1. Digestive tract Li Zhong Jie（李仲杰）, Ph. D
School of Medicine,Zhejiang University

2. ---Digestive system function:
Digestive tract
Digestive gland
---Digestive system function:
This system is responsible for the mechanical and chemical break down 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
The digestive system is a long, tortuous, hollow tube. It engages in many function such as propulsion, secretion, absorption, excretion ,immunologic protection, and hormone production.

3. The Digestive Process Ingestion Propulsion (movement of food)
Taking in food through the mouth
Propulsion (movement of food)
Swallowing
Peristalsis – propulsion by alternate contraction & relaxation
Mechanical digestion
Chewing
Churning in stomach
Mixing by segmentation
Chemical digestion
Carbohydrates, Fat, and Proteins are broken down by enzymes.
Absorption
Transport of digested end products into blood and lymph in wall of canal
Defecation
Elimination of indigestible substances from body as feces

4. Chemical digestion
--- Complex food molecules (carbohydrates, proteins and lipids) broken down into chemical building blocks (simple sugars, amino acids, and fatty acids and glycerol)
--- Carried out by enzymes secreted by digestive glands into lumen of the alimentary canal

5. Components of digestive tract ---oral cavity
---pharynx
---esophagus
---stomach
---small intestine
---large intestine
---rectum and anus

6. General plan of digestive tract
---Except for oral cavity and pharynx, all other organs share a similar histological plan
Mucosa
Submucosa
Muscularis externa
Adventitia
from lumen (inside) out

7. Inner layer: the mucosa* (mucous membrane)
Three sub-layers
epithelium
lamina propria (may contain glands)
Muscularis mucosae (Smooth muscle) *

8. Mucosa 1. Epithelium -------two types
stratified squamous & simple columnar epith.
2. Lamina propria
LCT. contained small glands，blood & lymph
capillaries. mucosa-associated lymphoid tissue
3. Muscularis mucosa
inner circular / outer longitudinal layer
of smooth muscle cells.
surface
depth

9. the submucosa* * LCT. with small blood / lymphatic vessels;
* glands only in the
esophagus and
duodenum
Submucosal ( Meissner’s autonomic) nerve plexus *

10. Plica
*a fold of mucosa and submucosa
*longitudinal/circular form. GI

11. the muscularis externa*
Two layers of smooth muscle responsible for peristalsis and segmentation
Inner circular layer (circumferential)
Myenteric (Auerbach’s autonomic) nerve plexus
Outer longitudinal layer: ---shortens gut *

12. Smooth muscle Muscles are spindle-shaped cells One central nucleus
Grouped into sheets: often running perpendicular to each other
Peristalsis
No striations (no sarcomeres)
Contractions are slow, sustained and resistant to fatigue
Does not always require a nervous signal: can be stimulated by stretching or hormones

13. Adventitia *the outmost layer formed by CT with two types: fibrosa:
CT blending with
surrounding structure
serosa:
CT + mesothelium
（for example, peritoneum）

14. Enteric nervous system:
Mainly components:
100 million neurons! (as many as the spinal cord)
unmyelinated nerve fibers
controlling the muscles, glands and having sensory info
Muscularis external: Myenteric nerve plexus
Submucosa: Submucosal nerve plexus

15. * Myenteric (Auerbach’s) plexus : regulate the movement of SM
inner circular
Nerve plexus
outer longitudinal

16. Esophagus
mucosa
submucosa
muscularis
adventitia

17. Esophagus Passage way for food from the pharynx to the stomach mucosa:
epithelium: stratified squamous epithelium
lamina propria: compact CT contain simple tubular glands
muscularis mucosa: longitudinal
arranged smooth muscle
At EG junction – thin simple columnar
epithelium
submucosa:
LCT
esophageal gland: mucous gland
---acidic mucin

18. 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

19. When empty, mucosa and submucosa lie in longitudinal folds

20. Cardiac Junction Epithelial transition
---Stratified Squamous nonkeratinized to simple columnar
It is clinically important, as it is the most site of esophageal carcinoma.

21. Stomach ---widest part of alimentary canal
---Temporary storage and mixing – 4 hours
---digest food partially to form a semi-fluid mass, termed chyme
---absorb part of water and ions
Water, electrolytes, some drugs like aspirin and alcohol (absorbed through stomach)

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

23. plica: longitudinal folds on internal surface (helps distensibility)

24. Structural Characteristic of Stomach
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

25. mucosa plica 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
Gastric pit

26. plica in the stomach
Mucosa
Muscularis mucosa
Submucosa
Muscularis externa
plica

27. *gastric pits ①epithelium: simple columnar epithelium
surface mucous cell:
---tall columnar
---ovoid, basally-located nuclei
---apical mucin granule
---tight junction
*gastric pits

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

29. ②lamina propria:
CT contains fibroblast, LC, plasma cell, mast cell and eosinophilic smooth muscle
*Gastric gland:
fundic gland:oxyntic gland
cardiac gland: mucous gland
pyloric gland: mucous gland

30. * Fundic gland
---long, straight, branched or unbranched gland

31. Three part of gland:
The neck
The body
The base
Five type cells are found:
Chief cells
Parietal cells
Mucous neck cells
Stem cells
endocrine cells

32. Fundic gland

33. parietal cell or oxyntic cell ---structure:
LM:
large, pyramidal or spherical
round centrally-located nuclei
eosinophilic cytoplasm

34. intracellular secretory canaliculus (active stage)
EM:
intracellular secretory canaliculus (active stage)
tubulovesicular system(resting stage)
a few RER, Golgi apparatus and more mitochondria
Trench –like infoldings of apical cell membranes form a ramifying network of narrow channels- secretory canaliculi. They occur throughout the cytoplasm and near the nucleus and open into glandular lumina. Cannliculi are lined by many densely packed microvilli.
secreting stage
Resting stage

35. Ultrastructural model of Parietal cell
intracellular secretory canaliculus
tubulovesicular system
microvilli
nucleus
mitochondria
Resting stage
Secreting stage
Ultrastructural model of Parietal cell GI

36. intracellular secretory canaliculus
Secreting stage
interconvert
Resting stage GI
tubulovesicular system

37. Function of parietal cell (oxyntic cell)
*secreting hydrochloride acid
---providinng acidic condition for activation of the pepsinogen.
---killing bacteria except for helicobacter pylori .
*producing intrinsic factor
---binding with vitamin B12, aiding its absorption
in the small intestine.
---helping production of red blood cells.
an deficiency of VB12
result in Addison’s anaemia GI

38. chief cell ( zymogenic cell) ---structure: LM:
columnar
Round, basally-located Nuclei
cytoplasm:
/basal-basophilic
/apical-zymogen granules

39. EM:
RER, Golgi apparatus
---function: secret pepsinogen(the precursor of pepsin)

40. Function of chief cell secreting pepsinogen (inactive) pepsin (active)
protein peptides
(acid environment) GI

41. Fundic gland
内分泌细胞
主细胞
颈粘液细胞
壁细胞

42. chief cell
parietal cell
secret hydrochloric acid
secret intrinsic factor
function: secret pepsinogen

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

44. * Mucous-HCO3 barrier structure :
mostly of glycoproteins rich in carbohydrates and bicarbonate ions
mm thick mucous
The pH of the surface is usually

45. * Mucous-HCO3 barrier function :
The mucus( bicarbonate-buffered 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.
acid-base neutralization
H+ + HCO3- → H2CO3 →H2O + CO2 ↑
bicarbonatase

46. 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 nutrient substances into blood and lymph vessels
Secretion of certain hormones

47. 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

48. villi
Plicae circulares

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

50. Structural Characteristic of small intestine
Mucosa
Epithelium (simple columnar)
Lamina propria (intestinal glands)
Muscularis mucosae (Smooth muscle)
Submucosa
loose C.T. (contain duodenal glands in the duodenum)
Muscularis externa
inner circular, Myenteric (Auerbach’s) plexus , outer longitudinal
Tunica adventitia
serosa (except for the duodenum)

52. Lymph Nodules

53. Epithelium (Simple columnar)
Absorptive cells
A tall columnar cell with ovoid nucleus
Numerous, regular microvilli form striated-border
Well formed junctional complex
*cell coat: a layer of glycoprotein film, protect the underlying cells
from mucolytic and proteolytic agent
Goblet cells :secrete mucus to lubricate and protect the epithelium
Enteroendocrine cells: produce hormones

54. striated-border

55. simple columnar cells
microvilli

56. lamina propria: LCT contains network of blood and lymph capillaries
- transport sugar and amino acid into blood to liver via hepatic portal vein
- delivers lipid into lymph
*central lacteal:
lymphatic vessel,
absorb lipid

57. Small intestine glands
Core of villus
epithelium
villus
Smooth m.f.
gland A
gland L V
Model
H.E. staining
Longitudinal section of small intestine

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

59. Peneth cell: Structure: LM:
---pyramidal in shape, locate in basal portion of the glands, in groups
---apical: acidophilic granules- contain defensin, lysozyme
EM:
---protein-secreting cell feature
Function: secreting defensin, lysozyme which involved in the control of infection.

60. Muscularis externa Inner circular SM Myenteric plexus
Outer longitudinal SM

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

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

63. 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

64. Appendix

65. Appendix Mucosa ---Surface epith. with few goblet cells. Submucosa
---Numerous lymph nodules are present in in the lamina propria and the submucosa .
---rare intestinal glands and muscularis mucosa usually incomplete.
Submucosa
thin muscularis
Serosa

66. Review and exercise
1. Compare the mucosal structure of stomach with that of esophagus, small intestine and large intestine.
2. Describe the fine structure and ultra-structure of the parietal cell and chief cell in the gastric gland.
3. Describe the different formation of villi and plicae in small intestine.
4. Describe the structure of mucosa of the digestive tract.

67. Thanks for your attention!