The level of oxygen in the blood...
the level of carbon dioxide in the blood...
the level of oxygen in the alveoli...
the shape of the alveoli...
the shape of the lungs....
Body planes, look at this website for more info
https://www.google.co.uk/url?q=https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/introduction-to-anatomy-and-physiology-1/mapping-the-body-33/body-planes-and-sections-289-1344/&sa=U&ved=0ahUKEwjQs8XR9YrUAhXHKcAKHapnD58QFggUMAI&usg=AFQjCNH0hXmL_w50JNtIeUTU7BDPw10XDg