The gastrointestinal tract is a complex biological system comprising the alimentary canal, a continuous tube that extends from the mouth to the anus. Its primary function is the digestion and absorption of nutrients from ingested food. The process begins with mechanical and chemical breakdown in the mouth and continues through the esophagus, stomach, small intestine, and large intestine. Digestive enzymes, bile, and acids act upon macromolecules, breaking them into absorbable units. The small intestine is the principal site of nutrient absorption, where monosaccharides, amino acids, and fatty acids pass into the circulatory and lymphatic systems. Undigested material and water are processed in the large intestine, forming feces, which are then eliminated from the body.