Respiratory-Circulatory

The circulatory system and the respiratory are like one big team in the human body. The respiratory system inhales many different molecules in the air, the most important molecule is oxygen. That oxygen is delivered to the air sacs called, alveoli. The alveoli have very thin walls and are surrounded by capillaries. The thin walls of the alveoli allow the oxygen to diffuse into the capillaries and onto some hemoglobin on the red blood cells that have been de-oxygenated (blue color). The red blood cells are now oxygenated turning a red color and return through the pulmonary vein and pumped to the rest of the body in arteries delivering to the cells. The respiratory system also gets rid of Co2 created by cell respiration. The Co2 diffuses out of the cells into veins towards the vena cavas and out the pulmonary artery. From there, the pulmonary artery takes the co2 and de-oxygenated blood out to the capillaries and take a gas exchange ending in the alveoli. Once the person breathes out, the Co2 gets exhaled out of the body.
For more information about the relationships- http://www.ehow.com/about_5465406_do-cardiovascular-system-work-together.html