What about bones, cartilage, tendons, and ligaments for structural support? And then there's the central nervous system, which includes sensory inputs (touch, hearing/balance, sight) to make everything run. And what about the endocrine system (pituitary, adrenals, and the like) to give chemical signals during stress? Of course, one cannot neglect the renal part of the circulatory system, else blood volume and composition would be imbalanced. Speaking of blood composition, what about toxin filtering? So there's the liver … but, it also accomplishes glycogenesis, needed for blood energy. And speaking of digestion, what about the large intestine for water absorption and the small intestine for nutrient absorption?

Wow. What a complicated and elegant design!