In mammals, the process of inspiration involves:

The process of inspiration in mammals primarily involves decreased pressure generated within the chest cavity. When mammals inhale, the diaphragm contracts and moves downward while the intercostal muscles between the ribs expand the rib cage. This expansion increases the volume of the thoracic cavity, which causes the pressure inside the chest to drop below atmospheric pressure. As a result, air is drawn into the lungs to equalize the pressure difference.

During inspiration, the decrease in pressure allows air to flow into the lungs more effectively, facilitating gas exchange. This mechanical principle is rooted in Boyle's Law, which states that a decrease in pressure within a closed space will lead to an influx of air from areas of higher pressure (in this case, the outside atmosphere).

Other options do not accurately describe the process of inspiration. For instance, increased pressure in the chest would hinder air intake, while a flat diaphragm and relaxed intercostal muscles would be associated with expiration rather than inspiration. Lastly, while increased oxygen levels may occur in the bloodstream as a result of the breathing process, this is not a direct mechanism of the act of inhalation itself. The focus during inspiration is on creating negative pressure in the thoracic cavity to facilitate airflow into the lungs.