2010 GI 2 complete +lab (2) - GASTROINTESTINAL SYSTEM(GI...

GASTROINTESTINAL SYSTEM (GI Tract).
I. General Organization, Esophagus and Stomach.
Barry R. J. Rittman, Ph.D .
Reading: Gartner and Hiatt Chapter 14, p277; Sheedlo, Chapter 14, p134-138
Learning Objectives:
• Understand the organization of the four layers of the Gastrointestinal tract.
• Describe the 4 layers of the esophagus, with emphasis on the epithelium and the location of the
gland types in the underlying layers.
• Describe unique features of the tunica muscularis of the esophagus and stomach.
• List histologic characteristics common to glands throughout the stomach.
• Name gland types in the different zones of the stomach.
• List their differences based on pit and gland length. gland shape, cell types, and function.
• List cell types, found in gastric glands, and know the functions of each.
Key Words: Tunica mucosa, lamina propria, submucosa, muscularis, adventitia, serosa, Meissner’s
plexus, Auerbach’s plexus, esophageal and mucosal glands, parietal cells and chief cells.
I. General organization
The gastrointestinal tract (=digestive tract), consists of a tube and associated glands and organs
that have arisen from the epithelium of the primitive gut.
The following notes refer only to the esophagus, stomach, small intestine, large intestine,
appendix and anal canal.
The 4 basic layers are shown above
1
Tunica Mucosa
Tunica Submucosa
Tunica Muscularis
Tunica Adventitia or
T. serosa

FOUR LAYERS
Tunica Mucosa
Tunica Submucosa.
Tunica Muscularis.
Tunica Adventitia or Tunica Serosa.
It will be easier to study the specific regions if you remember that the basic composition of
the each of the four layers is a reflection of the specialized function of each region.
A. Tunica Mucosa.
Composed of epithelium with basement membrane, lamina propria and muscularis mucosa.
1. Epithelium and basement membrane. The type of epithelium varies according to the
local functions.
Esophagus is flexible – to accommodate fluids and solid food while protecting the underlying
tissue from both temperature and abrasion from food.
The stomach must be protected from its own acid.
The intestines must have a high absorptive capacity.
In many regions the epithelium gives rise to ducts and glands that reside deeper in the wall of the
GI tract.
2. Lamina propria. A loose connective tissue sometimes with large numbers of cells of
the immunologic defense system; Rich vascular supply; Lymphatic vessels and glands may also
be present.
3. Muscularis mucosa. This is a very thin layer of smooth muscle usually close to the
mucosa. It has an inner circular and outer longitudinal layer but these are usually difficult to
delineate.
B. Tunica Submucosa.
This layer is under the mucosa and is loose connective tissue much less cellular than the mucosa.
This layer contains larger blood vessels and lymphatics, often glands and an important network
of nerves and ganglia belonging to Meissner's plexus .