The stomach and its role in digestion

The stomach is a muscular sac that lies between the esophagus and the small intestine in the upper abdomen. The stomach is not the only part of your digestive system that absorbs food but rather is a part of the digestive system and important for churning food into a consistency that is easier to digest for the rest of your intestines.

“Tomatoes — The stomach not only absorbs food but rather is also important for churning food into a consistency that is easier to digest for the rest of your intestines.

Function of the stomach

The stomach is J-shaped and it can expand to temporarily store food.
Partial digestion of the food takes place here. The churning action of the stomach muscles physically breaks down the food.
The stomach releases acids and enzymes for the chemical breakdown of food. The enzyme pepsin is responsible for protein breakdown.
The stomach releases food into the small intestine in a controlled and regulated manner.

Chewed food passes from the esophagus into the stomach; the flow is somewhat regulated by the esophageal sphincter but more importantly depends on how fast you eat and if you are eating both solids and liquids. The passage of food from the stomach to the small intestine is controlled by the pyloric sphincter. The crushed and mixed food is liquefied to form chyme and is pushed through the pyloric canal into the small intestine.

A network of blood vessels and nerves surrounds the stomach; this is responsible for the regulation of the secretion and the motion of stomach muscles that churns food.

The photo demonstrates the laparoscopic view of the stomach during the early stages of a sleeve gastrectomy operation. The stomach is a rather larger organ with a redundant blood and nerve supply. The two tan organs at the top of the picture are the liver on the left and the spleen on the right. The picture demonstrates the J shape of the stomach. The large blood vessels and the abrupt turn of the stomach on the left side represent the area known as both the angular incisure or incisura angularis.

The stomach can be divided into four distinct parts. These are the cardia, fundus, corpus, and pylorus.

Endoscopic view of gastric cardia and fundus

The cardia is the first portion of the stomach and is where food content passes from the esophagus into the stomach. The acids and enzymes referred to as the gastric juices are manufactured in the cardia. The fundus stores undigested food and also the gases released from the chemical digestion of food. The body of the stomach or the corpus is the largest of the four parts that make up the stomach. And this is where the bulk of the partial digestion occurs. The pylorus is connected to the duodenum or the beginning of the small intestine. The contents of the stomach move into the small intestine via the pyloric canal.

The stomach wall

The walls of the stomach consist of four layers, similar to other parts of the gastrointestinal tract. These layers, starting from the innermost layer, are named mucosa, sub-mucosa, muscularis externa, and the serosa.

The mucosa consists mainly of the gastric glands that secrete the digestive juices. It is covered by a layer of columnar epithelial tissue. The sub-mucosa consists of dense connective tissue and has blood vessels, lymphatic vessels, and nerves running through it. The sub-mucosa supports the mucosa and allows it to move in a flexible manner during peristalsis.

Peristalsis is the contraction and relaxation of the stomach muscles to physically breakdown food and propel it forward. These contractions are created by the muscular wall of the stomach which consists of inner circular and outer longitudinal smooth muscle. The outermost layer of the stomach wall, the serosa consists of an epithelial layer and connective tissue which connects to the surrounding organs. The mucosa and the sub-mucosa are present as folds termed rugae. When the stomach is distended with food, the rugae are flattened out and appear smooth.

Cell types in the stomach that help with digestion

There are four main types of cells for stomach secretions spread all over the inner surface of the stomach:

Mucous cells secrete the alkaline mucous for shielding the epithelium from hydrochloric acid. These are found in the fundic, cardiac, and pyloric region.
Parietal cells, located in the fundic, cardiac, and pyloric region, secrete hydrochloric acid; the acid activates release of pepsin for protein digestion. The acid also kills micro-organisms swallowed with the food.
Chief cells secrete pepsin. These cells are located in the fundic region.
G cells are found in the fundic, pyloric, and gastric region. These secrete gastrin which stimulates the secretion of hydrochloric acid.

Healthy habits for a healthy stomach

Certain lifestyle habits can help you maintain stomach health and also counter abdominal obesity. If you notice that certain food types do not agree with you, try to keep away from them. Limit junk food. If you experience bouts of acidity, consider adding to your diet food items that are alkaline in nature. Take walks, it aids digestion, will help you shed calories, and prevent a condition like GERD from occurring. In fact, a sedentary lifestyle with little or no exercise contributes to stomach-related problems.

Some stomach conditions and diseases

The umbrella term for stomach disease is gastropathy. Some common stomach disorders include:

Dyspepsia: This is a condition characterized by a feeling of fullness; indigestion; and pain in the upper abdomen or lower chest. Other symptoms include nausea and vomiting. Dyspepsia can be a precursor to GERD and may also indicate angina.
GERD: Gastroesophageal reflux disease is a condition in which the stomach acids rise up the esophageal passage. Heartburn is a common symptom of the condition.
Peptic Ulcers – These can occur when the protective mucous lining of the stomach walls is damaged by the stomach acids. The bacterium, Helicobacter pylori is thought to be an important factor in the development of gastric and duodenal ulcers.

Glossary