What is the stomach made of and how does it work?

The stomach is a wonderful organ with unique characteristics and important functions for digestive health. We explain here how it works and how to take care of it.

Last update: August 29, 2021

The stomach is a compliant J-shaped organ located in the upper left quadrant of the abdomen. Can expand 50 times its size compared to when it is empty.

It changes in size, shape, and position depending on the person's posture and whether or not they are full. In an adult, its average capacity is 1.5 liters.

Its main functions are to receive, store and soften the ingested food, turning it into a liquid mixture. It then releases it into the duodenum in appropriate amounts. In parallel, hydrochloric acid and secreted enzymes that make up gastric juice have the important mission of neutralizing harmful bacteria and start the digestion of proteins.

What happens in the stomach when eating?

Fasting, a minimum gastric juice production is maintained. Before eating food, hunger, the visualization and smell of it will increase the production of gastric juice and that the stomach prepares itself to receive the food. This is known as cephalic phase of digestion and it is responsible for approximately 30% of gastric juice production.

Once we start eating and the food reaches the stomach, the organ relaxes and becomes distended. Enzyme appears pepsin and gastric juice secretion is stimulated. This is the gastric phase of digestion, which lasts between 2 and 3 hours.

The stomach is mainly made up of involuntary smooth muscle. In conjunction with the secretion of substances, motility increases. These rhythmic movements promote chemical digestion, by facilitating the mixture between food and the substances produced. It results in mechanical digestion. Both processes convert food into chyme.

When the food passes into the duodenum, the stimuli present in the previous phases cease and the secretion of gastric juice returns to its initial state. In this, the intestinal phase of digestion, the remaining 10% of gastric juice is produced.

The stomach is not a nutrient absorption area. There is minimal absorption of the initial products of protein digestion and none of the fats. However, simple sugars, water, and alcohol are absorbed.



Other functions of the stomach

The acidic stomach environment allows ionization of ingested calcium, so that it is later absorbed in the intestine. In this way, the stomach plays a key role in bone health.

Stomach secretion is necessary for the absorption of iron, magnesium, vitamin B12, and ascorbic acid. At the same time, the stomach participates in the control of appetite and obesity. It does this through the production of substances that interact with the fibers of the vagus nerve.

On the other hand, the stomach it is a complex organ in its immune part. It plays a crucial role in defense against microorganisms present in ingested food.

The production of hydrochloric acid is mediated by various substances and stimuli.


Structure of the stomach

The stomach is divided into 3 main parts: fundus, body and pyloric region. The fundus of the stomach is the largest, most distensible part that contains the parietal cells inside.

The stomach borders in the upper part with the abdominal portion of the esophagus, with which it communicates through the cardia. In the lower one, with the duodenum, with which it communicates through the pylorus.

Due to its location, it is also related to other organs, such as the liver, pancreas, spleen, transverse colon, kidney, and the left adrenal gland.

Layers and cells of the stomach

The stomach wall is divided into 4 overlapping layers:

  • Mucous membrane: the innermost, covered by the epithelium. It contains 35 million small depressions called crypts, which produce about 2 liters of gastric juice a day.
  • Submucosa: it has a rich capillary circulation.
  • Muscular.
  • Serous: the outermost, which is the part of the peritoneum that lines the stomach.

The gastric crypts are lined by the following types of cells:

  • Mucous: responsible for producing abundant mucus to protect the stomach lining.
  • Parietal or oxyntic: they secrete hydrochloric acid that is responsible for chemical digestion and sterilization of food. In addition, they produce intrinsic factor, a transporter protein for vitamin B12.
  • Main cells: They secrete inactive pepsinogen which, when exposed to hydrochloric acid, will be converted to the active enzyme pepsin. They also produce gastric lipase, which continues the digestion of fats initiated by lingual lipase.
  • Endocrine cells: they synthesize hormones, such as gastrin and histamine, which increase the secretion of gastric juice. Somatostatin and ghrelin too.

Why doesn't the stomach digest itself?

The acidic pH and pepsin could damage the gastric mucosa. However, it is capable of withstanding numerous attacks of various origins.

Multiple factors intervene to avoid or cushion this risk. The main one is a mucus and bicarbonate gel that acts as a barrier, separating the gastric mucosa from the stomach contents.

Another factor involved is the remarkable ability to repair the epithelium when injured. As well as the production of substances called prostaglandins, capable of improving acid resistance, activating mucus and bicarbonate secretion.

An additional protective line is the rich vascular bed of the submucosa., through which the bicarbonate that mucous cells need to neutralize gastric acidity circulates. At the same time, oxygen and micronutrients contribute to cell repair.

What happens if this protection fails?

The gastric wall faces the impact of numerous circumstances capable of causing damage and inflammation of its mucosa (gastritis). Some of these lesions are produced by microbes, being the most prominent being infection by Helicobacter pylori.

Other injuries are autoimmune or allergic in nature. At the same time, there are harmful chemical agents, such as non-steroidal anti-inflammatory drugs o NSAIDs, among which is aspirin.

Sustained erosion of the mucosa can lead to atrophy or loss of parietal cells and secondary anemia. If this process continues, gastric cancer can occur.

Another consequence of the persistent imbalance between the acidity of the stomach contents and the protective mechanisms is the development of gastric mucosa tears. They receive the name of ulcers.

The acid secretion of the stomach also intervenes in the presentation of diseases beyond this organ. This is how gastroesophageal reflux can lead to erosive esophagitis and even esophageal cancer.

The bacteria H. pylori it is a risk factor for gastritis and even stomach cancer.

Tips for caring for digestive health

The health of the stomach is of great importance. Here we tell you what actions you can take to take care of this organ.

Give up smoking

Smoking is associated with lung cancer. But in fact, is a major risk factor for ulcers gastric and duodenal. Also for stomach cancer.

Responsible use of medicines

Self-medicating is a very risky practice. All drugs have potential adverse effects.

Commonly used over-the-counter medications, such as aspirin, naproxen, and piroxicam, can be very damaging to the stomach. For that reason, should not be used in excess and without consultation with a doctor.

Medications that inhibit or hinder acid production, such as omeprazole or ranitidine, should be used under medical supervision. Since the maintenance of the acidic environment within the stomach has crucial functions for health.

Other measures

Other measures recommended by the Spanish Foundation for the Digestive System to prevent cancer are avoiding obesity, exercising daily, consuming plenty of fruits and vegetables, and moderate alcohol consumption.

Take care of your stomach

Taking care of the stomach is not just avoiding heavy meals or slow digestion. All healthy lifestyle-enhancing habits help reduce the risk of gastritis, gastroesophageal reflux, and cancer.

See a gastroenterologist if you have symptoms relevant in your abdomen or in any part of the digestive system. Do not let the time pass by.