Stomach

The stomach serves several essential functions in the digestive process:

• Storage: The stomach acts as a temporary storage reservoir for food that enters the digestive tract. It can hold and accommodate a variable volume of food, allowing for controlled release into the small intestines for further digestion.

• Mechanical digestion: The stomach's muscular walls contract and churn food, mixing it with digestive juices. This mechanical digestion process helps break down food into smaller particles, creating a semi-liquid mixture known as chyme.

• Chemical digestion: The stomach secretes gastric juice, which contains hydrochloric acid (HCl) and digestive enzymes, including pepsinogen. HCl creates an acidic environment in the stomach, which activates pepsinogen to become pepsin, an enzyme that begins the digestion of proteins by breaking them down into smaller peptides.

• Killing pathogens: The acidic environment in the stomach serves as a barrier against ingested pathogens, such as bacteria and viruses. This helps protect the body from foodborne illnesses.

• Release of chyme: The stomach gradually releases chyme, the partially digested food mixture, into the small intestines through the pyloric sphincter. This controlled release ensures that the small intestines can efficiently continue the digestive process and absorb nutrients.

The stomach consists of various components and structures:

• Cardia: The cardia is the uppermost part of the stomach that surrounds the lower oesophageal sphincter (LES), the muscular ring that separates the oesophagus from the stomach.

• Fundus: The fundus is the rounded, upper portion of the stomach, located above the cardia. It serves as a storage area for food.

• Body: The body, or corpus, is the central and largest part of the stomach. It is responsible for mixing and churning food.

• Pylorus: The pylorus is the lower portion of the stomach that connects to the duodenum, the first section of the small intestines. The pylorus contains the pyloric sphincter, which regulates the release of chyme into the small intestines.

• Rugae: The stomach's inner lining has folds called rugae, which expand to accommodate food when the stomach is full and contract during digestion.

• Gastric Glands: Gastric glands are present in the stomach lining and secrete gastric juice, which contains hydrochloric acid (HCl) and pepsinogen. These glands play a crucial role in chemical digestion.

• Mucosa: The mucosa is the innermost layer of the stomach lining and contains specialised cells that produce mucus to protect the stomach lining from the acidic gastric juices.

• Muscular layers: The stomach has three layers of smooth muscles in its wall: the longitudinal, circular, and oblique muscles. These muscles contract to mix and churn food.

• Blood vessels and nerves: The stomach is well-supplied with blood vessels to transport nutrients and nerves that control its muscular contractions and the release of gastric juices.

In summary, the stomach is a vital organ in the digestive system responsible for storing, mechanically and chemically digesting food, and regulating its release into the small intestines. It plays a central role in the initial stages of digestion, breaking down food and creating chyme, which is essential for the absorption of nutrients in the small intestines.