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Stomach Definition

The stomach is an essential organ of the human digestive system, before understanding the functions of the stomach, it is important to understand the stomach anatomy, stomach definition and its structure. The stomach definition according to biology is the J-shaped thick-walled organ that lies in the digestive cavity of the body. Even though a minimal percentage of digestion occurs in the mouth, the digestive process begins in the buccal cavity itself.

The stomach connects the oesophagus to the first part of the small intestine known as the duodenum. It is an enlargement of the alimentary canal that lies directly inferior to the oesophagus. As we are going to discuss the human stomach and functions of stomach it is important to note that the primary function of the stomach is to store the bolus (bolus is the chewed food mixed with saliva from the buccal cavity), while digestion is considered as the secondary function of the stomach. 

The article deals with the comprehensive study of the stomach that includes the discussion around the stomach definition, stomach anatomy and stomach structure. The anatomical study also mentions the stomach location. The article also briefly discusses the common stomach diseases.

The Stomach Structure

Since we have developed an overview of the stomach let us look into the gross stomach anatomy or the stomach structure in the human digestive system. The stomach is divided into four sections namely, fundus, body, antrum and pylorus. The opening of the fundus or simpler terms the very beginning of the stomach is termed the cardia region. Each section of the stomach is associated with a unique function. The cardia is defined as the opening of the oesophagus to the stomach. The fundus follows the cardia, it is the dome-shaped section, it is located inferior to the diaphragm, above and to the left of the cardia.

The fundus is followed by the body of the stomach which is the main part of the stomach. The fundus is the site where the mixing and churning of bolus takes place. The Antrum is also known as pylorus antrum is the lower part of the stomach that is responsible for retaining the food into the stomach, the pylorus is the term used to define the opening of the stomach to the duodenum region of the small intestine. The pyloric sphincter is present here, it controls the movement of the bolus into the duodenum. The stomach structure diagram mentioned below will help in a better understanding of the stomach location and the sections of the stomach.

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Histology of the Human Stomach

The histology of the stomach refers to the study of the tissues of the stomach, in simpler terms it refers to the discussion of the layers of the stomach wall and the different cells of the stomach. As discussed earlier the stomach is a J-shaped thick-walled organ, this thickness is because of multiple layers of the stomach wall. It is also important to note that each section of the stomach consists of a different subset of cells that perform a unique function in the human digestive process. 

The stomach wall has four different layers of tissue namely, the mucosa, submucosa, muscularis externa and the serosa, it is interesting to note that this scheme of tissue organisation is followed throughout the digestive system. 

  • The mucosa is the innermost layer of the stomach, it is responsible for the mucous secretion. One of the characteristic features of the mucosa is ridges when the stomach is filled with bolus it flattens the ridges.

  • The submucosa is the layer after the mucosa, it consists of large blood vessels and lymph vessels, it is the layer that is associated with nerve cells and fibres.

  • The muscularis layer is the layer above the submucosa, it is further divided into longitudinal and circular smooth muscles. The nerve plexus between the longitudinal and the circular muscles of muscularis is termed the Myenteric or Auerbach nerve plexus.

  • The serosa is the outermost layer that constitutes the fibrous membrane, it is also referred to as the visceral peritoneum.

The image mentioned below of the stomach anatomy will help in better understanding the histology and stomach structure.

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Cells of the Stomach

Since we have studied the stomach definition and stomach location or stomach position, let us look into the cells of the human stomach which are responsible for the digestive functions of the stomach. The epithelial lining of the gastric mucosa is composed exclusively of superficial mucous cells that secrete a protective coating of alkaline mucus. Numerous gastric pits are scattered on the surface of the epithelium and look like commonly used pincushions, indicating the entrance to each gastric gland that secretes a complex digestive juice called gastric juice. Let us look into the cells of the stomach.

  • Goblet cells are mucous secreting cells. They are found in the fundus and pyloric region of the stomach, the mucus provides protection against the hydrochloric acid of the stomach.

  • Parietal cells are also known as oxyntic cells, they are responsible for HCl secretion, they also secrete peptides known as the intrinsic factor. Parietal cells are present in the body and antrum region of the stomach.

  • Chief cells are found in the body and the antrum region. They are exocrine cells of the stomach, they are responsible for the secretion of pepsinogen and gastric lipase. Pepsinogen is the inactive form of pepsin that gets activated by HCl. The pepsin breaks proteins into peptones and proteases.  The gastric lipase breaks the first and third bonds of fatty acids. 

  • Endocrine cells are also found in the body and the antrum region, they are divided into two subsets G cells, concerned with gastrin release and D cells, responsible for somatostatin release. Gastrin is the ligand that induces the release of gastric acid. Somatostatin is the inhibitory hormone that inhibits the release of gastric acid.

The Stomach Diseases

There are various common stomach infections that occur as a result of the dysfunction of the cells of the stomach. Some of the common stomach diseases are mentioned below.

  • Gastritis is a stomach infection in which the organ gets inflamed, the inflammation results in severe pain and discomfort. This is generally caused by the use of alcohol. A bacteria named H.pyroli can also cause it.

  • Gastroesophageal reflux disease is a common condition in which acid-containing stomach contents can regurgitate the oesophagus. Symptoms may not appear, or heartburn or cough may occur due to regurgitation.

  • Zollinger-Ellison Syndrome (ZES) is a condition in which several tumours are formed in the stomach. The tumours secrete hormones to increase acid production. Severe GERD (Gastroesophageal reflux disease) and gastric ulcers result from this rare condition.

  • Varicose veins are a condition in people with severe liver disease that can cause the veins in the stomach to swell and swell when pressure is increased. These veins, called varicose veins, patients suffering from it have an increased risk of bleeding.

  • A stomach ulcer, also known as gastric ulcer, is an erosion of the mucosal lining of the stomach that often causes pain and bleeding. Gastric ulcers are most commonly caused by NSAID (non-steroidal anti-inflammatory drugs) or H. pylori infections.

To conclude, we have learnt about the stomach digestive system and the components involved in the functions of the stomach. We have also learnt about common stomach disorders.

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FAQs on Stomach

1. What is chyme?

Ans: Chyme is defined as the processed bolus. Bolus is the food content and the salivary enzymes, as the bolus enters into the stomach it gets mixed with the gastric juices and HCl and gets further digested, this partially digested form of the bolus is known as a chime. Chime enters into the small intestine through the pyloric sphincter.

2. What is the site of mechanical digestion apart from the buccal cavity?

Ans: The stomach also performs mechanical digestion. The stomach walls create a wave that assists in breaking the food particle, secondly, it helps in better interaction of the gastric juices with the food. This process is often known as mechanical churning of the stomach. The churning is followed by gastric emptying which refers to the exit of food into the duodenum.