Gastric Gland – Anatomy, Types, Functions, Importance
Gastric Glands are situated at the linings of the stomach. The stomach is the first organ that plays a vital role in the digestive system of humans. The stomach is a connector between the Esophagus & Duodenum. Duodenum is the beginning part of the small intestine. Basically, the Stomach can be divided into four parts. They are Cardiac Region, Fundic Region, the Stomach Body, and Pyloric Region. Gastric Glands are situated in all three parts. As it is present in the wall of the Stomach then it is obvious, that they are present throughout the stomach. Gastric glands help to digest the food which human consumes. Gastric glands secrete gastric juice which is the main component of the digestive system. It breaks down the protein available in the food. In this way, the simpler form of food will be easily digestible by the small intestine.
Location of Gastric Gland
The stomach wall can be further divided into four parts. The outermost part is Serosa. Then Muscularis, Submucosa & the inner most is Mucosa. Among them, Serosa is the protective layer of the stomach. Muscularis is the muscular part of the stomach wall. It is completely made with smooth muscle cells. Submucosa & Mucosa are two important parts. From there all the secretion comes to the body of the stomach. Gastric glands are situated in the Mucosa layer of the stomach wall. Gastric glands are placed there in a form that they create a pit. These are called Gastric Pit. From the Gastric glands, the Gastric juice secretes & comes into the lumen of the stomach.
Structure of Gastric Gland
Basically, Gastric glands are made of different types of cells. These cells are responsible for the secretion of gastric juice & many other types of digestive juice. These cells are:
These cells are made with two subcells. They are Surface Mucous Cells & Mucous Neck Cells. These cells are situated at the beginning part of the gastric glands. These cells are responsible for the mucous secretion in the stomach. They help to protect the stomach from gastric acid. As they build a protective layer in the stomach, gastric acid can’t able to react with the stomach itself.
Parietal Cells/Oxyntic Cells
These cells are present in the Gastric glands at random locations. After the part of the Foveolar cell, they can present at any random part of gastric glands. Among all the cells, Parietal cells present a huge number. It is the most important of all the cells. As it needs to be always ready to secrete the HCl. Their main function of them is to secrete the HCl. In these cells, there are fine channels called Canaliculi which help to secrete the HCl. With the help of Canaliculi, HCl directly comes into the stomach body. Along with HCl, Castle’s Intrinsic Factor is also secreted from Oxyntic cells.
Chief Cells/Zymogenic Cells/Peptic Cells
These cells are situated above Endocrine cells. These cells mainly secrete Pepsinogen in the stomach. During childhood, along with Pepsinogen, Prorenin enzymes are also secret from the Chief cells. But in adulthood, it stops secreting the Prorenin. Along with all these enzymes, from chief cells, a small amount of Gastric Lipase is also secreted. This gastric lipase helps to digest the fat in the food. But it is in a very small amount that we can ignore the presence of lipase in the gastric juice.
These cells are situated at the linear-like part of gastric glands. These Endocrine Glands can further divide into three major cells:
- G-Cells: These cells can find in the Pyloric region of the stomach. From these cells Gastric hormone secrets. This hormone regulates the secretion of gastric juice. Whenever there is a need G-Cells can stimulate gastric juice secretion.
- D-Cells: These cells do the opposite of the G-Cells. It suppresses the secretion of gastric juice. It secretes Somatostatin which helps to reduce gastric juice secretion.
- Enterochromaffin Cells (ECL Cells): ECL store & release Histamine & Serotonin. When the pH of the stomach becomes high ECL starts to secrete the Histamine. Now secretion of Histamine is determined by the Gastric hormone. The moreover target, in this case, is to secrete the gastric juice. But when the pH decreases, means the stomach is becoming acidic Histamine secretion stops & Serotonin secretes. This means there is no need for gastric juice in the stomach at that time. So, it stops the secretion of gastric juice.
Types of Gastric Glands
There are no such prominent types present in gastric glands. But some scientists divide them into different types as per their location. The stomach can divide into four parts, but the Gastric glands can divide into three types:
- Cardiac Gastric Gland-These gastric glands are present at the beginning of the stomach. The area is known as Cardiac Region. It is the region where Esophagus is connecting with the stomach.
- True Gastric Gland-These gastric glands are present in the middle of the stomach. These gastric glands are situated in the Fundic Region & Stomach Body.
- Pyloric Gastric Glands -These gastric glands are situated at the end of the stomach. The region is known as the Pyloric stomach. It is the portion where the Duodenum is connected with the Stomach.
Importance of Gastric Glands
Gastric glands are the main pillar of the digestion system. When human consumes food, it directly comes to the stomach. Though before that they come across some enzymes in salivary glands. Though they are not enough to completely digest the food. Some amount of carbohydrates breaks down there. But when the food comes into the stomach, it starts to break down by the gastric juice. Gastric juice is nothing but Hydro Chloric Acid (HCl). This strong acid completely breaks down (50%-55%) the food. After breaking down the food it converts to Chyme. Chyme is a pulp-like structure that is made with partially digestive food & gastric juice. This pulp is now easily digestible by the intestine. The alkaline nature of the intestine will reduce the acidic nature of the Chyme. Now, if there is no Gastric Gland present in the stomach then digestion will be difficult. As the food which human consumes will directly come to the intestine. And intestine does not have to capacity to break down the complete food. Hence, balance in the digestion system will lose.
Mechanism of Gastric Juice Secretion
The main component of gastric juice is HCl. HCl is secreted from the Parietal cell. Now all the procedures will take place inside the Parietal cell & its lumen of it.
- At first, the water in the Parietal Cell will get dissociation and will produce Hydrogen ions & Hydroxyl ions.
H2O ——-> H+ + OH–
- Now, the Hydroxyl ions will combine with Carbon Dioxide. Carbon Dioxide is present in the blood vessels. After combining, this will produce Bicarbonate ions.
CO2 + OH– ——-> HCO3–
- Now, Chloride ions are present outside of the Parietal cells. At this moment the Bicarbonate ions will through outside of the Parietal cell. And in exchange Chloride ions will come inside the lumen of the Parietal cell. In this way, the ion balance will be the same in the lumen.
- Not only the Chloride ion but also along with that Potassium ion will come inside the lumen. All this exchange will be done through the Canaliculi of the Parietal cell.
- Now, the scenario is that inside the cell there is a Hydrogen ion. And outside of the cell, in the lumen, there is a Chloride ion. In the membrane of the Parietal cells, there are “Protein Pump”. The function of the “Protein Pump” is to exchange the positive ions. Now, in this case, the Potassium ion will come into the cells & in exchange for that Hydrogen ions removes inside the lumen.
- Now, in the lumen, a Hydrogen ion is present, as well as a Chloride ion is also present. Both combine with each other & produce Hydro Choric Acid. This is stored in the Parietal cell & when there is a need it will come to the body of the stomach with the help of Canaliculi.
H+ + Cl– ——-> HCl
Uses/Functions of Gastric Glands
Gastric glands not only secrete gastric juice (HCl) but also, secrete many other factors which play a vital role in digestion
Function of HCl
From Peptic cells of Gastric glands, pepsinogen is secreted. This pepsinogen is activated by the HCl. Also, HCl helps to absorb the iron & vitamins which are present in the food. Mainly, vitamin B12 is absorbed by gastric juice. As this vitamin may cause allergic symptoms in the human body. Also, Strong acid like HCl helps to kill the bacteria which may be present in the food which human consumes. Hence, it helps to protect the body’s immunity.
Function of Pepsinogen
With the help of HCl Pepsinogen converts to Pepsin. Pepsinogen is the inactive form of Pepsin. Pepsin helps to digest the protein which is present in the food. After completely breaking down the protein the food modifies to Chyme.
Function of Mucus
Mucus secretes from the Gastric Glands. This mucus is the protecting layer of the stomach. Pepsin is responsible for the digestion of protein. Now, stomach layers are made with protein. So if the Pepsin comes to contact with the wall of the stomach, it will start destroying the layer of the stomach. Hence, the stomach will be harmed. This is why Mucus is present in between the Gastric juice & the stomach wall.
Function of Endocrine Cells
From the endocrine cells of the gastric glands, Gastrin & Histamine secretes. They help to regulate the secretion of gastric juice.
Disorder of Gastric Glands
Though it is very rare to find a gastric gland disorder, still we can list two major disorders of gastric glands.
- Fundic gland polyposis is a disease where some polyps may develop in the body of the stomach due to the non-function of gastric glands
- Pernicious anemia is another disease where the absorption of Vitamin B12 decreases due to the inactivity of gastric glands.
- Also if the Mucus secretion stops, then the inner inflammation of the stomach may be visualized. Also, this can lead to ulcers.
Question 1: How many phases are there in gastric secretions? Name the phases.
There are three phases. They are Cephalic, Gastric & Intestinal. All of these phases are circulated by the human phycology. It depends upon the thought process of humans for a particular food.
Question 2: At which time of the day gastric juice secretion is at its top level?
There is not any evidence, but scientists believe that the secretion of gastric juice is at its top peak when it is dark night. Mainly when midnight comes. At that time the human body takes a rest, after getting their food, that is the best time to digest whatever human consumes.
Question 3: At which condition does the gastric juice secrete high in amount?
Scientists believe that during fasting gastric juice secretes most. At the time of fasting, gastric juice secretion increased with time. Histamine regulates the secretion of gastric acid at the time of fasting or fasting situations.
Question 4: What happens when the stomach secretes more gastric acid than the normal quantity?
Due to some disorders with gastric glands, it is quite rare to visualize gastric glands secreting more gastric juice. This disease is known as gastric hyperacidity. Often it is called acid dyspepsia disease.
Question 5: What can help to reduce the gastric acid secretion in the stomach?
Scientists believe that incurring water in large amounts can control gastric acid secretion. It is like an external factor that can control the secretion of gastric juice. As water will mix up with HCl & reduce the secretion.