The stomach is a muscular, elastic, pear-shaped bag, lying crosswise in the abdominal cavity beneath the diaphragm. Its main purpose is digestion of food through production of gastric juices which break down, mix and churn the food into a thin liquid.
The stomach is situated between the oesophagus 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.
Stomach structure
The stomach can be divided into four distinct parts. These are the cardia, fundus, corpus, and pylorus.
The cardia is the first portion of the stomach and is where food content passes from the oesophagus 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.
THE STOMACH CELLS
There are four main types of cells for stomach secretions spread all over the inner surface of the stomach that help with digestion:
- 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 (An enzyme that splits proteins into peptones). 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.
FUNCTIONS OF THE HUMAN STOMACH
Temporary storage organ: It acts as a temporary storage organ. Because of this, the frequency of eating is reduced.
Secretory function: It secretes HCl and pepsin apart from other things including mucus. The G cells of pyloric region secrete gastrin hormone which is one of the GI tract hormones.
Digestive function is because of pepsin enzyme. It is a proteolytic enzyme.
Protective function is because of high acidic medium due to presence of HCl, many of the micro-organisms die. Thereby it protects the GI tract from getting invaded by the microorganisms.
Hemopoietic function is because of the intrinsic factor which is secreted by gastric glands. Intrinsic factor is essential for absorption of vitamin B12 in the ileum region.
Absorptive function is also one of the functions of stomach. Some amount of water and alcohol is absorbed in the stomach region.
Motor Functions of Stomach: The movement of stomach serves important objectives namely:
It enables the stomach to act as a temporary reservoir of food.
The movements of stomach convert solid food into a fluid paste called chyme and delivers this in small quantities to duodenum for proper digestion in small intestine.
Anatomical basis of gastric motility: The movement of stomach depends on the arrangement of smooth muscle in the wall. The arrangement is as follows:
- Outer longitudinal muscle layer.
- Inner circular muscle layer.
- Oblique muscle which is inner to the circular muscle layer and restricted to upper part of stomach.
- The muscularis mucosa present in the submucosa.
All the muscles are supplied by vagus and sympathetic fibres.
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 unnecessary 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 characterised 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 oesophageal 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.