The layers of the
stomach shown in the diagram on the left are (from
the centre of the stomach outwards):
Lumen
of the Stomach
* Mucosa - has three layers and also
contains the gastric pits (openings of passageways
that extend towards the inner stomach wall)
Mucosal Layer - Mucosal epithelium
Mucosal Layer - Lamina propria
Muscosal Layer - Muscularis mucosa
* Submucosa
* Muscularis externa - three layers
of muscle tissue, whose fibres are orientated in different
directions
Muscle Layer - Oblique
Muscle Layer - Circular
Muscle Layer - Longitudinal
* Serosa
Recall the arrangement
of the outer (muscle) layers:
Above: Diagram of the Stomach Wall.
The epithelial cells that line the stomach form the
mucosal epithelium
layer.
When the stomach is empty the mucosa lies in large folds
called rugae
and which look like wrinkles. The rugae flatten as the
stomach fills.
It is necessary to describe the inner-layers of the
stomach (i.e. the layers of the mucosa) in further detail
in order to identify the different types of cells that
line the stomach and the functions of each of these
types of cells.
The surface of the mucosa is a layer of nonciliated
simple columnar epithelial cells called surface
mucous cells.
There are also many columns of secretory
cells called gastric glands
that line narrow channels called gastric
pits.
That is, epithelial cells not only line the inside surface
of the stomach, but also form many narrow passages
called gastric pits
that lead from the lumen of the stomach outwards towards
the inner stomach wall, or submucosa.
Neck Mucous Cells
(or "Mucous Neck Cells")
- which secrete a mucus whose acidity is more neutral
than that secreted by the cells at the surface of
the stomach lining.
Chief Cells
Parietal Cells,
and
G Cells
Gastric Glands lining the Gastric Pits:
There are three special types of exocrine glands (neck
mucous cells, chief
cells and parietal
cells) that secrete chemicals into the
stomach. There is also one type of hormone-producing
cell in the lining of the gastric pits, which is called
a G cell.
Secretions from cells located in the Stomach
Type of Cell
Secretion
Notes
Surface Mucous
Cells
(or "Mucous Surface Cells")
- secrete a mucus
Neck Mucous
Cells
(or "Mucous Neck Cells")
- secrete a mucus
whose acidity is more neutral than that secreted
by the cells at the surface of the stomach lining.
The mucus secreted
by the muscous neck
cells has a more neutral pH than
that secreted by the cells at the surface of the
stomach lining.
Chief Cells
- secrete pepsinogen
Pepsinogen is an
inactive gastric enzyme
which is converted to pepsin,
a protein-digesting
enzyme.
Parietal Cells
- secrete hydrochloric acid,
and an intrinsic factor
(involved in the absorption of vitamin B12).
Hydrochloric acid
assists in the conversion of pepsinogen to pepsin
(mentioned above).
Insufficient intrinsic factor
can lead to pernicious anemia because vitamin
B12 is necessary for the production
of red blood cells (called erythrocytes).
Gastric
Juice:
The secretions of the surface mucous cells, neck
mucous cells, chief cells, and parietal cells
are known collectively as gastric
juice.
(Hence gastric juice
includes mucous, pepsinogen,
hydrochloric acid and intrinsic factor.)
G Cells
- produce and secrete the hormone gastrin.
Gastrin :
stimulates secretion of gastric juice,
increases the contractions of the gastro-intestinal
(GI) tract, and
relaxes the pyloric sphincter.
The next pages in this series are about
the anatomy of the liver (accessory
organ)
and the anatomy of the small
intestines - which is the next stage of the alimentary
tract.
... End of Page ...
See related pages listed top-left or visit the Human
Body Index.
