Human Stomach – Structure and Functions

Introduction

The position of the stomach in the human body is on the left side of the upper abdomen, below the liver. Its size depends from person to person and how recently and how much the person has eaten. 

The food reaches the oesophagus through the mouth and then via the lower oesophageal sphincter (a muscular valve), it enters the sac-like muscular organ, the stomach. 

The stomach acts as a receptacle for the storage and mechanical distribution of food for a brief period of time before it makes its way into the intestine. It is divided into five regions: the cardia, fundus, body, antrum and pylorus.

The Human Body Stomach Structure

As mentioned above, the human body has five distinct sections. Let’s take a closer look at each of them. 

1. The cardia: It is the top part of the stomach and contains the cardiac sphincter. Its primary function is to not allow the food to travel back upwards to the oesophagus. 
2. The fundus: Next to the cardia is a rounded section called the fundus. It is found in the upper-left part of the stomach. The fundus is usually filled with the air that enters our stomach when we swallow. It stores the undigested food and gases released during chemical digestion. 
3. The body: The most significant section of the stomach is called the body or corpus. It contracts and mixes the food. Here, the food is churned, broken into smaller pieces, and mixed with acidic gastric juice and enzymes. 
4. The antrum: This somewhat funnel-shaped section is found below the corpus. The antrum holds the food until the stomach is ready to pass it to the small intestine.
5. The pylorus: Along with the pyloric sphincter, this is where the stomach and the small intestine connect. It controls when and how the stomach contents travel to the small intestine. 

While these were the sections, the human body’s stomach also has several tissues and muscles. The following are four of them:

1. Mucosa: It is the stomach’s inner lining. When the stomach is empty, it has small ridges. Once the stomach is complete, the mucosa expands, flattening the ridges. 
2. Submucosa: It contains blood vessels, connective tissues, nerve cells and lymph vessels. The submucosa covers and protects the mucosa. 
3. Muscularis Externa: This primary muscle of the stomach is made of three layers that help break down food by contracting and relaxing. 
4. Serosa: it is the layer of the membrane covering the stomach. 

On average, a normal human stomach can comfortably hold up to 1 litre of food. However, the holding capacity can be expanded to 4 litres maximum due to its elastic nature. This is why our stomachs expand when we overeat and contract to their standard size as and when the food gets digested. If we consistently consume more than 1 litre of food, our stomach will adjust and stretch itself to suit the required capacity. 

Functions of the Stomach

The three primary functions of the stomach are: 

1. To temporarily store food.
2. To mix and break down food by contracting and relaxing.
3. To produce enzymes and other specialised cells to digest food. 

Hydrochloric Acid and the Stomach

The stomach forms a digestive fluid called hydrochloric (HCI) acid during the digestion process. This acid plays a critical role in the process of digestion by the following process:

• The acid helps the body break down, digest and absorb proteins and nutrients
• The HCI found in the stomach aids digestion by disintegrating complex food molecules into simpler and smaller ones
• It kills the bacteria and digests the protein present in the enzyme pepsin by creating a medium of gastric juice acidic
• It also activates the pepsinogen enzyme, which is needed to digest proteins

Stomach and Gastrointestinal (GI) Tract 

The position of the stomach in the human body is such that the stomach forms a part of the GI Tract. A long tube begins at the mouth and ends at the anus, i.e., the entire length from where food enters our body to where it is excreted from. Naturally, the gastrointestinal tract is an essential part of the digestive system. 

Let’s understand how exactly food travels through the GI tract.

1. Mouth: The food enters our body through the mouth. As we chew and swallow, the tongue helps push back the food in the throat into the oesophagus. To prevent choking, the epiglottis covers the windpipe.
2. Oesophagus: As we swallow the food, it travels down a hollow tube known as the oesophagus. Here, the oesophageal sphincter (a ring-shaped muscle that loosens and tightens) relaxes and allows the food to pass into the stomach.
3. Stomach: It is a temporary receptacle that holds the food until it is ready to travel to the small intestine. Meanwhile, the stomach creates digestive juices and further breaks down the food. 
4. Small Intestine: Here, the food mixes with the digestive juices from the liver, intestine and pancreas. The intestinal walls absorb all the nutrients and water from the food. Furthermore, the waste products are sent to the large intestine.
5. Large Intestine: The waste products sent here are converted into the stool and later pushed into the rectum.
6. Rectum: It is the lower portion of the large intestine. The stool is stored here until we have a bowel movement. 

Conclusion

 Stomach is the most distensible and widest organ of the alimentary canal. It is a thick muscular J-shaped organ which is placed obliquely behind the diaphragm on the left sides. It helps in mechanical churning and chemical digestion of food. The position of the stomach in the human body is on the left side of the upper abdomen, below the liver. Its size depends from person to person and how recently and how much the person has eaten.