Download Chapter 11 Digestive tract

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Chapter 11 Digestive tract
Lyu Zhengmei
Department of Histology and Embryology,
Anhui Medical University
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introdction
Digestive tract (DT)
and Digestive glands
===Digestive system:
Functions of DT:
Obtain molecules from
ingested food.
A protective barrier for the
body.
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Functions
Oral cavity
Ingestion and Initial fragmentation
esophagus
Conduct food from oral to stomach
Stomach
Complete fragmentation and initial digestion
Duodenum
Get enzymes from pancreas and liver
Jejunum and Ileum
Large intestine
Complete digestion and main absorption
Absorption of Water and ions
Elimination of waste products
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Part One
Oral Cavity and Related
structures
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Oral cavity
 The oral cavity extend from lips to pharynx.
 lined by nonkeratinized stratified squamous epi., except
the gum and hard palate (keratinized).
 The wall of the oral cavity is made up of CT, muscles and
bone.
 The oral cavity contains
the lips, the teeth, the
tongue and salivary glands.
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Papillae

Filiform papillae

Fungiform papillae

Circumvallate
papillae
CV
Foliate
Fg
FL
a). Filiform papillae: The most numerous. Present over entire
surface. small and conical in shape.
b). Fungiform papillae: resemble mushrooms, a narrow stalk and a
dilated upper part.
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c). Circumvallate papillae: The largest papillae.
CV is encircled by a deep cleft.
 The epthelium contains numerous of taste buds.
 Underlying of the mucosa, there are serous glands
CV
Foliate
Fg
FL
VE: serous glands(von Ebner’s)
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Taste bud
10,000 TBs in your mouth, present in the epi. of fungiform
papillae, circumvallate papillae, etc.

a onion-shaped structure made up of modified epithelial cells.

a small cavity that opens to the surface through a taste pore.
The cells in TB are of 3 basic
types. Receptor cells or taste cells,
supporting cells, which have
microvilli on the tip of the cells
and basal cells.

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The same taste bud can respond
to 4 types of taste (sweet, sour, salty
and bitter). The sweet and salty is
less sensitive, but bitter is most
sensitive.

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Part two
Esophagus, Stomach
and Intestine
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1. Components
of digestive tract
mucosa
submucosa
muscularis
share a similar histological plan: a hollow tube composed
of a lumen surrounded by a wall.
The wall includes: mucosa, submucosa, muscularis and
adventitia.
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2. General structural details of the wall
1) Mucosa (mucous membrane)
---------Three sublayers
 Epithelium :
stratified squamous epi.
simple columnar epi.
FUNCTION:
A selectively permeable barrier.
• Facilitate the transport and digestion.
• Promote the absorption
•Produce the hormone
•Secret mucus for lubrication and
protection.
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Lamina propria:
LCT rich in BV, LV and
LP
nerves ,lymphoid tissues, glands
Muscularis mucosae :
Except esophagus, 2 sublayers
(Inner circular and outer longitudinal
of smooth muscle).
Function: Promote the movements
of the mucosa and increase its
contact with the food.
LP
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2) Submucosa:
CT .
Submucosa nerve plexus.
3) Muscularis : Smooth muscle cells and
less skeletal muscle cells.
inner circular and outer longitudinal sublayer
 Myenteric nerve plexus
Function: The contraction of muscularis
mucosa
propel and mix the food in digestive tracts.
4) Adventitia
submucosa
Serosa: LCT + mesothelium
Fibrosa: LCT
muscularis
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Part 3
1) Mucosa:
stratified squamous epi
lamina propria
muscularis mucosa:
only a layer of longitudinal
arranged SM
2) Submucosa: CT
esophageal gland:
mucous gland
Esophagus
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3) Muscularis:
inner circular and outer longitudinal

upper portion: only skeletal muscle

middle portion: mixture of
skeletal and smooth muscle

lower end: only smooth muscle
4) Adventitia: fibrosa
Functions:
 Transport food from the mouth
to the stomach.
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Stomach
Functions:

store food temporarily
 initial digestion
 absorb part of water and ion
Structures:
Gross inspection reveals 4
regions:
 fundus,
 cardia,
 body,
 pylorus


Folds or rugae.
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

The wall is composed of 4
layers:
Mucosa, submucosa,
muscularis adventitia.
Mucosa have some special
features .
Mucosa muscularis
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Regions of
the stomach
and their
histological
structure
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I. Mucosa of stomach
① Epithelium:
Surface mucous cell:
Structures:
LM: Tall columnar, ovoid and basallylocated nucleus.
with mucin granules, so cells look empty
with HE staining.
gastric pit: formed by epithelium invaginates
into lamina propria
Functions:
Secreting mucus, which form mucous
barrier
Gastric pit
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② lamina propria:
Gastric pit
Deep to gastric pits,
packed with gastric
glands and scanty CT.
 Here’re 3 types of
gastric gland:
Main gastric gland
cardiac gland
pyloric gland.
muscularis mucosa
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Main gastric glands
Distribution:
Most of the stomach (present
in the body and fundus) except
pylorus and cardia.
Structures:
 Simple or branched tubular glands.
The glands open into gastric pits.
The epithelium of the glands includes chief cells, parietal cells,
neck mucous cells, undifferentiated cells and endocrine cells.
Their distribution is not uniform.
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1. Parietal cell or
oxyntic cell

Distribution:
more numerous in the
upper half of the gland.

Structures:
LM: rounded or
pyramidal with round
and centrally-located
nucleus.
The cytoplasm is
strongly acidophilic.
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EM:
Active cell
Intracellular canaliculus
(IC), which bear microvilli
in the wall. Tubulovesicles
(TV) and Abundant
Mitochondria
Functions:
secrete hydrochloric acid
and produce intrinsic factor.
Resting cell
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Active ce
EM of Parietal cell
Resting cell
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1 Function of Hydrochloric acids
Pepsinogen (chief cells)
hydrochloric acids
Proteins
Pepsin
pH0.9-1.5
Peptides
2 Function of intrinsic factor
Intrinsic factor
Complex
Vitamin B12
production of erythrocytes
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Gastric ulcer
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2. Chief cell, zymogenic cell
 Distribution:
numerous in the basal part
of the glands.
 Structures:
LM: Low columnar, A
round and basally-located
nucleus.
Basal cytoplasm is
basophilic and apical is
light-stained
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EM:
RER, Golgi apparatus
and apical granules
(pepsinogen).
 Functions:
secrete pepsinogen
Pepsin can break down
proteins into peptides and
solid food become liquefied.
Inactive
pepsinogen
HCl
Highly active
pepsin
digest proteins
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3. Mucous neck cell
Distribution: neck part of the
gland.
Structures: Columnar cells, A
flattened and basally-located
Nucleus
The cytoplasm is pale-stained in
HE stain.
Functions: mucus secretion.
4. undifferentiated cell : can
multiply to replace other cells and
play an important role in healing.
5. Endocrine cell:
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Cardiac glands and pyloric
glands
Distribution:
The mucosa of cardia
and pylorus respectively.
 Function:
Mucous secreting
glands.
 Structure:
The majority of cells is
mucous cells. Occasionally,
parietal cells, chief cells and
endocrine cells is present.
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③ muscularis mucosa:
2 sublayers of SM: inner circular and outer longitudinal
other layers of stomach
Muscularis is well developed
------three sublayers:
oblique, circular
and longitudinal
serosa
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Small intestines
Components:
Small intestine is a tube, 5 meters long.
It is composed of 3 parts:
Duodenum: 25 cm long
Jejunum: 2 meters long
Ileum: 3 meters long
Functions:
 The small intestine is the site of terminal food digestion,
nutrient absorption and endocrine secretion.
The nutrients are absorbed by the epithelial cells.
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General Structure:
The wall of the small intestine includes 4 layers:
 Serosa
similar to other segments
 Muscularis
 Submucosa:
 Mucosa exhibit several special features, will be described
below.
Mucosa
Lamina propria
Submucosa
Muscularis
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Mucosa
The surface area is 600-fold(200m2) increased.
Three special fetures as following:
1.Plicae circulares(3-fold) →2. Villi(10-fold)→3. Microvilli(20-fold)
Gross inspection
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1. Plicae circulares (Circular folds)

Structure : Mucosa and part of submucosa project into the
lumen, which is so large that be readily seen with naked eye.

Distribution: most develped in the jejunum.
Become fewer and less in the ileum.

Function: increase the surface area and slow down the
passage of the contents to facilitate absorption.
Gross inspection
Tissue section
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2.Intestinal Villi:

Structure: finger like projections, 0.5-1.5mm long ,consisting of a core of
connective tissue covered by a surface epithelium .
The CT core contains 3 important structures:
 Numerous fenestrated Cap., which allow rapid absorption of nutrients
into the blood.
 A central lymphatic Cap. called a central lacteal. Distal ends blindly and
proximal ends in a plexus of lymphatic V.
 Some smooth muscle cells
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intestinal villi under SEM
intestinal villi under LM
Distribution: most developed in the duodenum, decrease along SI.
Function : villi can increase the surface areas 10-fold.
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3. intestinal glands(Crypts):
 The invagination of epithelium into lamina propria.
 Really simple tubular glands.
 They are lined by epithelium continuous with that of the villi.
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The epithelium
Epithelial lining is simple columnar epi.
Epithelium of villi contains columnar cells, goblet cells,
endocrine cells .
Epithelium of Crypts are also lined by undifferentiated cells and
Paneth cells except for the above three .
Paneth cells
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1. Absorptive columnar cells

Function: digestion and absorption of nutrients
LM: tall columnar cells, an oval nucleus located in basal part.
Free surface have striated border .
EM: microvilli arranged in regular manner. Usual organelles, such as
lysosomes, smooth ER, and mitochondria.
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& Free
surface : microvilli.
Each microvillus is composed of a wall of cell membrane and central
cytoplasm with microfilaments. The microfilaments are continuous with
terminal web. Digestive and absorptive processes take place.
& Lateral sides: junctional complexes
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2. Goblet cells
Like a drinking glass, broad above and narrow stem attach to a base.
LM: It is pale by HE staining.
The nucleus is flattened or triangular and located near the
base of cells.
EM: An expanded upper part with mucin granules.
well developed Golgi complex and RER.
Function: secret mucous for lubrication.
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3. Paneth cell
Distribution: at the base of intestinal glands.
LM: Pyramidal and present in groups. And contains acidophilic granules
in the apical region.

EM: considerable RER, usual organelles, and large granules.
Function: produce lysozyme and defensin.
EM
LM
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4. Undifferentiated cells
LM: Columnar cells in the epithelium of the crypts. The structure
is similar to absorptive cells. In mitosis.
EM: Cytoplasm contains secretory granules.
Function: Proliferate by mitosis to form new cells and migrate
to reach the wall of villi.
5. Endocrine cells (described later)
It is difficult to identify with HE staining.
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
Duodenum
---Brunner’s glands=duodenal glands
Function:
produce alkaline
mucus to neutralize
gastric acid
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Ileum
 ---Peyer’s patches
aggregated
lymphoid nodules

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Distinguish features of small intestines

Villi are important characterization for identification of
small intestine,most well-developed in jejunum.

Duodenum has duodenal glands in the submucosa.

There is not hard and fast line of distribution between
jejunum and ileum.

Jejunum has fewer solitary lymphoid nodules and
greater vascularity.

Ileum has abundant aggregated lymphoid nodules.
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Large intestines

Mucosa: no villus and no circular
folds. Well-developed large intestinal
mucosa
glands, numerous goblet cells.

Submucosa: CT with fat cells.
submucosa

Muscularis: 2 sublayers SM.
Inner circular layer,
Outer longitudinal layer
muscularis
 Adventitia: Serosa, except posterior ascending and
descending colon.
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Mucosa
 structure: Lined by simple columnar epi. and the lamina propria is
filled with tubular . 4 types of cells.
 Columnar cells: absorb water and Ions, secrete mucus
 Goblet cells: secrete mucus.
 Endocrine cells (describe below)
 Stem cells: renew other cells.

Functions:
absorb water and ions
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Appendix
The structure of the appendix resembles that of the colon
with following differences.
1. The appendix is the narrowest
part of the gut and is a blindended tubule.
2. The crypts are poorly formed.
3. The mucosa and submucosa
contains abundant lymphoid
tissue.
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Gut-associated lymphoid tissue (GALT)
 Lymphoid nodules
• Solitary (jejunum) and aggregated (ileum) lymphoid nodules.
• Most prominent in ileum, forming Peyer’s patches.
 Immune cells
Eosinophil, Lymphocytes, Macrophages, Mast cells and Plasma cells
Function: protection
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M (microfolds)-cells: is specialized epithelial cells overlying Peyer’s
patches. M-cells can capture antigen and present it to immune cells.
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The endocrine cells of the guts

The epithelium contains scattered cells that have an
endocrine function (enteroendocrine).

The cells can be identified by the presence of granules
that is blackened with silver stain--- argentaffin cells
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some
biologically active substances (amines or polypeptides)
have been located in these cell, which can be found in nerve
system.

Gastro-entero-pancreatic endocrine system
The action affects neighboring cells (paracrine effect) and/or
cells at distant sites through the blood (endocrine).

Hormones
include:
glucagon, gastrin, secretin,
gastric inhibitory peptide,
cholecystokinin, somatostatin,
motilin, serotonin, substance P,
vasoactive intestinal peptide
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Quiz
Fig1
Fig2
Fig3
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Fig 4
Fig 5
Fig 6
Fig 7
Fig 8
Fig 9
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
Key points
General structure of the wall of digestive tract
The wall includes: mucosa, submucosa, muscularis and adventitia

Mucosa of stomach------epithelium, gastric gland: cell components
and function

3 types of features to greatly increase luminal surface of small
intestines : Plicae circulares、 villi 、 Microvilli----components
and function

Cell components of intestinal epithelial lining and small intestinal
gland

Esophageal gland and duodenal gland
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ASSIGNMENTS:
1. Describe four layers of the wall of digestive tracts.
2. Compare structural features and function of parietal
cells and chief cells.
3. Describe 3 types of features which greatly increase luminal surface
of small intestines .