Comprehensive Biology and Human Body Systems Practice Test 2026 - Free Student Practice Questions and Study Guide

The small intestine is the primary site for nutrient absorption into the bloodstream due to its specialized structure, which includes villi and microvilli that increase the surface area available for absorption. The inner lining of the small intestine has numerous folds, along with these tiny projections, allowing for a more efficient uptake of nutrients such as carbohydrates, proteins, fats, vitamins, and minerals as they are digested.

The small intestine functions after the stomach, where food is mixed with digestive enzymes and acids. As the chyme enters the small intestine, it undergoes further digestion with the help of bile and pancreatic enzymes. The nutrients then pass through the intestinal walls into the blood vessels that transport them throughout the body, whereas the other organs involved, such as the liver and large intestine, play different roles in metabolism and waste processing rather than direct absorption. The gallbladder primarily stores bile to aid in fat digestion but does not directly absorb nutrients.