Download Document

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. & 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
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
Mostly in the ?? Of the gland
Secrete enzymes (pepsinogen & g. lipase)
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
Gastric glands:
highly coiled
mostly mucous cells
few parietal
no chief cells
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.
 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 ??
*  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