DIG

ES

TIV

E S

YS

TE

M

By Chunmin LIANG & James Williams

What will happen if a little bean

is swallowed by you?

Please write a story by yourself.

I will provide you a chance for presentation

if it is convincing enough.

A little bean

Team work

General Function Of Digestive Tract

• Ingestion

• Mastication

• Motility

• Secretion

• Hormone release

• Chemical digestion

(from macromolecules to smaller molecules)

• Absorption (into blood and lymph)

• Elimination

General structure :

1. Mucosa

2. Submucosa

3. Muscularis

4. Serosa

The mucosa comprises:

Epithelium

Muscularis mucosae: a thin layer of smooth muscle seperating

mucosa from submucosa

Lamina propria: loose CT rich in blood vessels,

lymphatics, lymphocytes, smooth

muscle cells and often small glands

The submucosa contains :

Connective tissue layer with

①larger blood and lymph vessels

②submucosal plexus(nerves)

③sometimes glands

④lymphoid tissues

Mucosal Immune System，MIS

（mucosal-associated lymphoid

tissue，MALT）:

lymphoid tissues distributed in the

mucosa of digestive tract ,

respiratory tract、et al.

The first barrier against microbial invaders

50% of lymphoid tissues located in MALT

Pre-

plasma cell Lymph

nodes

Thoracic

duct Blood

Circulate back

to gut mucosa Plasma cell

Recirculation of lymphocytes

Lymphoid

nodules IgA

SP(secretory piece)

sIgA

Key point: How to understand the immune response in digestive tract?

antigen

M cell

lymphocyte

macrophage

Pre-

plasma cell Memory

B cell

Pre-

plasma cell

The Muscularis :

Smooth muscle,

consists of two layers

①Inner circular

②External longitudinal

The Serosa:

① can be “true serosa” (with a covering of

mesothelium)

② or “fibrosa” (without mesothelium)

Congenital megocolon

Tongue

Mucosa：

There are mainly 4 types of papillae

① Filiform papillae

② Fungiform papillae

③ Vallate papillae

④ Foliate papillae

Skeletal muscle

Cross each other in 3 planes

Providing the flexibility for speech,

positioning food,chewing and swallowing.

The comparation of 4 different papilla

Types Quantity Structural characteristics

Filiform

Most

numerous Sharp，partly keratinized，

lacking taste buds

Fungiform

Less Resemble mushroom,

has taste buds on its expanded

upper surface

Vallate

Least

numerous Largest，near the V-shaped

groove, have more numerous

taste buds (≥1/2 )

Foliate

papillae

Less poorly developed，

on the sides of tongue

Taste bud • Ovoid structure

• Each containing 50-75 cells

• Located in stratified epithelium of

the tongue and oral mucosa

The structure and function of taste bud

Salty

Sour

Sweet

Bitter (Half,elongated)

(Slender)

(Stem cells) Stem cells divide and

give rise to the other

two types

(apical)

(sensory axon form synapse with taste cell)

molecules (tastants) dissolved in saliva

Esophagus

Epithelium is stratified

squamous, non-keratinized

Submucosa has glands

(mucous)

Muscularis mucosae made of longitudinal bundles of smooth muscle

Serosa has mesothelium only within abdominal cavity

Muscularis externa can have skeletal and/or smooth muscle

Upper 1/3: skeletal muscle

Middle 1/3: mixed

Lower 1/3: smooth muscle

Mucosa and submucosa swell into the lumen to form

longitudinal ruga.

Stratified squamous, non-keratinized epithelium

Submucosa has glands (mucous)

Muscularis externa have skeletal

and/or smooth muscle

Traveling from esophagus to stomach,

the little bean finds that...the epithelium has changed!

Super!

Abrupt transition from stratified squamous epithelium to

simple columnar epithelium

The structures of Stomach

Gastric glands

mucosa submucosa muscularis serosa

Surface of mucosa covered with

simple columnar epithelium

Submucosal nerve plexus

Myenteric nerve plexus

Stomach • Is a mixed exocrine-endocrine organ

• Digests food

☆ continue the digestion of carbohydrates

☆ add acidic fluid to the ingested food

☆ transform food into a viscous mass

(chyme) by muscular activity

☆ promote the initial digestion of proteins by pepsin

• Secretes hormones

Famous HCl: hydrochloric acid

Pylorus Fundus/Body Cardia

Stomach ①

②

③

④

There are 4 regions with

different gastric glands...

(Deep pits and short glands)

Lamina

propria

Fundic glands

Muscularis mucosa

HCl and pepsin are mainly secreted in the

body and fundus regions

Cells in fundic gland

1.Surface mucous cells secret neutral mucus against

acidic gastric fluid

2.Mucous neck cells secret acidic mucus in the

top area of the gland

3.Parietal cells secret HCl and intrinsic

factor mainly in the upper

part of the gland

4.Chief cells secret pepsinogen in the

base of the gland

5.Enteroendocrine cells 6.Undifferentiated cells (stem cells)

?

...equiped with mitochondria and tubulovesicles

Intracellular secretory canaliculus

Parietal cell

Active

Under the observation of electron microscope

Rich in mitochondria

hydrochloric acid

FIGURE 15-19

The main steps in the synthesis of HCl

by parietal cell

Carbonic anhydrase

CO2 H2O + H2CO3 H+ + HCO3-

Intracellular canaliculus

Cl-

exchange

H+

Energy-dependent

+

HCl

( Hydrochloric acid )

pepsinogen pepsin

Chief cell

also named as zymogenic cell

Predominant in the lower

region of glands

Home work The comparation of 3 different cells

Types

Distribution L.M.

E.M.

Function

Parietal

cell

Chief cell

Neck

mucous

cell

?

( please send your answers to me by e-mail )

Inner layer

circular

Outer layer

longitudinal

Small Intestine: includes the duodenum, jejunum and ileum.

Mucosa

Submucosa

Muscularis

(2 layers)

Serosa

Villi

Central lacteal

Blood vessels

Intestinal gland

FIGURE 15-28

Observed by scanning electron microscope

Villi and Intestinal glands

Villus Absorptive cell

Striated border = microvilli = increase the absorptive surface area 20-fold

L.M. E.M. Function

Absorptive cell

central lacteal

Filled with

chylomicron

Demonstrated by your microscope, you will find…

Transport absorbed lipid into circulatory system…

Goblet cell

Acidic mucus

• Lie between the absorptive cells

• Increasing in number from duodenum to ileum

• Secrete acidic mucus for protection

from A. pancreatic enzymes

B. impeding bacterial invasion

Paneth cell

• Only found in intestinal glands

• Lies in the base of gland

• L.M. ---Acidophilic granules

• E.M.---RER, Golgi complexes

• Play antibacterial effects

Undifferentiated cell

Acidophilic secretory granules

contain lysozyme and defensin

Fight against

bacterial invasion

intestinal gland

The comparation

of 3 segments

Could you distinguish them,

Which is which?

duodenum, jejunum and ileum.

Key point: Which structures of small intestine are related with the

increased surface for enhancing absorption ？

Length:

Plica circulares: composed of mucosa and submucosa

Villi:

Apical microvilli:（striated border）

20-fold

10-fold

3-fold

Composed of epithelium and lamina propria

12 to 24 feet

So, as to my little bean, it is absolutely a long trip...

Large intestine (colon)

• no villi

• abundant goblet cells

• abundant large deep intestinal glands(crypts)

• absorptive cells have irregular short microvilli

• more lymphoid tissues in the lamina propria

Appendix

• narrow fingerlike

• at the inferior of cecum

• smaller and irregular lumen

• fewer and shorter crypts

• has no tenia coli

• masses of lymphatic tissue

in mucosa and submucosa

appendicitis If our little bean hides here,

what will happen?

The border of rectum and anal canal

Look!

The little bean was happy because he believed he arrived a new place…

Hey!! I still

alive!!