<span>nebula--------» Protostar----------» Main Sequence----------» Red Giant---------»White Dwarf</span>
#1 is CO2 exchange. CO2 is diffusing from the blood into the alveoli for expiration.
#2 is O2 exchange. O2 is diffusing from the alveoli into the blood to be carried to the tissues.
The circulatory and respiratory systems work together to circulate blood and oxygen throughout the body. Air moves in and out of the lungs through the trachea, bronchi, and bronchioles. Blood moves in and out of the lungs through the pulmonary arteries and veins that connect to the heart.
