Which of the following is NOT a main function of the stomach?

The main functions of the stomach include storage, chyme formation, and controlling the rate at which contents are passed into the small intestine.

Storage is crucial because the stomach can hold food and gradually release it into the small intestine, allowing for efficient digestion and absorption. Chyme formation occurs as the stomach mixes and breaks down food, producing a semi-liquid mass called chyme, which is vital for proper digestion in the small intestine.

Controlling the rate of passage is also a significant function, as the pyloric sphincter regulates the flow of chyme from the stomach into the duodenum, ensuring that the digestive processes occur in a controlled manner.

While protein digestion does occur in the stomach, it is not the primary purpose of this organ, as the stomach primarily serves to begin the digestion process through mechanical and chemical means. Enzymes like pepsin, which are activated in the acidic environment of the stomach, play a role in breaking down proteins, but the stomach's role in overall digestion is broader than just protein digestion. Thus, identifying protein digestion as a main function simplifies the complexity of the stomach's roles and overlooks the more encompassing functions it performs related to food storage, mixing, and passage control.