Digestive tractDigestive tract

---Digestive system: ---Digestive system: • Digestive tract Digestive tract • Digestive glandDigestive gland

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

Components of digestive tractComponents of digestive tract

---oral cavity ---oral cavity

---pharynx---pharynx

---esophagus---esophagus

---stomach---stomach

---small intestine---small intestine

---large intestine---large intestine

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

a similar histological plana similar histological plan

• Mucosa(Mucosa(内膜）内膜）– EpitheliumEpithelium

– Lamina propria (may contLamina propria (may contain glands)ain glands)

– Muscularis mucosae (SmoMuscularis mucosae (Smooth muscle)oth muscle)

• SubmucosaSubmucosa （内膜下（内膜下层）层）– Loose C.T. may contain glLoose C.T. may contain gl

andsands

– Meissner’s autonomic nerMeissner’s autonomic nerve plexusve plexus

General PlanGeneral Plan

• Muscularis externaMuscularis externa（肌（肌层）层）– Inner circularInner circular

– Myenteric (Auerbach’s) autMyenteric (Auerbach’s) autonomic nerve plexusonomic nerve plexus

– Outer longitudinalOuter longitudinal

• Tunica adventitiaTunica adventitia（外（外膜）膜）– Fibrosa or serosa (covered Fibrosa or serosa (covered

by mesothelium)by mesothelium)

EsophagusEsophagus Passage way for food from the pharynx to the stoPassage way for food from the pharynx to the sto

machmachmucosa:mucosa:

• epithelium: stratified squamous epitheliumepithelium: stratified squamous epithelium• lamina propria: compact CTlamina propria: compact CT• muscularis mucosa: longitudinal muscularis mucosa: longitudinal arranged smooth musclearranged smooth muscle

submucosa:submucosa:

• LCTLCT• esophageal gland: mucous glandesophageal gland: mucous gland

Muscularis externa:Muscularis externa: • inner circular and outer longitudinalinner circular and outer longitudinal• upper 1/3: skeletal muscleupper 1/3: skeletal muscle• middle 1/3: mixed of skeletal muscle and smooth musmiddle 1/3: mixed of skeletal muscle and smooth mus

clecle• lower 1/3: smooth musclelower 1/3: smooth muscleTunica adventitia:Tunica adventitia: a fibrous coat of loose connective tissuea fibrous coat of loose connective tissue

StomachStomach

---dilated part---dilated part---store food temporarily---store food temporarily---digest food partially to form a semi-flu---digest food partially to form a semi-flu

id mass, termed chymeid mass, termed chyme---absorb part of water and ions---absorb part of water and ions

Stomach (regions)Stomach (regions)

• Cardia (Cardiac junction)Cardia (Cardiac junction)– Surrounds esophageal entranceSurrounds esophageal entrance

• Fundic stomach defined histologiFundic stomach defined histologically includescally includes– FundusFundus

– BodyBody

• Pylorus (Pyloric junction)Pylorus (Pyloric junction)– Pylorus is continuous with the duoPylorus is continuous with the duo

denumdenum

• MucosaMucosa– Epithelium (simple columnar mucus-secreting)Epithelium (simple columnar mucus-secreting)

– Lamina propria (gastric glands of different types)Lamina propria (gastric glands of different types)

– Muscularis mucosae (Smooth muscle)Muscularis mucosae (Smooth muscle)

• SubmucosaSubmucosa– Loose C.T. no glandsLoose C.T. no glands

• Muscularis externaMuscularis externa inner oblique, middle circular, outer longitudinalinner oblique, middle circular, outer longitudinal

• Tunica adventitiaTunica adventitia– Mostly serosaMostly serosa

Stomach Histology OverviewStomach Histology Overview

mucosamucosa• RugaeRugae

– Longitudinal folds of mucosaLongitudinal folds of mucosa• A mucosal fold contains submucosaA mucosal fold contains submucosa

• Gastric pits: small depressions, 3-5 gastric gland open iGastric pits: small depressions, 3-5 gastric gland open into the bottomnto the bottom

• Diffuse lymphoid tissue and nodules may be presentDiffuse lymphoid tissue and nodules may be present

mucosa

Rugae in the stomachRugae in the stomach

Mucosa

Muscularis mucosa

Submucosa

Muscularis externa

Rugae

Cross section of gastric pitsCross section of gastric pits

Simple columnar epitheliumGastric pit

Laminia propria between pits

①①epitheliumepithelium: simple colu: simple columnar epitheliummnar epithelium

• surface mucous cell: surface mucous cell: -tall columnar -tall columnar -ovoid, basally-located nuclei-ovoid, basally-located nuclei-apical mucin granule-apical mucin granule-tight junction-tight junction

The mucus is secreted on to the eThe mucus is secreted on to the epithelial surface to form a pithelial surface to form a barrbarrier layerier layer which protects it fro which protects it from injury by ingested substance m injury by ingested substance and the stomach’s own secretiand the stomach’s own secretion of acid and enzymes.on of acid and enzymes.

②②lamina proprialamina propria: :

CT contains fibroblast, LC, plasma cell, mast ceCT contains fibroblast, LC, plasma cell, mast cell and eosinophil, smooth musclell and eosinophil, smooth muscle

• gastric gland (fundic gland)-oxyntic glandgastric gland (fundic gland)-oxyntic gland

• cardiac gland: mucous glandcardiac gland: mucous gland

• pyloric gland: mucous glandpyloric gland: mucous gland

* * Fundic glandFundic gland --long, branched or unbranched glandlong, branched or unbranched gland

Three part of gland:Three part of gland:

The neckThe neck

The bodyThe body

The baseThe base

Five type cells are foundFive type cells are found::

Chief cellsChief cells （主细胞）（主细胞）

Parietal cellsParietal cells （壁细（壁细胞）胞）

Mucous neck cellsMucous neck cells

Stem cellsStem cells

Enterendocrine cellsEnterendocrine cells

neck

body

chief cellchief cell or zymogenic cell or zymogenic cell---structure: ---structure: LM: LM: • columnar columnar • Round, basally-located NucleusRound, basally-located Nucleus• cytoplasm: cytoplasm: /basal-basophilic/basal-basophilic /apical-zymogen granules/apical-zymogen granules

EM: EM: RER, Golgi complexRER, Golgi complex

---function---function: :

secret pepsinogen (the precursor secret pepsinogen (the precursor of pepsin)of pepsin)

parietal cellparietal cell or oxyntic cell or oxyntic cell

---structure:---structure:

LM: LM:

• large, pyramidal or sphericallarge, pyramidal or spherical

• round centrally-located nucleusround centrally-located nucleus

• eosinophilic cytoplasmeosinophilic cytoplasm

EM:EM:

• intracellular secretory canaliculuintracellular secretory canaliculus-invaginationss-invaginations

• tubulovesicular systemtubulovesicular system

• mitochondriamitochondria

---function: ---function:

1. secret hydrochloric acid (HCl) 1. secret hydrochloric acid (HCl) synthesis processes of HCl: synthesis processes of HCl:

in intracellular secretory canaliculusin intracellular secretory canaliculus

• HH++ K K++ -ATP pump: get H -ATP pump: get H++ from cell from cell

• ClCl-- channel: get Cl channel: get Cl-- from blood from blood

• HH++ +Cl +Cl--→HCl→HCl

function of HCl:function of HCl:

• pepsinogen→pepsinpepsinogen→pepsin

• kill the bacteriakill the bacteria

mucous neck cellmucous neck cell• less, neck partless, neck part• pale stain in HE stainpale stain in HE stain• secrete mucussecrete mucus

stem cellstem cell undifferentiated cellundifferentiated cell

enterendocrine cellenterendocrine cell • ECL cell: secreting histamine, promote secretion of paECL cell: secreting histamine, promote secretion of pa

rietal cellrietal cell• D cell: secreting somatostatin, inhibit the secretion of pD cell: secreting somatostatin, inhibit the secretion of p

arietal cellarietal cell

• Epithelial transitionEpithelial transition

– Stratified Squamous nStratified Squamous nonkeratinized to simple onkeratinized to simple columnarcolumnar

Cardiac JunctionCardiac Junction

Small intestineSmall intestine

Duodenum – first region, only about 25cm long, Duodenum – first region, only about 25cm long,

Jejunum – second region is roughly 2.5m longJejunum – second region is roughly 2.5m long

Ileum – last region is roughly 3.5m longIleum – last region is roughly 3.5m long

Primary functionsPrimary functions• Transport food from stomach to Large intestineTransport food from stomach to Large intestine• Secretion of digestive enzymes to facilitate digestion of food substancesSecretion of digestive enzymes to facilitate digestion of food substances• Absorption of food substances into blood and lymph vesselsAbsorption of food substances into blood and lymph vessels• Secretion of certain hormonesSecretion of certain hormones

Small Intestine OverviewSmall Intestine Overview

• MucosaMucosa– Epithelium (simple columnar mucus-secreting)Epithelium (simple columnar mucus-secreting)

– Lamina propria (intestinal glands)Lamina propria (intestinal glands)

– Muscularis mucosae (Smooth muscle)Muscularis mucosae (Smooth muscle)

• SubmucosaSubmucosa– loose C.T. (contain duodenal glands in the duodenum)loose C.T. (contain duodenal glands in the duodenum)

• Muscularis externaMuscularis externa inner circular, outer longitudinalinner circular, outer longitudinal

• Tunica adventitiaTunica adventitia– serosa (except for the duodenum)serosa (except for the duodenum)

Special structure of mucosaSpecial structure of mucosa

• Plicae circulares Plicae circulares – Mucosa and submucosa are arranged in permanent, Mucosa and submucosa are arranged in permanent,

circular mucosal foldscircular mucosal folds

• Intestinal villiIntestinal villi– Mucosal projections covered by epithelium and contMucosal projections covered by epithelium and cont

aining only lamina propriaaining only lamina propria

• Crypt or intestinal glandsCrypt or intestinal glands– Surrounded by lamina propriaSurrounded by lamina propria

– Extend to the muscularis mucosaeExtend to the muscularis mucosae

Plicae circularesPlicae circulares

VilliVilli

Plicae circularesPlicae circulares

villivilli

• EpitheliumEpithelium (Simple columnar) (Simple columnar)– Absorptive cellsAbsorptive cells

• Numerous, regular microvilli form striated-borderNumerous, regular microvilli form striated-border

• Well formed junctional complexWell formed junctional complex

Plicae circulares, villi and microvilli are serve to increase the surface arePlicae circulares, villi and microvilli are serve to increase the surface area of the small intestine by as much as 600-folda of the small intestine by as much as 600-fold

surface coat: a layer of glycoprotein filament, protect the underlying cellsurface coat: a layer of glycoprotein filament, protect the underlying cells from mucolytic and proteolytic agents from mucolytic and proteolytic agent

– Goblet cellsGoblet cells :secrete mucus to lubricate and protect the epithel :secrete mucus to lubricate and protect the epitheliumium

– Enteroendocrine cells: Enteroendocrine cells: produce hormonesproduce hormones

striated-striated-borderborder

microvillimicrovilli

lamina propria:lamina propria:

LCT, macrophage, plasma cell LCT, macrophage, plasma cell and eosinophil and mast celland eosinophil and mast cell

central lacteal:central lacteal: lymphatic vessel, absorlymphatic vessel, absor

b fatb fat

Crypt or small intestinal glandCrypt or small intestinal gland:: the invagination of epithelium into lamina propria the invagination of epithelium into lamina propria

• absorptive cellabsorptive cell

• goblet cellgoblet cell

• endocrine cellendocrine cell

• stem cellstem cell

• Peneth cellPeneth cell

Peneth cellPeneth cell::LM: LM:

-pyramidal in shape, locate in bas-pyramidal in shape, locate in basal portion of the glands, in groal portion of the glands, in groupsups

-apical: acidophilic granules- cont-apical: acidophilic granules- contain defensin (cryptdin), Lysozyain defensin (cryptdin), Lysozymeme

EM: EM:

-protein-secreting cell feature-protein-secreting cell feature

Function: related to immune funcFunction: related to immune function, anti-bacterial activitytion, anti-bacterial activity

Large intestineLarge intestine

---Consists of:---Consists of:

-cecum-cecum

-ascending colon-ascending colon

-transverse colon-transverse colon

-descending colon-descending colon

-sigmoid colon-sigmoid colon

-rectum-rectum

-anal canal-anal canal

--- function:--- function:

absorb water and ions absorb water and ions

• MucosaMucosa– No villi or plicae circularesNo villi or plicae circulares

– Glands are longer than in small Glands are longer than in small intestineintestine

– Single columnar epithelium conSingle columnar epithelium contain numerous goblet cells but atain numerous goblet cells but absorptive cells are still presentbsorptive cells are still present

– Occasional solitary lymph noduOccasional solitary lymph nodulesles

– At anal junction there is an abrAt anal junction there is an abrupt transition to stratified squaupt transition to stratified squamous non-keratinized epitheliumous non-keratinized epithelium. m.

• SubmucosaSubmucosa– Similar to small intestine eSimilar to small intestine e

xcept nerve plexus are moxcept nerve plexus are more easily found herere easily found here

• Muscularis externaMuscularis externa– Inner circular layer is eviInner circular layer is evi

dentdent

– Outer longitudinal layer fOuter longitudinal layer forms three bands, the taenorms three bands, the taenia coliia coli

• Adventitia Adventitia – Both serosa and fibrosa arBoth serosa and fibrosa ar

e founde found

• Mucosa is like the colon exceptMucosa is like the colon except– Numerous lymph nodules are present in the youngNumerous lymph nodules are present in the young

– These decrease with ageThese decrease with age

– They break up the muscularis mucosae so that it is dThey break up the muscularis mucosae so that it is difficult to findifficult to find

– The glands are also often not very evident.The glands are also often not very evident.

• Submucosa and muscularis externa are like the Submucosa and muscularis externa are like the rest of the colonrest of the colon

Appendix Appendix (study by yourself)(study by yourself)

AppendixAppendix