Students discover the roles of key body systems and the major organs, cells, and tissues that make them up in this unit. Take a look at the circulatory system and the job of the heart, arteries, veins, capillaries, red blood cells, white blood cells, and platelets. Explore the respiratory system and learn about the nose, lungs, and air sacs. Move into the digestive system and learn about the mouth, esophagus, stomach, small intestine, villi, large intestine, and liver. Also covered are the urina