The organ in the human body primarily responsible for digestion is the stomach. The stomach is a muscular, hollow organ that plays a crucial role in breaking down food after it is ingested. It secretes digestive juices, including hydrochloric acid and digestive enzymes, which help to chemically digest food and facilitate absorption in the small intestine. The stomach also churns food, mixing it with these juices to form a semi-liquid substance known as chyme. This process is critical for the overall digestion and absorption of nutrients, ensuring the body receives the necessary elements for energy and growth.