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Stomach - Part 2 : The inner-layers of the Stomach

This follows the page introducing the stomach - with diagrams of the basic areas of the stomach and the outer-layers of the stomach.

Also recall the list of layers of the wall of the stomach.
This information is repeated here in the form of the diagram below:


(1) Layers of the Stomach Wall

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. In order to identify the different types of cells that line the stomach and the functions of each of these types of cells it is necessary to describe the inner-layers of the stomach (i.e. the layers of the mucosa).

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.

 

(2) The Mucosa (of the Stomach)

The cells identified in the diagram above are:

  • Surface Mucous Cells (or "Mucous Surface Cells") - which secrete mucus.
  • 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.

 

(3) 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.

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