What is the primary role of the anus within the digestive system?

The primary role of the anus within the digestive system is to release waste from the body. This structure serves as the final part of the gastrointestinal tract, where undigested food and waste products, known as feces, are expelled. The anus is equipped with sphincter muscles that control the passage of these waste materials, allowing the body to eliminate substances that are no longer needed after digestion has occurred.

Other options describe functions that are associated with different parts of the digestive system or processes not directly related to the anus. For instance, nutrient absorption primarily takes place in the small intestine, and filtering waste from the blood is a key function of the kidneys rather than the anus. Churning food into a liquid mixture is a function more accurately attributed to the stomach. Therefore, the anus plays a specific and crucial role in the expulsion of waste, marking the end of the digestive process.