1. Digestive tract

2. ---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

3. Components of digestive tract ---oral cavity
---pharynx
---esophagus
---stomach
---small intestine
---large intestine

4. General plan of digestive tract
---Except for oral cavity and pharynx, all other organs share a similar histological plan

5. General Plan Mucosa(内膜） Submucosa（内膜下层） Epithelium
Lamina propria (may contain glands)
Muscularis mucosae (Smooth muscle)
Submucosa（内膜下层）
Loose C.T. may contain glands
Meissner’s autonomic nerve plexus

6. Muscularis externa（肌层）
Inner circular
Myenteric (Auerbach’s) autonomic nerve plexus
Outer longitudinal
Tunica adventitia（外膜）
Fibrosa or serosa (covered by mesothelium)

7. Esophagus Passage way for food from the pharynx to the stomach mucosa:
epithelium: stratified squamous epithelium
lamina propria: compact CT
muscularis mucosa: longitudinal
arranged smooth muscle
submucosa:
LCT
esophageal gland: mucous gland

8. Muscularis externa:
inner circular and outer longitudinal
upper 1/3: skeletal muscle
middle 1/3: mixed of skeletal muscle and smooth muscle
lower 1/3: smooth muscle
Tunica adventitia:
a fibrous coat of loose connective tissue

10. Stomach ---dilated part ---store food temporarily
---digest food partially to form a semi-fluid mass, termed chyme
---absorb part of water and ions

11. Stomach (regions) Cardia (Cardiac junction)
Surrounds esophageal entrance
Fundic stomach defined histologically includes
Fundus
Body
Pylorus (Pyloric junction)
Pylorus is continuous with the duodenum

12. Stomach Histology Overview
Mucosa
Epithelium (simple columnar mucus-secreting)
Lamina propria (gastric glands of different types)
Muscularis mucosae (Smooth muscle)
Submucosa
Loose C.T. no glands
Muscularis externa
inner oblique, middle circular, outer longitudinal
Tunica adventitia
Mostly serosa

13. mucosa Rugae Longitudinal folds of mucosa
A mucosal fold contains submucosa
Gastric pits: small depressions, 3-5 gastric gland open into the bottom
Diffuse lymphoid tissue and nodules may be present
mucosa

14. Rugae in the stomach
Mucosa
Muscularis mucosa
Submucosa
Muscularis externa
Rugae

15. Simple columnar epithelium Gastric pit Laminia propria between pits
Cross section of gastric pits
Simple columnar epithelium
Gastric pit
Laminia propria between pits

16. ①epithelium: simple columnar epithelium
surface 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 stomach’s own secretion of acid and enzymes.

17. ②lamina propria:
CT contains fibroblast, LC, plasma cell, mast cell and eosinophil, smooth muscle
gastric gland (fundic gland)-oxyntic gland
cardiac gland: mucous gland
pyloric gland: mucous gland

18. * Fundic gland
-long, branched or unbranched gland

19. Five type cells are found: Chief cells（主细胞） Parietal cells（壁细胞）
Three part of gland:
The neck
The body
The base
Five type cells are found:
Chief cells（主细胞）
Parietal cells（壁细胞）
Mucous neck cells
Stem cells
Enterendocrine cells
neck
body

20. chief cell or zymogenic cell ---structure: LM:
columnar
Round, basally-located Nucleus
cytoplasm:
/basal-basophilic
/apical-zymogen granules
EM:
RER, Golgi complex
---function:
secret pepsinogen (the precursor of pepsin)

21. parietal cell or oxyntic cell ---structure: LM:
large, pyramidal or spherical
round centrally-located nucleus
eosinophilic cytoplasm
EM:
intracellular secretory canaliculus-invaginations
tubulovesicular system
mitochondria

22. 1. secret hydrochloric acid (HCl)
---function:
1. secret hydrochloric acid (HCl)
synthesis processes of HCl:
in intracellular secretory canaliculus
H+ K+ -ATP pump: get H+ from cell
Cl- channel: get Cl- from blood
H+ +Cl-→HCl
function of HCl:
pepsinogen→pepsin
kill the bacteria

23. mucous neck cell stem cell enterendocrine cell
less, neck part
pale stain in HE stain
secrete mucus
stem cell
undifferentiated cell
enterendocrine cell
ECL cell: secreting histamine, promote secretion of parietal cell
D cell: secreting somatostatin, inhibit the secretion of parietal cell

24. Cardiac Junction Epithelial transition
Stratified Squamous nonkeratinized to simple columnar

25. Small intestine Duodenum – first region, only about 25cm long,
Jejunum – second region is roughly 2.5m long
Ileum – last region is roughly 3.5m long
Primary functions
Transport food from stomach to Large intestine
Secretion of digestive enzymes to facilitate digestion of food substances
Absorption of food substances into blood and lymph vessels
Secretion of certain hormones

26. Small Intestine Overview
Mucosa
Epithelium (simple columnar mucus-secreting)
Lamina propria (intestinal glands)
Muscularis mucosae (Smooth muscle)
Submucosa
loose C.T. (contain duodenal glands in the duodenum)
Muscularis externa
inner circular, outer longitudinal
Tunica adventitia
serosa (except for the duodenum)

27. Special structure of mucosa Plicae circulares
Mucosa and submucosa are arranged in permanent, circular mucosal folds
Intestinal villi
Mucosal projections covered by epithelium and containing only lamina propria
Crypt or intestinal glands
Surrounded by lamina propria
Extend to the muscularis mucosae

28. Plicae circulares
Villi

29. Plicae circulares
villi

30. Epithelium (Simple columnar)
Absorptive cells
Numerous, regular microvilli form striated-border
Well 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 epithelium
Enteroendocrine cells: produce hormones

31. striated-border

32. microvilli

33. lamina propria:
LCT, macrophage, plasma cell and eosinophil and mast cell
central lacteal:
lymphatic vessel, absorb fat

34. Crypt or small intestinal gland:
the invagination of epithelium into lamina propria
absorptive cell
goblet cell
endocrine cell
stem cell
Peneth cell

35. Peneth cell:
LM:
-pyramidal in shape, locate in basal portion of the glands, in groups
-apical: acidophilic granules- contain defensin (cryptdin), Lysozyme
EM:
-protein-secreting cell feature
Function: related to immune function, anti-bacterial activity

36. Large intestine ---Consists of: -cecum -ascending colon
-transverse colon
-descending colon
-sigmoid colon
-rectum
-anal canal
--- function:
absorb water and ions

37. Mucosa No villi or plicae circulares
Glands are longer than in small intestine
Single columnar epithelium contain numerous goblet cells but absorptive cells are still present
Occasional solitary lymph nodules
At anal junction there is an abrupt transition to stratified squamous non-keratinized epithelium.

38. Submucosa Muscularis externa Adventitia
Similar to small intestine except nerve plexus are more easily found here
Muscularis externa
Inner circular layer is evident
Outer longitudinal layer forms three bands, the taenia coli
Adventitia
Both serosa and fibrosa are found

39. Appendix (study by yourself)
Mucosa is like the colon except
Numerous lymph nodules are present in the young
These decrease with age
They break up the muscularis mucosae so that it is difficult to find
The glands are also often not very evident.
Submucosa and muscularis externa are like the rest of the colon

40. Appendix