USMC Force Fitness Instructor Course (FFIC) Practice Test 2025 - Free FFIC Practice Questions and Study Guide

The urinary system plays a critical role in maintaining homeostasis within the body by excreting toxins and regulating electrolyte levels. This system is responsible for filtering blood, eliminating waste products through urine, and balancing electrolytes, which are essential for various bodily functions including nerve transmission, muscle contraction, and hydration. By removing excess sodium, potassium, and other electrolytes, the urinary system ensures that the body remains in equilibrium, preventing conditions such as dehydration or overhydration, and keeping the internal environment stable.

The other options relate to different systems in the body. Producing digestive enzymes pertains to the digestive system, while churning food in the stomach is also a function of the digestive system. Absorbing nutrients from food specifically involves the intestines, which is another aspect of the digestive system. Therefore, B is the most relevant to the function of the urinary system.