The body needs proteins, carbohydrates, fats, vitamins and minerals. Vitamins are organic molecules that are needed for chemical reactions. the body cannot produce on its own and must derive it from food. Minerals are inorganic molecules that are needed for many body structures, and also must be taken from food.
The Digestive System
The digestive system is an organ system for the uptake, digestion, and absorption of food. The mouth and trachea are for uptake. The stomach is for storage and digestion. The small intestines are for absorption of nutrients into the blood, and are folded to increase surface area. The large intestines are for absorption of water to concentrate waste. The rectum is for excretion of waste.
The Excretory System
The excretory system is for removing waste from the body. The kidneys filter the blood to decide what the body needs or has too much of. The ureter and bladder are for storage of waste to be excreted as urine.