Atelectasis is composed of 78% nitrogen and 21% oxygen. Since oxygen is exchanged at the alveoli-capillary membrane, nitrogen is a major component for the alveoli's state of inflation. If a large volume of nitrogen in the lungs is replaced with oxygen, the oxygen may subsequently be absorbed into the blood, reducing the volume of the alveoli, resulting in a form of alveolar collapse known as absorption atelectasis. It is usually associated with accumulation of blood, fluid, or air within the pleural cavity, which mechanically collapses the lung. This is a frequent occurrence with pleural effusion, caused by congestive heart failure (CHF).
Neoteny in humans body is indicated by glabrousness (hairless body). Neoteny of the genitals is marked by the absence of a baculum (penis bone); the presence of a hymen; and the forward-facing vagina. Neoteny in humans is further indicated by the limbs and body posture, with the limbs proportionately short compared to torso length; longer leg than arm length; the structure of the foot; and the upright stance. Humans also retain a plasticity of behavior that is generally found among animals only in the young. The emphasis on learned, rather than inherited, behavior requires the human brain to remain receptive much longer. These