Download 11. digestive tract--

Digestive tract
---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
Components of digestive tract
---oral cavity
---pharynx
---esophagus
---stomach
---small intestine
---large intestine
General plan of digestive tract
---Except for oral cavity and pharynx, all other organs share
a similar histological plan
General Plan
• Mucosa(内膜）
– 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
• Muscularis externa（肌
层）
– Inner circular
– Myenteric (Auerbach’s)
autonomic nerve plexus
– Outer longitudinal
• Tunica adventitia（外膜）
– Fibrosa or serosa (covered
by mesothelium)
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
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
Stomach
---dilated part
---store food temporarily
---digest food partially to form a semifluid mass, termed chyme
---absorb part of water and ions
Stomach (regions)
• Cardia (Cardiac junction)
– Surrounds esophageal
entrance
• Fundic stomach defined
histologically includes
– Fundus
– Body
• Pylorus (Pyloric junction)
– Pylorus is continuous with
the duodenum
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
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
Rugae in the stomach
Mucosa
Muscularis mucosa
Rugae
Submucosa
Muscularis externa
Cross section of gastric pits
Simple columnar epithelium
Gastric pit
Laminia propria between pits
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.
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
* Fundic gland
-long, branched or unbranched gland
Three part of gland:
The neck
neck
body
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
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)
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
---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
mucous neck 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
Cardiac Junction
• Epithelial transition
– Stratified Squamous
nonkeratinized to
simple columnar
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
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)
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
Plicae circulares
Villi
Plicae circulares
villi
• 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
striated-border
microvilli
lamina propria:
LCT, macrophage, plasma
cell and eosinophil and
mast cell
central lacteal:
lymphatic vessel,
absorb fat
Crypt or small intestinal gland:
the invagination of epithelium into lamina propria
• absorptive cell
• goblet cell
• endocrine cell
• stem cell
• Peneth cell
Peneth cell:
LM:
-pyramidal in shape, locate in
basal portion of the glands, in
groups
-apical: acidophilic granulescontain defensin (cryptdin),
Lysozyme
EM:
-protein-secreting cell feature
Function: related to immune
function, anti-bacterial activity
Large intestine
---Consists of:
-cecum
-ascending colon
-transverse colon
-descending colon
-sigmoid colon
-rectum
-anal canal
--- function:
absorb water and ions
• 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.
• Submucosa
– 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
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
Appendix