1. Histology of The GIT

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

3. 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  ??

4. 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  ??

5. 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

6. Auerbach’s Myernteric Plexus

7. 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

8. 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:

9. 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

10. 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

11. 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

12. 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)

13. (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

14. 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

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

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

17. 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

18. 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

19. Electron Micrograph for Villi in S.I.

20. 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

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

22. 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

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

25. Regional Differences in The Small Intestine

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

27. 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 ??

28. 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.

30. 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

32. 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)

33. 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