What is the job of stomach?

The stomach, a J-shaped organ, forms an essential component of the human digestive system. Its primary function is to receive food from the oesophagus and initiate digestion. The stomach serves several crucial roles in the digestion process:

1. Food Storage: The stomach acts as a temporary storage reservoir for ingested food. It can store and accommodate a significant amount of food, allowing for gradual processing and digestion.

2. Mechanical Digestion: Once the food enters the stomach, the stomach muscles contract and relax in a series of rhythmic movements known as peristalsis. These contractions mix the food with gastric juices and break down the larger food particles into smaller pieces, aiding the digestive process.

3. Chemical Digestion: The stomach produces and secretes gastric juices, primarily composed of hydrochloric acid (HCl) and an enzyme called pepsin. HCl creates an acidic environment that kills most ingested microorganisms, while pepsin begins the chemical digestion of proteins. Pepsin works best in an acidic environment and breaks down protein molecules into smaller peptides.

4. Chyme Formation: The stomach mixes the food, gastric juices, and enzymes continuously until it forms a semi-liquid substance called chyme. Chyme has a consistency similar to that of thick soup and is ready to move on to the next stage of digestion in the small intestine.

5. Regulation of Food Passage: The stomach's muscular wall acts as a valve that controls the passage of food from the stomach into the small intestine. It prevents the undigested food from entering the small intestine too quickly and facilitates optimal nutrient absorption.

6. Absorption of Nutrients: The stomach itself absorbs certain substances directly from the ingested food. For instance, it can absorb water, some ions (such as calcium), and certain drugs like aspirin. However, the primary absorption of nutrients occurs in the small intestine.

7. Protection and Defence: The stomach's acidic environment and the production of antibacterial substances help protect the body from harmful microorganisms that may be present in the food.

8. Regulation of Hunger and Satiety: The stomach produces hormones, including ghrelin and leptin, that regulate hunger and satiety. Ghrelin stimulates hunger, while leptin signals the feeling of fullness and satisfaction, contributing to appetite regulation and overall energy balance.

Overall, the stomach plays a crucial role in the digestion process, mechanically and chemically breaking down food, preparing it for further digestion and absorption in the subsequent parts of the digestive system.