structure of alveoli tiny air sacs enabling gas exchange in the lungs

white background scientific design detailed co2 educational circulation healthy tissue drawing capillary bronchiole cell red vector graphic biology artery science vessels care breath organ dioxide carbon gas lungs human oxygen blood structure exchange medical anatomy alveolus respiration air respiratory alveoli health pulmonary medicine bronchi diagram lung system tiny sacs enabling balloon-like thin walls surrounded capillaries font circle line text brand cartoon presentation logo pattern eye advertising nose document poster