Hormones of Gastrointestinal Tract - A Discussion

Creator: Dr. Asna Fatma
Published: 2023-05-17T18:48:31

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The gastrointestinal tract secretes several hormones through its organs that aid in the digestion and absorption of food. Read further to know more.

Written by

Dr. Asna Fatma

Medically reviewed by

Dr. Ghulam Fareed

May 17, 2023

October 26, 2023

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Contents

What Are Hormones?
What Is the Gastrointestinal Tract?
What Are the Hormones of Gastrointestinal Tract?
What Is Gastrin and Its Functions?
What Is Cholecystokinin and Its Functions?
What Is Secretin and Its Functions?
What Is Ghrelin and Its Functions?
What Is Motilin and Its Functions?
What Is Gastric-Inhibitory Peptide and Its Functions?

Introduction:

Gastrointestinal hormones are a group of hormones responsible for helping digestion, absorption of food, and other functions of the gastrointestinal tract. Several digestive organs synthesize and secrete various gastrointestinal hormones like gastrin, secretin, ghrelin, motilin, etc. These hormones work on specific receptors and organs and carry out different functions. Therefore, any imbalance in these hormones can result in the development of various medical conditions.

What Are Hormones?

Hormones are signaling chemicals carried to distant cells and organs through complex biological processes to control physiology and behavior in multicellular organisms. These hormones operate as chemical messengers in the body, carrying messages from one region of the body to another through the bloodstream, where they are interpreted and acted upon. These hormones bind to their specific receptors on the target organ. Hormones trigger responses from organs or tissues that have been programmed to respond to them. Hormones slowly and over time affect the body's growth, development, metabolism, sexual function, and mood. Multiple diseases are caused when the endocrine glands underproduce (or do not produce at all) or overproduce a hormone.

What Is the Gastrointestinal Tract?

The gastrointestinal tract is the digestive path that connects the mouth to the anus. The GI tract houses the digestive system's major organs, including the esophagus, stomach, and intestines. Food is absorbed through the mouth and digested to extract nutrients and energy, with waste being ejected through the anus. The gastrointestinal tracts are divided into upper and lower gastrointestinal tracts. It also includes the tongue, salivary glands, pancreas, liver, gallbladder, and accessory digestive organs. In addition, several hormones are secreted from digestive organs into the digestive tract that aid in several processes, including digestion and absorption of food.

What Are the Hormones of Gastrointestinal Tract?

The gastrointestinal hormones, also known as the gut hormones, are a class of hormones secreted in various parts of the gastrointestinal tract and responsible for the functioning of the digestive organs. These hormones are interconnected, and their production may rise or decrease in response to various clinical conditions, resulting in digestive system dysfunction. Gastrointestinal hormones are peptides (a short chain of amino acids), and they are secreted by the cells lining the inside space of the stomach and small intestine. These cells that secrete gastrointestinal hormones are known as endocrinocytes, a type of epithelial cell. Many gastrointestinal hormones are also produced in the brain, which is why they are also frequently referred to as brain-gut peptides. Gastrointestinal hormones are released into the bloodstream and circulate throughout the body, influencing the functioning of various portions of the digestive tract, the liver, the pancreas, the brain, and several other organs.

What Is Gastrin and Its Functions?

Gastrin is a gastrointestinal hormone that stimulates gastric acid secretion, which means food movement in the gastrointestinal tract. The peptides stimulate the gastrin release in the stomach's inner part (lumen).

Gastrin induces the stomach to secrete HCL (gastric acid), which is necessary to convert pepsinogen, a protein-digesting enzyme, into its active form, pepsin.
Gastric acid assists the stomach in breaking down and absorbing various vitamins, including vitamin B12.
Gastric acid, secreted by gastrin, works as a disinfectant, killing most germs and microbes that enter the stomach accompanying food, thereby reducing the risk of infection in the gastrointestinal tract.
Gastrin triggers the gallbladder to empty its bile reserve.
Gastrin also stimulates the pancreas to release enzymes.
Gastrin also aids digestion by stimulating stomach lining growth and increasing gut muscle contractions.

What Is Cholecystokinin and Its Functions?

Cholecystokinin is a gastrointestinal hormone secreted by the I-cells in the lining of the first part of the small intestine (duodenum). Cholecystokinin works on two receptors in the gut and the nervous system. Because of its activities on the pancreas, cholecystokinin was previously known as pancreozymin. Functions of cholecystokinin include:

This hormone's most well-known roles are in digestion and appetite.
It aids digestion by delaying the emptying of food through the stomach.
Cholecystokinin stimulates bile production in the liver and bile release from the gallbladder.
Cholecystokinin also stimulates the pancreas to release enzymes that help the metabolism of fats, proteins, and carbohydrates.
Finally, cholecystokinin appears to play a role in appetite by increasing the sense of fullness within a short time.

What Is Secretin and Its Functions?

Secretin, a hormone of the gastrointestinal tract, is responsible for water regulation in the whole body and influencing the environment of the first part of the small intestine (duodenum). The acidic pH of the small intestine regulates the release of secretin. Prosecretin is a precursor to secretin, and secretin is stored in this inactive state until gastric acid activates it. Secretin is produced by the S-cells present in the duodenum. The several functions of secretin include:

Secretin aids in maintaining the pH of the small intestine by blocking the secretion of gastric acid and triggering the production of bicarbonates.
Water and bicarbonate secretion from the pancreas and bile ducts are stimulated by secretion.

What Is Ghrelin and Its Functions?

Ghrelin is a gastrointestinal hormone synthesized and secreted chiefly by the stomach, and it is also released in small amounts by the small intestine, the pancreas, and the brain. Ghrelin is also known as the hunger hormone produced by the specialized gastrointestinal tract cells. It is also known as the hunger hormone because it increases the drive to eat. The ghrelin levels are highest before eating and exponentially fall after eating. Various functions of ghrelin include:

Ghrelin's primary role is to control energy homeostasis, which is described as the act of coordinated homeostatic regulation of energy inflow (through food intake) and energy outflow (through energy expenditure).
Due to its regulatory effect on energy homeostasis, ghrelin also plays a role in regulating body weight.
Ghrelin is also crucial for stimulating the release of growth hormones.
Ghrelin is also crucial for the regulation of the sleep-wake cycle. Ghrelin production has been shown to be affected by sleep deprivation.
Ghrelin also has a role in the perception of taste.

What Is Motilin and Its Functions?

Motilin is a gastrointestinal tract hormone released by the endocrine Mo cells or M cells of the upper part of the small intestine (duodenum). The release of motilin is stimulated by fasting. Motilin is unrelated to other hormones regarding the different amino acid sequences. Motilin is released in cycles at about 100-minute intervals during fasted or inner digestive states. The functions of motilin include:

Stimulation of pepsin production.
Improves the peristaltic movement (muscle contraction and relaxation) of the gastrointestinal tract and empties the stomach for the next meal.
Increases the insulin release from the pancreas.
Increase hunger or appetite.
A high level of motilin secreted between meals causes the stomach's upper and end parts to contract, speeding up gastric emptying.

What Is Gastric-Inhibitory Peptide and Its Functions?

The gastric-inhibitory peptide is a gastrointestinal tract hormone belonging to the secretin family. This hormone is also known as the glucose-dependent insulinotropic polypeptide. It is a potent insulin stimulator and weak acid secretion inhibitor after meals. K cells, which are present in the mucosa of the duodenum and the jejunum, are responsible for the production of this hormone. The various functions of gastric-inhibitory peptides are:

When present at higher levels, it helps reduce gastric acid production to protect the small intestine from acid damage.
Induction of insulin secretion.
Prevent death of pancreatic beta cells.
Promote division and growth of the pancreatic beta-cells.
Stimulation of glucagon secretion.
Fat accumulation.

Conclusion:

Hormones of the gastrointestinal tract are crucial for several digestive and other functions. Any imbalance in their level can cause multiple problems, including; indigestion, reduced movement of the gastrointestinal tract, reduced food motility, improper release of insulin, diarrhea, nausea, pain in the abdomen, stomach ulcers, constipation, etc. Therefore, it is essential to keep a check on the levels and proper functioning of these hormones. In addition, these hormones can also stimulate problems in various other parts of the body, including the nervous system and the reproductive system.

Frequently Asked Questions

1. What Hormones Does the Gastrointestinal Tract Generate, and What Roles Do These Hormones Play?

Hormones produced by the gastrointestinal system include ghrelin, gastrin, secretin, and cholecystokinin (CCK). Gastrin increases the production of stomach acid, whereas CCK causes the pancreas to release digestive enzymes and the gallbladder to release bile. To counteract stomach acid, the pancreas releases bicarbonate when secretin activates it. The hunger hormone, or ghrelin, affects energy balance and increases appetite.

2. What Is the Effect of the Release of Gastrointestinal Hormones on the Processes of Digestion and Absorption?

Digestion and absorption are significantly affected by gastrointestinal hormone secretion. These hormones, which include secretin, cholecystokinin (CCK), and gastrin, control the production of digestive enzymes and the release of bile, which improves the stomach's and small intestine's ability to break down nutrients. Furthermore, they control nutrition absorption and stomach emptying, promoting effective nutrient uptake and preserving digestive homeostasis.

3. What Functions Does Gastrin Serve in the Gastrointestinal Tract, and What Mechanisms Control Its Activity?

Gastrin stimulates the release of gastric acid, which aids in digestion, and plays a vital function in the gastrointestinal system. It is predominantly made by stomach G cells and released in reaction to the presence of food. The action of the hormone gastrin is precisely controlled by several variables, including the pH of the stomach, the presence of peptides and amino acids, and neurological impulses.

4. What Impact Do Ghrelin Levels Have On Appetite and the Regulation of Weight?

Ghrelin, the hormone known as the "hunger hormone" affects appetite and influences weight maintenance. The brain receives a signal of hunger when ghrelin levels rise, which promotes eating more. As high ghrelin levels can lead to overeating and possible weight gain, this hormonal interaction is crucial for preserving body weight and energy balance.

5. What Role Does Cholecystokinin (CCK) Play in the Gastrointestinal Hormonal System?

In the gastrointestinal tract, cholecystokinin (CCK) is a vital hormone that is primarily secreted from the small intestine in response to the presence of proteins and lipids. Its primary function is to trigger the gallbladder's contraction and the pancreas' production of digestive enzymes, which aid in the emulsification and absorption of lipids. Furthermore, CCK serves as a satisfaction signal that controls the size of the meals.

6. In What Way Does the Hormone Secretin Participate in the Digestive Processes of the Stomach and Pancreas?

In the stomach and pancreas, secretin is essential for digestive functions. It is released from the small intestine in reaction to the stomach chyme's acidity, which causes the pancreas to produce secretions high in bicarbonate. By ensuring that nutrients are effectively absorbed in the digestive system and fostering an environment that is favorable to the activity of digestive enzymes, this bicarbonate secretion helps counteract the acidic chyme that enters the small intestine.

7. What Is the Function of Motilin in Regulating Gastrointestinal Motility?

The Motilin hormone plays a major part in controlling gastrointestinal motility. It operates on smooth muscle cells in the stomach and small intestine, stimulating contraction and aiding the passage of food through the digestive system. It is mostly secreted during fasting times. Through the stimulation of peristaltic activity, motilin helps to maintain the normal transit and digestion of food by improving the overall efficiency and coordination of gastrointestinal motility.

8. In What Way Do Hormones Such as Glucagon-like Peptide-1 (GLP-1) Participate in Glucose Metabolism?

The metabolism of glucose is significantly influenced by hormones such as glucagon-like peptide-1 (GLP-1). When food is consumed, the gut releases GLP-1, which increases insulin production and encourages cells to absorb glucose. Furthermore, GLP-1 suppresses the release of glucagon, which lowers the liver's synthesis of glucose. These coordinated activities play a major role in the management of diseases like diabetes and help maintain glucose homeostasis.

9. What Role Does Peptide YY (PYY) Play in Suppressing Appetite and Inducing Satiety?

Peptide YY (PYY) plays a key role in promoting fullness and suppressing hunger. PYY is a hormone that is released by the digestive system in reaction to food consumption, specifically fats. It tells the brain to decrease hunger and increase feelings of fullness. This hormonal balance aids in regulating food consumption, which helps maintain a healthy energy balance and regulate weight.

10. In What Manner Do Levels of Vasoactive Intestinal Peptide (VIP) Impact Blood Flow within the Gastrointestinal Tract?

Blood flow in the gastrointestinal system is significantly controlled by levels of the protein called vasoactive intestinal peptide (VIP). VIP is a vasodilator that helps blood vessels relax. It is secreted by smooth muscle cells and enteric neurons. By improving blood flow, this vasodilation supports sufficient food delivery and perfusion to the gastrointestinal tissues, which promotes the best possible digestive performance.

11. Which Hormones Are Linked to the Control of Acid Secretion in the Stomach?

The control of stomach acid output is influenced by many hormones. The stomach lining's G cells produce gastrin, which increases the production of gastric acid. D cells secrete somatostatin, which functions as an inhibitor to reduce the release of acid and gastrin. Furthermore, histamine interacts with parietal cell histamine receptors to promote acid production when it is produced by enterochromaffin-like cells. The exact regulation of stomach acid levels is ensured by the hormones' balanced interaction.

12. What Is the Role of Enteroendocrine Cells in the Secretion of Gastrointestinal Hormones?

The release of hormones related to digestion is mostly dependent on enteroendocrine cells. These cells, which are dispersed throughout the intestinal lining, react to a variety of stimuli, including the presence of nutrients and mechanical stretching of the gut. Enteroendocrine cells are stimulated to release hormones that affect digestion and maintain the balance of body reactions to food. These hormones include secretin, cholecystokinin (CCK), and gastrin. The control of nutrition absorption, digestion, and general gut homeostasis depends on this hormonal communication.

13. What Elements Impact the Release of Gastrointestinal Hormones?

Numerous variables affect the production of hormones related to the digestive system. Hormones, including gastrin, cholecystokinin (CCK), and glucagon-like peptide-1 (GLP-1), are released by enteroendocrine cells in response to the presence of nutrients, especially proteins, lipids, and carbohydrates. Hormone release is also influenced by mechanical factors, such as the stretching of the gut wall during food transit. The secretion of gastrointestinal hormones is further modulated by neural signals and feedback mechanisms, which guarantee a coordinated and adaptive response to the dynamic situations inside the digestive system.

14. In What Way Does the Communication between the Gut and the Brain Impact the Secretion of Gastrointestinal Hormones?

The regulation of the secretion of gastrointestinal hormones is significantly influenced by the gut-brain axis. Immune, hormonal, and neuronal signals are involved in the gut-brain system's bidirectional connection. The brain receives sensory information from the gastrointestinal system, such as the detection of nutrients and mechanical stimulation. The brain then controls the release of hormones such as ghrelin, cholecystokinin (CCK), and peptide YY (PYY). This complex interaction maintains the equilibrium of physiological reactions to food consumption, including digestion, hunger, and gut homeostasis in general.

15. What Function Do Gastrointestinal Hormones Serve in the Assimilation of Nutrients?

The gastrointestinal tract's hormones are essential for the absorption of nutrients. By inducing the release of bile and digestive enzymes, cholecystokinin (CCK) facilitates the breakdown of lipids for absorption. Moreover, glucose uptake and metabolism are influenced by insulin and glucagon-like peptide-1 (GLP-1), which guarantees effective absorption of carbohydrates. The coordinated function of these hormones aids in the best possible absorption of nutrients from meals in the digestive tract.

Sources

Dr. Ghulam Fareed

Medical Gastroenterology

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