Click in the following website and learn how the circulatory system works.
English: http://agrega2.red.es//repositorio/25012010/4d/es_2007073163_0240200/index.html
Spanish:http://repositorio.educa.jccm.es/portal/odes/conocimiento_del_medio/el_aparato_circulatorio_humano/contenido/index.html
