Gastrin & Gastrointestinal Hormones: Overview & Function

Joanna Tatomir, Artem Cheprasov
  • Author
    Joanna Tatomir

    Joanna holds a PhD in Biology from the University of Michigan and is currently working towards a degree in Veterinary Medicine at Michigan State University. She has taught a combination of ESL and STEM courses to secondary and university students.

  • Instructor
    Artem Cheprasov

    Artem has a doctor of veterinary medicine degree.

Learn the definition of gastrointestinal system and gastrointestinal hormones. Discover how gastrin and other digestive hormones are secreted and function. Updated: 11/21/2021

Gastrointestinal Definition

The gastrointestinal tract represents a key component of the digestive system. Whenever humans eat vegetables, fruits, or animal products, these foods are processed in the organs of the gastrointestinal tract (GI tract). The gastrointestinal tract stretches from the mouth to the anus and includes the following organs:

  • Mouth
  • Esophagus
  • Stomach
  • Liver and Gallbladder
  • Pancreas
  • Small and Large Intestines
  • Rectum
  • Anus


The human digestive system.

Gastrointestinal definition


The mouth starts the process of breaking down foods for the absorption of nutrients needed to fuel the body's activities. From the mouth, food passes down the esophagus and enters the stomach, where additional food processing occurs. As the food moves from the stomach to the small intestine, hormones regulate enzyme release in the organs of the gastrointestinal tract. These enzymes help to break down foods into their substituent sugars, lipids, and proteins, which are then absorbed by the intestines and transported throughout the body for use in the production of energy. This energy is then used to create new cells and tissues throughout the body.

In this lesson, the hormones of the gastrointestinal tract will be examined in terms of their secretion and functions within the human body.

What Are Gastrointestinal Hormones?

Besides water and air, what else do you need in order to live a healthy life? Nope, not your phone, but good guess. It's food. Your body needs food as a source of fuel to power all of its processes.

But the food doesn't magically enter your body's cells. It needs to be digested thanks to the gastrointestinal system, a collection of cells, tissues, organs, and biochemicals that allow for the digestion and absorption of food into the body.

Those biochemicals, at least some of them, are what this lesson is about. We'll be taking a look specifically at gastrointestinal hormones, which are biological molecules that help your body digest and absorb the food that you eat.

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  • 0:04 What Are…
  • 0:45 Gastrin, Secretin, & CCK
  • 2:36 GIP, Ghrelin, & Motilin
  • 3:40 Other Hormones
  • 4:14 Lesson Summary
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Gastrointestinal Hormone

There are three basic types of gastrointestinal hormones: endocrine, paracrine, and neurocrine. Endocrine gastrointestinal hormones directly enter the human bloodstream subsequent to secretion by enteroendocrine cells located in various parts of the digestive tract. Some of the endocrine hormones examined as part of this lesson include gastrin, secretin, cholecystokinin, glucose-dependent insulinotropic peptide (GIP), and motilin.

Unlike endocrine hormones, which directly enter the bloodstream, paracrine digestive hormones are secreted by enteroendocrine cells but instead travel to nearby tissues where they act to facilitate the processes associated with digestion. Examples of paracrine digestive hormones include somatostatin and histamine. Neurocrine gut hormones are secreted by neurons located in the gastrointestinal tract and include ghrelin, which will be discussed later in this lesson, as well gastrin release peptide and enkephalins.

Some of the digestive hormones mentioned above will be further discussed below.

Gastrin Function

Gastrin represents an essential hormone responsible in part for the regulation of the digestive tract. As an endocrine hormone, gastrin is secreted into the bloodstream by specialized cells known as neuroendocrine cells. The specific neuroendocrine cells responsible for gastrin secretion are known as G cells. These cells are primarily located in the antrum of the stomach, the part of the stomach directly connecting to the duodenum, or the first part of the small intestine.

What is the function of gastrin? Gastrin has three main functions:

  • Stimulates the growth of the mucosal layers of the digestive tract
  • Facilitates the movement of food and nutrients through the GI tract, also referred to as gastric motility
  • Stimulates the secretion of hydrochloric acid by parietal cells located in the stomach

Gastrin function occurs primarily in the stomach, pancreas, and duodenum, where it is downregulated by the presence of hydrochloric acid. Downregulation refers to signals that decrease the production of a hormone. Gastrin in turn downregulates the production of secretin and GIP.

Secretin

Secretin represents another endocrine hormone which is released directly into the bloodstream. Produced by S cells found in duodenum, secretin possesses several important functions related to the digestive tract. First of all, secretin is responsible for upregulating the secretion of pancreatic bicarbonate. Upregulation refers to signals that increase the production of a hormone. Bicarbonate secretions help to neutralize the stomach acid as the processed food and nutrients leaving the stomach, also referred to as chyme, enters the duodenum. This helps to prevent damage to the small intestine due to hydrochloric acid secretion in the stomach.

In addition, secretin is responsible for osmoregulation in the GI tract. Osmoregulation refers to the maintenance of water homeostasis via the control of water absorption and excretion. For example, when there is a loss of water homeostasis in the body, secretin is secreted by the posterior pituitary. Once in the bloodstream, secretin causes the collecting ducts of the kidney to increase the absorption of water. This water is then returned to blood circulation in order to restore the proper water balance within the body.

Gastrin, Secretin, & CCK

Let's pretend you're eating a hamburger. As you swallow a piece of it, it moves from your mouth, into the esophagus (food tube), and down into the stomach. Some of the stomach's cells release a hormone called gastrin. Gastrin is released in order to tell the stomach to secrete hydrochloric acid. This acid is an important component of your stomach acid.

What's stomach acid good for? Well, two major things. First, the stomach acid helps to break the food apart a bit chemically. Second, the acid is deadly. Not to you, thankfully (at least not usually). It's deadly to all sorts of potentially harmful microorganisms that may be found in that probably not-very-well-cooked piece of hamburger meat.

The partially digested bite of hamburger moves on to the intestines. The first part of the intestines is called the duodenum. It is attached directly to the stomach. The cells of the duodenum release a hormone called secretin. Secretin has a bunch of different roles:

  • It tells the stomach to stop making so much stomach acid.

  • It helps promote the release of bicarbonate from the bile ducts. Bicarbonate is something that neutralizes the stomach acid that was just flushed into the duodenum from the stomach. Think of bicarbonate as pouring water on the fire that is stomach acid.

  • It tells the pancreas to start secreting bicarbonate juice as well, for much the same reason.

On the note of the pancreas, this is an organ that also secretes digestive enzymes. And, what do you know? There's a gastrointestinal hormone that tells the pancreas to do this. That hormone is called cholecystokinin. Thankfully it's abbreviated as CCK. CCK is also released by the cells of the duodenum, and besides stimulating the pancreas to release digestive enzymes, it also tells the gallbladder to release a substance called bile, which is essential for the digestion and absorption of fat.

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Video Transcript

What Are Gastrointestinal Hormones?

Besides water and air, what else do you need in order to live a healthy life? Nope, not your phone, but good guess. It's food. Your body needs food as a source of fuel to power all of its processes.

But the food doesn't magically enter your body's cells. It needs to be digested thanks to the gastrointestinal system, a collection of cells, tissues, organs, and biochemicals that allow for the digestion and absorption of food into the body.

Those biochemicals, at least some of them, are what this lesson is about. We'll be taking a look specifically at gastrointestinal hormones, which are biological molecules that help your body digest and absorb the food that you eat.

Gastrin, Secretin, & CCK

Let's pretend you're eating a hamburger. As you swallow a piece of it, it moves from your mouth, into the esophagus (food tube), and down into the stomach. Some of the stomach's cells release a hormone called gastrin. Gastrin is released in order to tell the stomach to secrete hydrochloric acid. This acid is an important component of your stomach acid.

What's stomach acid good for? Well, two major things. First, the stomach acid helps to break the food apart a bit chemically. Second, the acid is deadly. Not to you, thankfully (at least not usually). It's deadly to all sorts of potentially harmful microorganisms that may be found in that probably not-very-well-cooked piece of hamburger meat.

The partially digested bite of hamburger moves on to the intestines. The first part of the intestines is called the duodenum. It is attached directly to the stomach. The cells of the duodenum release a hormone called secretin. Secretin has a bunch of different roles:

  • It tells the stomach to stop making so much stomach acid.

  • It helps promote the release of bicarbonate from the bile ducts. Bicarbonate is something that neutralizes the stomach acid that was just flushed into the duodenum from the stomach. Think of bicarbonate as pouring water on the fire that is stomach acid.

  • It tells the pancreas to start secreting bicarbonate juice as well, for much the same reason.

On the note of the pancreas, this is an organ that also secretes digestive enzymes. And, what do you know? There's a gastrointestinal hormone that tells the pancreas to do this. That hormone is called cholecystokinin. Thankfully it's abbreviated as CCK. CCK is also released by the cells of the duodenum, and besides stimulating the pancreas to release digestive enzymes, it also tells the gallbladder to release a substance called bile, which is essential for the digestion and absorption of fat.

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Frequently Asked Questions

How many gastrointestinal hormones are there?

More than fifty gut hormones have been discovered thus far by researchers. Some of the major gastrointestinal hormones include gastrin, secretin, cholecystokinin, and ghrelin.

What stimulates secretion of gastrin?

Gastrin secretion is stimulated by the presence of food in the stomach, as well as by the feeling of fullness in the stomach. Gastrin secretion is also enhanced by elevated levels of gastrin-releasing peptide.

Why is gastrin important?

Gastrin represents a gut hormone responsible for the secretion of hydrochloric acid in the stomach. It is an important hormone because it regulates the overall digestive process by controlling the speed with which food is processed by the GI tract.

What are the major gastrointestinal hormones?

Gastrointestinal hormones are responsible for regulating food digestion and nutrient absorption in the human body. Several important digestive hormones include gastrin, secretin, and motilin.

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