The Stomach – Boundless Anatomy and Physiology
Boundless
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Gross Anatomy of the Stomach

The stomach is divided into four sections, each of which has different cells and functions.

Learning Objectives

Describe the gross anatomy of the stomach

Key Takeaways

Key Points

The stomach is divided into four sections: the cardiac region, the fundus, the body, and the pylorus or atrium.

The stomach is lined by a mucous membrane that contains glands (with chief cells) that secrete gastric juices.

Two smooth muscle valves, or sphincters, keep the contents of the stomach contained: the cardiac or esophageal sphincter and the pyloric sphincter.

The arteries supplying the stomach are the left gastric, the right gastric, and the right gastroepiploic branches of the hepatic, and the left gastroepiploic and short gastric branches of the lineal.

Lymphatics consist of a superficial and a deep set, and pass to the lymph glands found along the two curvatures of the organ.

The nerves are the terminal branches of the right and left urethra and other parts; the former are distributed upon the back, and the latter upon the front, part of the organ.

Key Terms

chief cell: A cell located in the stomach and parathyroid gland that secretes precursor enzymes.

pylorus: The opening in a vertebrate, including humans, at the lower end of the stomach that opens into the duodenum.

sphincter: A ringlike band of muscle that surrounds a bodily opening and constricts and relaxes as required for normal physiological functioning.

The stomach is a thick, walled organ that lies between the esophagus and the first part of the small intestine (the duodenum). It is on the left side of the abdominal cavity, the fundus of the stomach lying against the diaphragm. Lying beneath the stomach is the pancreas. The greater omentum hangs from the greater curvature.

A mucous membrane lines the stomach that contains the glands (with chief cells) that secrete gastric juices. Up to three quarts of this digestive fluid is produced daily. The gastric glands begin secreting before food enters the stomach due to the parasympathetic impulses of the vagus nerve, that also make the stomach a storage vat for that acid.

The stomach is divided into four sections, each of which has different cells and functions. The sections are:

The cardiac region, where the contents of the esophagus empty into the stomach.

The fundus, which is formed by the upper curvature of the organ.

The body, the main central region.

The pylorus or atrium, the lower section of the organ that facilitates the emptying of the contents into the small intestine.

Two smooth muscle valves, or sphincters, keep the contents of the stomach contained. They are the:

Cardiac or esophageal sphincter that divides the tract above.

Pyloric sphincter or pyloric orifice that divides the stomach from the small intestine.

The arteries that supply the stomach are the left gastric, the right gastric, and right gastroepiploic branches of the hepati;, and the left gastroepiploic and short gastric branches of the lineal. They supply the muscular coat, ramify in the submucous coat, and are finally distributed to the mucous membrane.

The arteries break up at the base of the gastric tubules into a plexus of fine capillaries that run upward between the tubules. They anatomize with each other and end in a plexus of larger capillaries that surround the mouths of the tubes and also form hexagonal meshes around the ducts.

From these the veins arise, and pursue a straight course downward, between the tubules, to the submucous tissue; they end in the lineal and superior mesenteric veins or directly in the portal vein.

The lymphatics are numerous. They consist of a superficial and a deep set, and pass to the lymph glands found along the two curvatures of the organ.

The nerves are the terminal branches of the right and left urethra and other parts, the former being distributed upon the back, and the latter upon the front part of the organ. A great number of branches from the celiac plexus of the sympathetic are also distributed to it.

Nerve plexuses are found in the submucous coat and between the layers of the muscular coat as in the intestine. Fibrils are distributed from these plexuses to the muscular tissue and the mucous membrane.

This consists of an epithelium, the lamina propria underneath, and a thin bit of smooth muscle called the muscularis mucosae. The submucosa lies under this and consists of fibrous connective tissue that separate the mucosa from the next layer, the muscularis externa.

The muscularis in the stomach differs from that of other GI organs in that it has three layers of muscle instead of two. Under these muscle layers is the adventitia, layers of connective tissue continuous with the omenta.

The epithelium of the stomach forms deep pits, called fundic or oxyntic glands. Different types of cells are at different locations down the pits. The cells at the base of these pits are chief cells that are responsible for the production of pepsinogen, an inactive precursor of pepsin, which degrades proteins. The secretion of pepsinogen prevents self-digestion of the stomach cells.

Further up the pits, parietal cells produce gastric acid and a vital substance, intrinsic factor. The function of gastric acid is two fold:

It kills most of the bacteria in food, stimulates hunger, and activates pepsinogen into pepsin.

It denatures the complex protein molecule as a precursor to protein digestion through enzyme action in the stomach and small intestines.

Near the top of the pits, closest to the contents of the stomach, there are mucus-producing cells called goblet cells that help protect the stomach from self-digestion.

The Muscularis Externa

The muscularis externa is made up of three layers of smooth muscle.

The innermost layer is obliquely-oriented: this is not seen in other parts of the digestive system. This layer is responsible for creating the motion that churns and physically breaks down the food.

The next layers are the square and then the longitudinal, which are present as in other parts of the GI tract.

The pyloric antrum has thicker skin cells in its walls and performs more forceful contractions than the fundus. The pylorus is surrounded by a thick circular muscular wall that is normally tonically constricted, forming a functional (if not anatomically discrete) pyloric sphincter that controls the movement of chyme.

Digestive Properties of the Stomach

The movement and flow of chemicals into the stomach is controlled by the autonomic nervous system and various digestive system hormones.

Learning Objectives

List the various digestive properties of the stomach

Key Takeaways

Key Points

Digestive hormones include: gastrin, somatostatin, cholecystokinin, secretin, gastric inhibitory peptide, and enteroglucagon.

Gastrin causes an increase in the secretion of HCl from the parietal cells, an increase in pepsinogen from the chief cells in the stomach, and an increase in stomach motility.

Somatostatin inhibits the activity of gastrin. Cholecystokinin (CCK) causes gall bladder contractions; it also decreases gastric emptying and increases the release of pancreatic juice that is alkaline and neutralizes the chyme. Secretin diminishes acid secretion in the stomach.

Gastric inhibitory peptide (GIP) and enteroglucagon decrease gastric acid release and motility. They also turn off stomach action when the gall bladder and liver have not yet finished absorption.

Epidermal growth factor (EGF), produced by the salivary glands, heals oral and gastroesophageal ulcers, inhibits gastric acid secretion, and stimulates DNA synthesis as well as mucosal protection.

The stomach can sense, independently to the tongue and oral taste receptors, glucose, carbohydrates, proteins, fats, and sodium glutamate via the vagus nerve, which allows the brain to link the nutritional value of foods to their tastes.

Key Terms

gastrin: A hormone that stimulates the production of gastric acid in the stomach.

antrum: A bodily cavity, especially one having bony walls, especially in the sinuses.

enteroglucagon: A peptide hormone derived from preproglucagon that is secreted from the mucosal cells, primarily of the colon and terminal ileum, that follows ingestion of a mixed meal to delay gastric emptying.

somatostatin: A polypeptide hormone, secreted by the pancreas, that inhibits the production of certain other hormones.

Examples

Gastric ulcers can be healed by supplemental daily doses of epidermal growth factor (EGF). EGF inhibits bacterial colonization and speeds healing just as well as antibiotics.

Stomach Hormones