Introduction

Gastrointestinal hormones are chemical messengers that regulate intestinal and pancreatic functions such as absorption, digestion, etc. The following is a detailed discussion of what gastrointestinal hormone is and how it works or its function.

All hormones are small chemical messengers produced and released by one cell or group of cells and control or influence target cells. Target cells are cells where the chemical signals act. Hormones work by binding to receptors on or within the cell and changing the activity of that particular cell. They are biochemical fluids that are secreted from cells or glands in a specific part of the body.

Mainly communicate between organs and cells in the body. The various physiological processes and behavioral functions of the human body such as sleep, physical growth, reproduction respiration, etc. are regulated by hormones. There are different types of hormones. The gastrointestinal hormone is one of them (1) & (5).

Gastrointestinal hormone

A gastrointestinal hormone is a type of hormone secreted from the gastrointestinal tract such as the stomach, pancreas, and intestine. They help the digestion of food and the secretion of digestive juice. The endocrine glands are ductless glands. They pour their secretion into the surrounding blood for transport to the site of action or distantly located target organ. Their secretions are called hormones (2).

The endocrine glands are two types in humans. These are pure endocrine glands and partial endocrine glands. The partial endocrine glands contain various types of glands or tracts. The gastrointestinal tract is one of them. This is where the gastrointestinal hormones are released (3).

Interesting facts about Gastrointestinal hormone

Gastrointestinal hormones are peptide hormones.
It consists of a single polypeptide chain.
The molecular weight of these types of hormones is very low.
They are water-soluble.
This hormone is responsible for maintaining the normal, rhythmic peristaltic activity of the intestine.
These hormones are a different group of peptides that are released into the bloodstream in response to certain stimuli.
They activate the signal transduction pathway.
It plays a role in regulating intestinal function to aid digestion.
The peptide chain of this hormone is usually made up of less than 50 amino acids.
These hormones have some properties, such as multiple active isoforms, signals through multiple intracellular pathways, multiple membrane-bound receptors, etc (2) & (4).

Example

Gastrin is a type of gastrointestinal hormone. They are secreted from epithelial cells of the GI tract, transport through blood, and induce the secretion of HCL from the stomach wall (2).

Types of gastrointestinal hormones

There are various types of gastrointestinal hormones. These hormones are classified based on their chemical structure. The gastrointestinal hormones are as follows

1. Gastrin

Gastrin is a type of peptide hormone.
It is secreted from the G cells of the pyloric antrum and pancreas of the stomach.
These types of gastrointestinal hormones stimulate and maintain the expansion of the gastric epithelium.
It stimulates the secretion of histamine in enterochromaffin cells. This stimulation is only possible when gastrin binds to cholecystokinin B receptors.
They are secreted into the bloodstream.
These hormones are secreted in response to some stimuli, such as stomach antrum distension, hypercalcemia, vagal stimulation, etc.
When food enters the stomach, gastrin is secreted into the bloodstream and carries gastric cells to the stomach wall through the circulatory system (1) & (4).

2. Cholecystokinin

It is a gastrointestinal peptide hormone that is present in the gut.
This hormone is also considered a neurotransmitter secreted by the nervous system, especially in the hypothalamus.
Cholecystokinin secretion or production depends on factors such as the presence of certain nutrients from food in the gut, mainly fats and proteins.
It forms one of the major hormones hidden in the gastrointestinal tract together with gastrin and secretin.
Cholecystokinin is mainly secreted from the upper small intestine.
It is also known as pancreozymin.
These types of hormones are generated from a single polypeptide chain that encodes a 115-amino acid.
The strongest stimulus for the release of this hormone is the presence of partially digested fats and proteins in the lumen of the duodenum.

3. Secretin

Secretin is a peptide hormone produced in the S cells of the duodenum, which is located in the intestinal glands.
It is encoded by the SCT gene in the human body.
They are synthesized as a 120 amino acid precursor protein known as prosecretin.
It has a molecular weight of 3055.
Secretin was the first identified hormone.
It is a type of gastrointestinal hormone that regulates water homeostasis throughout the body.
They are soluble in water.
It is released by the digestion of proteins and fats.

4. Glucagon

Glucagon hormones are bound to a G protein-coupled receptor located in the plasma membrane of the cell.
It is responsible for maintaining blood glucose levels.
These types of hormones are secreted from the stomach and small intestine.
They stimulate the breakdown of glycogen.
It mostly affects the liver cells.
This type of hormone is activated when glucose levels are low in the blood.
It is produced by the alpha cells of the pancreas.
Glucagon is a polypeptide chain with 29 amino acids.
Its molecular mass is 3485 Da.

5. Vasoactive intestinal peptide

The vasoactive intestinal peptide is a peptide hormone with a residue of 28 amino acids.
It belongs to the glucagon/secretin superfamily.
In humans, these hormones are encoded by the VIP gene.
It is secreted from the entire small intestine and colon.
These hormones are found in the brain, blood, pancreas, and autonomic nerves.
Like other gastrointestinal hormones, the vasoactive intestinal peptide is synthesized as a molecule that contains a single peptide.
It is a neuropeptide.
These types of hormones are distributed in the central and peripheral nervous systems.

6. Gastric inhibitory peptide

Gastric inhibitory peptide hormones are present in glucose and fat in the small intestine.
It belongs to the secretin family.
This hormone was first discovered as an ingredient in the intestinal extract.
Basically, it is known as enterogastrone.
It is also known as a glucose-dependent insulinotropic polypeptide.
This type of hormone interferes with gastric motility and acid secretion.
Gastric inhibitory peptide hormones are secreted from the K cells of the duodenum and jejunum.
The molecular weight of GIP is 359.7 Da. It is encoded by the GIP gene in the human body.
They are secreted from the mucosal epithelial cells of the small intestine.
It is one of the barrier hormones.

7. Motilin

It is a 22-amino acid polypeptide hormone.
Motilins are encoded by the MLN gene in the human body.
They belong to the motilin family.
The hormone was first discovered by J. C. Brown.
These hormones are also found in the gastrointestinal tract of pigs, cows, and rats and in the central nervous system of rabbits.
They are secreted from the M cells of the duodenum and jejunum.
It stimulates the endogenous release of the endocrine pancreas.
The molecular weight of motilin is 2698 Daltons.
It has two basic forms. Both are formed by 22 amino acids. There is an additional C-terminal edge in the second form of
The secretion of this hormone is stimulated by an alkaline pH located in the duodenum.

8. Somatostatin

Somatostatin is a peptide hormone that controls the endocrine system.
It is secreted by delta cells in different parts of the digestive tract, such as the pyloric antrum, duodenum, and pancreas.
They are encoded by the SST gene in humans.
Somatostatin is also an inhibitor hormone.
Its molecular weight is 1637.9 Dalton.
These types of hormones are the inhibitors of pituitary growth hormone secretion.
It is soluble in water.
There are two basic forms of somatostatin hormone. The first form consists of 14 amino acids and the second form is made of 8 amino acids.

9. Ghrelin

Ghrelin is produced in the gastrointestinal tract, basically the stomach.
It is also known as the hunger hormone or lenomorelin.
These hormones are secreted when the stomach is empty.
It is a 28-amino acid peptide hormone.
Ghrelin levels increase before meals and decrease after meals.
Its molecular mass is 3370.9 Dalton and the molecular formula of ghrelin is C₁₄₉H₂₄₉N₄₇O₄₂.
These hormones exist in two main forms, n-octanoyl- modified ghrelin and des-ocyl ghrelin.
Ghrelin hormone is sometimes produced in the brain, lungs, adrenal cortex, and kidney (4) & (5).

Function or uses

1. The main function of the gastrin hormone is to stimulate the secretion of gastric acid (HCL) from the parietal cells of the stomach and increase the motility of the stomach.

2. Cholecystokinin stimulates the secretion of pancreatic enzymes constricts the gallbladder and facilitates the secretion of bile in the duodenum. It acts as a neurotransmitter or neuromodulator.

3. Secretin helps to control the pH of the duodenum, inhibits gastric acid secretion from parietal cells of the stomach, and stimulates bicarbonate production from pancreatic duct cells.

4. Glucagon increases the amount of sugar or glucose in the blood. It stimulates the breakdown of amino acids, increases blood flow to the kidneys, and improves liver function by repairing cells.

5. Vasoactive intestinal peptide hormone helps to control the secretion of gastric acid and water. It also regulates blood flow in the gastrointestinal tract and smooth muscle activity.

6. Gastric inhibitory peptide hormone’s main functions are to inhibit gastric secretion, and motility and stimulate insulin secretion.

7. The primary function of the motilin hormone is to regulate the movement of the gastrointestinal tract by controlling the migration motor complex.

8. Somatostatin inhibits the production of other hormones and stops the unnatural rapid reproduction of cells. This hormone regulates the secretion of hormones from the pituitary gland. They also act as neurotransmitters.

9. Ghrelin hormone sends a signal to the brain to feel hunger. It plays a key role in controlling calorie intake and body fat levels. The main function of ghrelin is to increase appetite (1) & (4).

Q&A

1. What are the gastrointestinal hormones?

Gastrointestinal hormones are a type of peptide hormone secreted from endocrine cells, like the gastrointestinal tract. It is a chemical messenger. Their primary function is to control the intestinal, and pancreas.

2. Which of the following gastrointestinal hormones is not secreted by the small intestine?

Gastrin is not secreted by the small intestine.

3. What cells are responsible for producing gastrointestinal hormones?

Endocrine cells are responsible for producing gastrointestinal hormones.

4. Why does fat worsen the symptoms of gerd gastrointestinal hormones?

The increased risk of gerd is thought to be due to the creation of excess abdominal fat on the abdomen that causes hormonal changes to increase estrogen exposure which can lead to obesity in infected individuals. Excess fat around the abdomen compresses the stomach, so more fluid flows up the esophagus. This increases the chances of feeling stomach acid leakage and gerd.

5. What hormones are produced in the gastrointestinal tract?

Gastrin, somatostatin, ghrelin, secretin, cholecystokinin, glucagon, motilin, etc. are produced in the gastrointestinal tract.

References

1. B. Powar and G. R. Chatwal. Biochemistry, B. SC (general & honors course) and M. Sc. Himalaya publishing house, Chapter: Hormones. Page no: 322 to 341.

2. Ajoy Paul. Zoology Honours, Volume- 1, Books & Allied (P) Ltd. Chapter: Endocrine system. Page no- 697 to 723.

3. Hema Batra and Shikha Sharma. All in one, Biology, CBSE Class XI. Arihant Prakashan. Chapter: Chemical coordination and integration. Page No: 544 to 564.