Which of the following is not a function of the digestive system?

The digestive system primarily functions to process food to extract and absorb nutrients, break down food into smaller components, and eliminate waste products from the body. Each of these functions is critically linked to the overall process of digestion and nutrient absorption.

Regulating blood sugar levels, however, is not a direct function of the digestive system. Instead, this regulation is primarily the responsibility of the endocrine system, particularly through hormones such as insulin and glucagon produced by the pancreas. While digestion impacts the availability of glucose and other nutrients in the bloodstream, it is the hormonal response that controls and maintains blood sugar levels after nutrients have been absorbed. Hence, this option is distinct from the core functions of the digestive system.