Histology of The GIT

Histology of The GIT 4 main layers: 1- Mucosa 2. Submucosa 3. Muscularis Externa 4- Serosa or Adventitia * Regional modifications & specializations

Mucosa 3 layers 1. Epithelium Str. Sq.  simp. Column.  simp. cuboidal  str. Sq. 2. Lamina Propria: L.C.T.  richly vascularized 3. Muscularis Mucosa: 2 zones of Sm. M.: Inner  ?? Outer  ??

Submucosa D. ir. C. T. Contains bld Submucosa D. ir. C.T. Contains bld. & lymph vessels Muscularis Externa Inner  ?? sm. m. Outer  ?? Sm. m. *responsible for peristaltic activity Serosa or Adventitia Thin C.T. Layer - If covered by visceral peritoneum  ?? - If not  ??

Enteric Nervous System (ENS) (Brain of The Gut) The GIT self-contained nervous system that extends from esophagus to anus (100 million neurons = S.C.) Controls: 1. Secretory fxn. of GI gland 2. Motility 2 parts (Plexuses): Meissener’s submucosal plexus - in submucosa - secretory fxn. & mucosal movements Auerbach’s myenteric plexus - between ?? & ?? Layers of ?? - peristaltic motility

Auerbach’s Myernteric Plexus

Esophagus Mucosa - Str. Sq. nonk. (usually collapsed) Interspersed in between  Langerhans cells (phagocytes) - Lamina Propria is unremarkable - Muscularis Mucosa Only 1 layer of ?? Sm. m. fibers

Esophagus Submucosa - houses esophageal glands * Esophgus & ?? are the only 2 regions in GIT with glands in submucosa Muscularis Externa - 2 layers (in-circ & out-longi.) - Mixed Sk & Sm m.  1/3: Middle 1/3:  1/3:

Stomach Epithelium Simp. Colum. Epith.  Surface lining (mucous) cells Invaginate into mucosa to form ?? Lined with thick mucus layer  visible mucus Fxn. is to ?? Display apical microvilli that contain secretory granules

Stomach Lamina Propria Occupied by  15 million gastric glands Glands extend from MM to the base of ?? Each gland is composed of 5 types of cells

2. Regenerative (Stem) Cells 1. Mucous Neck Cells Resemble ?? Cells 2. Regenerative (Stem) Cells Very few Do not have many organelles, but very rich in ?? Fxn.: proliferate to replace other cells

3. Parietal (Oxyntic) Cells Pyramidal in shape Mostly in the ?? Of the gland Produce HCl & intrinsic factor (?) 4. Chief (Zymogenic) Cells Columnar cells with basophilic cytoplasm Secrete enzymes (pepsinogen & g. lipase)

(Enteroendocrine Cells) 5. DNES Cells (Enteroendocrine Cells)  13 different types  specialized in secreting a specific agent * Most common is G cells G cells: Located in the base of the gland Secrete ??  Stimulates stem cells

Differences in the Mucosa of Cardiac & Pyloric Regions Cardiac Region: Shallow gastric pits Gastric glands: coiled base only mostly surface lining epith. few parietal cells no chief cells Pyloric Region: Deep gastric pits highly coiled mostly mucous cells few parietal

Stomach Muscularis Mucosa 3 layers: Inner  circular Outer  longitudinal Outermost  circular (Not always evidant)

Stomach Submucosa D. Ir. C. T. Muscularis Externa 3 layers of Sm. m. Innermost  oblique Middle  circular  forms pyloric sphincter Outer  longitudinal

Small Intestine 3 Modifications of luminal surface to  increase surface area 1. Plicae Circulares Transverse folds of mucosa & submucosa Permanent fixtures of s.i.  surface area 2 to 3 times

2. Villi finger-like projections of L. P. & epith 2. Villi finger-like projections of L.P. & epith.  surface area x10 core of each villus contains  a blind end lymph vessel = Lacteal Intestinal glands (Crypts of Lieberkuhn) open into their bases (in between) 3. Microvilli modifications of apical plasmamembrane of epith. Cells (Brush Border)  surface area x20

Electron Micrograph for Villi in S.I.

Epithelium of Small Intestine Composed of: 1. Surface absorptive cells:  numerous tall columnar cells with brush border Fxn.: terminal digestion and absorption of water & nutrients  into L.P. 2. Goblet cell: Unicellular glands secrete mucinogen mucinogen  mucin  mucus

Epithelium of Small Intestine Composed of: 3. DNES cells: 1% of total cells 4. M (Microfold) cells: squamous-like cells near lymph nodules (Phagocytes)

Lamina Propria of Small Intestine Contains intestinal glands: Crypts of Lieberkühn Simple tubular glands that open into intervillar spaces as perforations Composed of : - Surface absorptive cells - Goblet cells - DNES cells - Stem cells - Paneth cells

Paneth Cells Pyramidal cells At the bottom of the crypts Contain large eosinophilic granules Secrete antibacterial agent = lysozyme

Regional Differences in The Small Intestine

Duodenum Broader, taller &  numerous villi  Goblet cells Brunner’s glands in submucosa

Brunner’s Glands Branched, tubuloalveolar glands Only in duodenal submucosa Ducts penetrate MM to open into ?? Secrete: mucous alkaline fluid (rich in HCO3-)  nutralize the acidic chyme Urogastrone (human epidermal G.F.)   production of ??

Jejunum Narrower, shorter and sparser villi than Jejunum Narrower, shorter and sparser villi than ?? *  goblet cell Ileum Rare villi Rich in goblet cells * Peyer’s Patches clusters of lymph nodules in L.P.

Large Intestine No villi  Crypts of Lieberkühn (except no ?? Cells) Epithelium: Surface absorptive cells most numerous Goblet cells  from cecum to sigmoid colon DNES cells Stem cell

Large Intestine Muscularis Externa: Inner  circular Outer  longitudinal : arranged into 3 fascicles of muscles  Taeniae coli T.C. are in constant contraction  puckers L.I. into saccules (haustra)

Anal Canal Epithelium Simple cuboidal: Rectum  pectinate line (int. anal sphincter) Str. Sq. nonk.: pectinate line  ext. anal sphincter Str. Sq. Kerat.: after ext. sphincter Muscularis Externa: Inner circular layer thickened at Pectinate line to form ?? Recto-anal junction