Parietal Cells in Stomach在线视频

Hello everyone,

today we will talk about the digestive organ

--stomach.

Let's start with a case.

Rose is 29 years old.

She complained of pain in the upper belly

for the last two months.

Gastroscopic examination revealed an ulcer

in the lesser curvature of the stomach.

The doctor said the ulcer was caused

by the acidic gastric juice

that digested the tissue of stomach wall.

Rose wondered

where the acid in her stomach came from,

how was the wall of stomach protected normally,

and what condition might have caused her problem?

On completion of this session,

you should be able to identify

the basic structures

of stomach mucosa,

describe the morphology

and function of parietal cells

in gastric glands,

and explain some clinical correlates.

Stomach is the organ of temporarily

storing the masticated food bolus,

which enters the stomach from the oral cavity

through the esophagus.

The wall of stomach is made up of four main layers:

the mucosa, submucosa, muscularis, and serosa.

Stomach mucosa produces gastric juice that

contain proteases and hydrochloric acid.

Hydrochloric acid can kill or inhibit bacteria

and provide the acidic pH of 2

for the proteases to work.

The food boluses

are stored and converted into chyme,

partially digested food,

and finally to the small intestine

for additional digestion and absorption.

The production of gastric juice

is correlated to the function of

surface mucous cells

and the cells of gastric glands.

In this picture,

we can see the single layer of columnar epithelial

lining on the inner surface of the mucosa.

They also extend into the lamina propria

to form a gastric pit.

There are 1-4 tubular gastric glands

at the bottom of each pit.

So, products of surface mucous cells

and gastric glands

can be released

to the lumen through the gastric pits.

The simple columnar epithelium

produces a large amount of polysaccharide mucus

on the inner surface of the gastric lumen.

The mucus is synthesized in the cytoplasm

which is lightly stained

in the routinely prepared slides.

Because of the location and function of these

simple columnar cells,

we also call them surface mucous cells.

Beneath the gastric pit are gastric glands.

The glands distributed in the fundus

and body of the stomach are called fundic glands,

since the structures

in these two regions are similar.

There are 5 kinds of cells in the fundic glands:

parietal cells, chief cells, neck mucosal cells,

endocrine cells, and stem cells.

The cells with round or pyramidal morphology

and intensely eosinophilic cytoplasm

are parietal cells.

Parietal cells are mainly located

in the upper part of fundic gland,

secreting hydrochloric acid and intrinsic factor.

Under the electron microscope,

parietal cells

contain an extensive secretory network,

also called canaliculi.

Parietal cells

have an intensely eosinophilic hematoxylin

and eosin stain under light microscope.

A canaliculus

is a deep in-folding of the cytomembrane.

They are formed to increase the surface area

of the parietal cells for secretion.

The membrane of parietal cells is dynamic

when the cell is in different states.

In the resting state,

a number of tubulovesicular structures

can be identified in the apical region,

but there are few microvilli.

When activated to produce hydrochloric acid,

these vesicles fuse with the cell membrane

to form the canaliculi and microvilli,

thus providing an increase

in the surface of the cell membrane.

The large number of mitochondria

is responsible to produce ATP

for the active transport

of hydrogen and chloride ions.

These membrane structures

give the strong acidic appearance

of the parietal cells

in hematoxylin and eosin staining.

Hydrochloric acid

is released for protein digestion

and is also to keep the stomach immune

from infection.

The tissues of stomach wall also contain protein.

So, how can it manufacture acid and enzymes

without damaging its own tissue?

It is related to the mucus secreted

by the surface mucous cells.

Mucus is a mixture of water

and polysaccharide proteins

that causes it to become viscous and slippery.

The gastric mucosa produces so much mucus

that it insulates itself

from the contents and provides a barrier

to protect the stomach wall

from being digested by its own enzyme.

However, over-acidity in the stomach

will be beyond the protection of mucus,

and results in the acidic juice

eroding the tissue of the gastric mucosa,

forming an ulcer.

For a long time,

the hydrochloric acid was considered

the most important reason

for peptic ulcer.

While in 1982,

two Australian scientists, Warren and Marshall,

discovered and successfully cultured

the bacterium,

Helicobacter pylori,

from patients' stomach.

They found that the bacteria were correlated with

chronic gastritis(inflammation of the stomach)

and peptic ulcer.

H. pylori are spiral-shaped bacteria.

They are able to survive

in the strongly acid environment of the stomach.

Inside the mucus lining of the stomach,

the bacteria cannot be killed

by the immune system.

Their presence weakens the defensive barrier

and expose the stomach wall tissue

to digestive juices,

so leading to

inflammation and ulceration of the stomach.

In fact,

researchers believe that

H. pylori is responsible

for the vast majority of peptic ulcers,

about 80% of gastric ulcers

and 90% of duodenal ulcers.

Besides hydrochloric acid,

parietal cells also produce intrinsic factor.

Intrinsic factor is required for the absorption

of dietary vitamin B12 in the small intestine.

Vitamin B12

is needed for the development of red blood cells.

Long-term deficiency in vitamin B12 can lead to

pernicious anemia,

characterized by large fragile erythrocytes.

Atrophic gastritis is a process of

chronic inflammation of the stomach mucosa,

leading to loss of gastric glandular cells

and their eventual replacement

by the intestinal and fibrous tissues.

Therefore, atrophic gastritis,

particularly in the elderly,

is often associated with

the inability to produce intrinsic factor.

Decreased vitamin B12 absorption

leads to reduced red blood cells and anemia.

Parietal cell is just one of the cells

in the gastric glands.

We also have chief cells, neck mucosa cells,

endocrine cells, and stem cells.

Today we have mainly talked about

the structure of stomach mucosa,

the morphology and function of parietal cells.

The two most important functions are productions

of hydrochloric acid and intrinsic factor.

Here are the references.

Thank you for your attention!