Which of the following organs is classified as a secondary organ?

The stomach is classified as a secondary organ in the context of certain systems in the body, particularly the digestive system. Primary organs are typically those that are directly involved in the main function of a system, whereas secondary organs may play supportive or supplementary roles. In digestion, for example, the primary organs include the mouth, esophagus, intestines, and other structures through which food directly passes. The stomach, while crucial for food processing, acts as a reservoir and has a specific role in digestion, often regarded as supplementary compared to the primary actions taking place before and after it in the digestive tract.

In contrast, the heart, brain, and lungs are considered primary organs within their respective systems: the heart is essential for circulatory function, the brain is central to the nervous system, and the lungs are critical for respiratory processes. Their primary roles make them fundamentally vital for maintaining homeostasis and other bodily functions, distinguishing them from the supportive role of the stomach in the digestive process.