This lecture offers a detailed explanation of the journey of food through the digestive system, highlighting the processes of mechanical digestion in the mouth, acidic breakdown in the stomach, and the critical role of the small intestine in digestion and absorption. It emphasizes the significance of the small intestine's structure, including villi and microvilli, for maximizing surface area and the presence of brush border enzymes for final nutrient breakdown. The lecture also covers the absorption mechanisms for carbohydrates, proteins, and fats, noting the reliance on sodium for sugar and amino acid transport, and the unique path of fat absorption through the lymphatic system with the help of bile salts. Finally, it touches upon the functions of the large intestine in water absorption and the importance of the gut microbiome for vitamin synthesis and protection against pathogens.