Why is the ileum long and narrow?

The ileum is long and narrow to maximize the surface area for absorption of nutrients in the small intestine. Its extended length allows for more time to absorb nutrients as chyme passes through, while the narrow diameter helps facilitate the movement and mixing of contents. Additionally, the structure aids in the efficient absorption of bile salts and vitamin B12, which are crucial for digestion and overall health. This design is essential for the effective function of the digestive system.