I need help creating a thesis and an outline on Gas Exchange and Transport. Prepare this assignment according to the guidelines found in the APA Style Guide. An abstract is required. When breathing out, as in figure 2, external intercostals relax, moving the sternum and ribs inwards and outwards and reduce chest width. At the same time, the diaphragm relaxes and ascends, reducing chest depth. The thoracic capacity is reduced and inter-pleural pressure increases, causing the elastic lung tissue to recoil (LeVert, 2012: p22). This increases air pressure in the alveoli above atmospheric pressure, leading to air in the alveoli being forced out into the atmosphere.

Both lungs have ~300 alveoli each, which expands when air enters the lungs through the bronchi and bronchioles. Blood-filled capillaries surround these alveoli. Both the alveoli and the capillaries have one-cell thick membranes, which makes for a thin blood-air barrier between the interior of the alveoli and the blood (Fishman et al, 2011: p39). Thus, oxygen easily diffuses into the blood. Carbon dioxide produced by the body as a waste product is also transported by the blood to the lung capillaries, where it flows into the alveoli by diffusion without facilitation. In this case, oxygen molecules are at a higher concentration in the alveoli compared to the lungs, while CO2 is at a higher concentration in the blood compared to the alveoli (Fishman et al, 2011: p39). This enables the flow of oxygen in inhaled air into the blood, while carbon dioxide in the blood flows into the alveoli.

As shown in figure 3, the activity of the external intercostal muscles, diaphragm, and respiratory muscles is regulated through nerve impulse transmission from the brain, specifically through the intercostal and phrenic nerves (Honda, 2012: p43). Respiratory depth and rhythm are essentially controlled in the pons and the medulla. Whereas the medulla sets the breathing rhythm through the self-exciting inspiratory center, the pons centers smooth out these basic expiration and inspiration rhythms. It is these impulses between the medulla and the pons centers that maintain the human respiration rate per minute, which are ~12-15 inhalations/expirations. When one is engaged in a demanding physical activity, the brain respiration centers increase the rate of impulses sent to the muscles of respiration, enabling deeper and more vigorous breathing, in a process referred to as hyperpnea (Dempsey & Pack, 2011: p60). Still, physical activity does not always result in an increase in the breathing rate.