2026 Complete Practice Test for Senses, Endocrine, Blood, Heart, and Reproductive System

Digestion and absorption occur primarily in the small intestine. After chyme leaves the stomach, pancreatic enzymes and bile mix in the small intestine to break down carbohydrates, proteins, and fats. The inner lining has villi and microvilli that dramatically increase surface area, allowing nutrients to be absorbed efficiently into the bloodstream or lymphatic system. This combination of ongoing digestion and extensive nutrient absorption is what makes the small intestine the main site for these processes. For context, storing and concentrating urine is a function of the urinary system, the reservoir for bile is the gallbladder, and filtering blood plasma is a kidney function.