Stomach: Anatomy, Structure, Location & Functions

Food is one of the basic requirements of human beings. Our body gets energy from the food which is required to run the metabolic processes in the body. However, the food we eat is in complex form and it needs to be converted into a simpler form and this breakdown of complex food into simpler absorbable form is known as Digestion. The human digestive system is called the alimentary canal. The alimentary canal consists of all the glands and organs involved in food processing from mouth to anus, where stomach plays a major role in the alimentary canal. In this article, we will see the process of digestion in the stomach and the role of the stomach in the process of digestion.

Read More About Difference Between Catabolism and Anabolism

Key Takeaways: Stomach structure, Gut lining tissues, enzymes releasing cells, castle intrinsic factor, pepsinogen.

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The Stomach Structure

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The stomach is a muscular, wide, J-shaped organ placed on the left side in the upper part of the abdomen just below the diaphragm. It is about 30 cm long and 15 cm wide. Stomach is the first place where the food gets stored for some time and is made up of layers of muscle i.e., three layers of smooth muscles:

1. Outer longitudinal
2. Middle circular
3. Inner oblique fibers

These muscles help in the functioning of the stomach. Churning of food is the process of mixing food with the Gastric enzymes present in the stomach.

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Parts of Stomach

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The stomach has four parts- cardiac, fundus , body and pyloric.

(a) Cardiac  - It is the broad upper region of the stomach where the oesophagus opens. The opening is called the cardiac aperture and opening consists of a valve which is called the cardiac sphincter. The sphincter guards the opening of the stomach and closes when the stomach is full, However, the cardiac sphincter is less effective in infants.

(b) Fundus - It is the region just above the cardiac part and is small, dome-shaped. This region mostly remains empty hence it often contains gas.

(c) Body - The middlemost part of the stomach is called body.

(d) Pyloric - This is the lowermost region of the stomach. It consists of a wide pyloric antrum and a narrow pyloric canal. The passage which transfers food from the stomach to the small intestine is called the pyloric canal. The pyloric canal is guarded by a valve which is known as the pyloric sphincter, this valve regulates the passage of food into the intestine.

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Layers of the Stomach

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The wall of the stomach is made up of different kinds of tissues. It consists of 4 different layers, the serosa, mucosa , submucosa and muscularis.

1. Mucosa - It is the innermost layer having ridges. As the name suggests this layer secretes mucus in the stomach. This creates a layer of mucous inside the stomach which prevents stomach ulcers as the pH of the stomach becomes acidic due to the presence of digestive enzymes.
2. Sub-mucosa - The layer after mucosa is the submucosa, it consists of lymphatic and blood vessels.
3. Muscularis - This layer consists of other two types of layer, longitudinal and circular. It consists of the muscles which help the stomach in completing the process of churning. It is made up of smooth muscles.
4. Serosa - it is the outermost layer of the stomach which is made up of thin mesothelium with some connective tissues. 

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Stomach Enzymes

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Various types of enzymes and digestive juices are secreted or mixed in the stomach for the breakdown of food. 

• The inner lining of the stomach is covered by a layer of mucous. This safeguards the stomach from the hydrochloric acid present in the stomach. Mucus is secreted by goblet cells.
• HCL is the main acidic enzyme that is secreted by oxyntic cells in the body region of the stomach. Along with HCL peptides are also secreted by oxyntic cells
• Pepsinogen is a type of protein-digesting enzyme, it is secreted by chief cells in the stomach. It is present in inactive form but later becomes active after contact with HCL.
• Certain hormonal juices are also secreted in the stomach by the endocrine cells. These juices stimulate the gastric glands to release the gastric juices.

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Function of Stomach

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The stomach serves four main functions.

1. It acts as a storage for food. Food is stored in the stomach for hours, it keeps on expanding to create room for food due to its elastic nature.
2. It secretes different types of juices and enzymes responsible for digestion. It secretes a very essential protein “Castle intrinsic factor” which helps in the digestion of vitamin B12 .
3. Mechanical churning of food is required for mixing up food with the digestive juices, this is made possible due to the regular contraction movement of the stomach.
4. A major role of the stomach is to regulate the flow of food into the small intestine.

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Things to Remember

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• The stomach is a J-shaped sac-like structure located in the middle region of the body.
• It consists of four parts namely cardiac, fundus, body and pyloric.
• The cardiac sphincter guards the opening of the stomach.
• The pyloric canal is guarded by a valve which is known as the pyloric sphincter, this valve regulates the passage of food into the intestine.
• The wall of the stomach is made up of different kinds of tissues. It consists of 4 different layers, the serosa, mucosa , submucosa and muscularis.
• The most important enzyme released by the stomach is the “Castle intrinsic factor” which helps in the digestion of vitamin B12.

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Previous Year Questions

1. Food is moved along the alimentary canal by the contraction known as... [JIPMER 2003]
2. A baby boy aged two years is admitted to play school and passes through a dental check - up. The dentist observed that the boy had twenty teeth. Which teeth were absent?… [NEET 2017] 
3. Which cells of "Crypts of Lieberkuhn" secrete antibacterial lysozyme​?... [NEET 2017] 
4. Secretin and cholecystokinin are digestive hormones. They are secreted in….​[NEET 2005]
5. Which of the following statements is not correct?... [NEET 2015]
6. If for some reason the parietal cells of the gut epithelium become partially non-functional, what is likely to happen?​... [NEET 2010]
7. The characteristic that is shared by urea... [KCET 2009]
8. The primary dentition in humans differs from... [NEET 2015]
9. Stool of a person contain whitish grey colour due to... [NEET 2002]
10. Jaundice is a disorder of​... [NEET 2010]
11. Duodenum has characteristic Brunner's gland which secrete two hormones called​...[NEET 2004]
12. A healthy person eats the following diet-5 gm raw sugar,. 4 gm albumin, 10 gm pure buffalo ghee adultrated with 2 gm vegetable ghee (hydrogenated vegetable oil) and 5 gm lignin. How many calories he is likely to get?​...[NEET 2013]
13. A person who is eating boiled potato, his food contains the component​...[NEET 2000]
14. Anxiety and eating spicy food together in an otherwise normal human, may lead to​...[NEET 2012] 
15. Calcium deficiency in the body occurs in the absence of​...[NEET 1994]
16. Choose the correct enzyme - substrate pair... [NEET 1996]
17. Continuous bleeding from an injured part of body is due to deficiency of​...[NEET 2002]
18. Duct leading from parotid gland and opening into vestibule is​...[NEET 1998]
19. During prolonged fastings, in what sequence are the following organic compounds used up by the body...[NEET 2003]
20. Emulsification of fat is carried out by​...[NEET 1990]

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