It's not quite accurate to say there are only four major functions of the human body. The body is incredibly complex and its functions are interconnected. However, we can categorize the body's activities into four broad areas:

1. Movement: This includes everything from walking and running to internal processes like digestion and blood flow. The muscular and skeletal systems work together for external movement, while the circulatory and digestive systems handle internal movement.

2. Respiration: This is the process of taking in oxygen and releasing carbon dioxide. The respiratory system (lungs, airways) handles this vital exchange, and the circulatory system transports oxygen throughout the body.

3. Nutrition: This encompasses all processes related to obtaining and using nutrients. The digestive system breaks down food, the circulatory system transports nutrients, and the cells use these nutrients for energy and growth.

4. Regulation: This is the body's way of maintaining a stable internal environment (homeostasis). This involves many systems working together, including the nervous system (sensing and responding to changes), the endocrine system (hormonal regulation), and the circulatory system (transporting signals and maintaining fluid balance).

These four categories are interconnected and constantly interacting. It's important to remember that the human body is a complex system with many interwoven functions.