitudinalupper 1/3: skeletal musclemiddle 1/3: mixed of skeletal muscle and smooth musclelower 1/3: smooth muscleTunica 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 entranceFundic stomach defined histologically includesFundusBodyPylorus (Pyloric junction)Pylorus is continuous with the duodenum

MucosaEpithelium (simple columnar mucus-secreting)Lamina propria (gastric glands of different types)Muscularis mucosae (Smooth muscle)SubmucosaLoose C.T. no glandsMuscularis externa inner oblique, middle circular, outer longitudinalTunica adventitiaMostly serosaStomach Histology Overview

mucosaRugaeLongitudinal folds of mucosaA mucosal fold contains submucosaGastric pits: small depressions, 3-5 gastric gland open into the bottomDiffuse lymphoid tissue and nodules may be presentmucosa

Rugae in the stomach Mucosa

Muscularis mucosa

Submucosa

Muscularis externaRugae

Cross section of gastric pitsSimple columnar epitheliumGastric pit

Laminia propria between pits

epithelium: simple columnar epitheliumsurface 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 stomachs own secretion of acid and enzymes.

lamina propria: CT contains fibroblast, LC, plasma cell, mast cell and eosinophil, smooth musclegastric gland (fundic gland)-oxyntic glandcardiac gland: mucous glandpyloric gland: mucous gland

* Fundic gland -long, branched or unbranched gland

Three part of gland:The neckThe bodyThe baseFive type cells are found:Chief cellsParietal cellsMucous neck cellsStem cellsEnterendocrine cellsneckbody

chief cell or zymogenic cell---structure: LM: columnar Round, basally-located Nucleuscytoplasm: /basal-basophilic /apical-zymogen granulesEM: 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 cytoplasmEM: intracellular secretory canaliculus-invaginations tubulovesicular system mitochondria

---function: 1. secret hydrochloric acid (HCl) synthesis processes of HCl: in intracellular secretory canaliculusH+ K+ -ATP pump: get H+ from cellCl- channel: get Cl- from bloodH+ +Cl-HCl

function of HCl:pepsinogenpepsinkill the bacteria

mucous neck cellless, neck partpale stain in HE stainsecrete mucusstem cell undifferentiated cellenterendocrine cell ECL cell: secreting histamine, promote secretion of parietal cell D cell: secreting somatostatin, inhibit the secretion of parietal cell

Epithelial transitionStratified Squamous nonkeratinized to simple columnar

Cardiac Junction

Small intestine Duodenum first region, only about 25cm long, Jejunum second region is roughly 2.5m longIleum last region is roughly 3.5m long

Primary functionsTransport food from stomach to Large intestineSecretion of digestive enzymes to facilitate digestion of food substancesAbsorption of food substances into blood and lymph vesselsSecretion of certain hormones

Small Intestine Overview

MucosaEpithelium (simple columnar mucus-secreting)Lamina propria (intestinal glands)Muscularis mucosae (Smooth muscle)Submucosaloose C.T. (contain duodenal glands in the duodenum)Muscularis externa inner circular, outer longitudinalTunica adventitiaserosa (except for the duodenum)

Special structure of mucosa

Plicae circulares Mucosa and submucosa are arranged in permanent, circular mucosal foldsIntestinal villiMucosal projections covered by epithelium and containing only lamina propriaCrypt or intestinal glandsSurrounded by lamina propriaExtend to the muscularis mucosae

Plicae circularesVilli

Plicae circularesvilli

Epithelium (Simple columnar)Absorptive cellsNumerous, regular microvilli form striated-borderWell 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 epitheliumEnteroendocrine cells: produce hormones

striated-border

microvilli

lamina propria: LCT, macrophage, plasma cell and eosinophil and mast cellcentral 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), LysozymeEM: -protein-secreting cell featureFunction: 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

MucosaNo villi or plicae circularesGlands are longer than in small intestineSingle columnar epithelium contain numerous goblet cells but absorptive cells are still presentOccasional solitary lymph nodulesAt anal junction there is an abrupt transition to stratified squamous non-keratinized epithelium.

SubmucosaSimilar to small intestine except nerve plexus are more easily found hereMuscularis externaInner circular layer is evidentOuter longitudinal layer forms three bands, the taenia coliAdventitia Both serosa and fibrosa are found

Mucosa is like the colon exceptNumerous lymph nodules are present in the youngThese decrease with ageThey break up the muscularis mucosae so that it is difficult to findThe glands are also often not very evident.Submucosa and muscularis externa are like the rest of the colonAppendix (study by yourself)

Appendix