What function does the anus serve in the digestive system?

The anus serves a critical role in the digestive system by expelling undigested waste from the body. After food is consumed, it undergoes a series of processes, including digestion and nutrient absorption, which primarily occurs in the stomach and intestines. However, not all parts of the food consumed are digestible or absorbable. The remaining material, which consists of undigested food particles, fiber, and cellular debris, is eventually moved through the intestines and collected in the rectum.

When the rectum is full, signals are sent to the brain, prompting the desire to defecate. The anus opens to allow this waste to exit the body, effectively completing the digestive process. This function is essential for maintaining the body's health by eliminating materials that cannot be utilized. Therefore, the primary function of the anus is to expel this undigested waste, making it a vital component of the digestive system.