Which term describes the act of inhaling into the lungs?

Inhaling into the lungs is specifically referred to as inspiration. This term describes the process of drawing air into the lungs, which is a crucial part of the respiratory cycle. During inspiration, the diaphragm and intercostal muscles contract, expanding the thoracic cavity and decreasing internal pressure, allowing external air to flow in.

Respiration generally encompasses both the process of inhaling (inspiration) and exhaling (expiration), thus it is a broader term that includes both phases of the breathing cycle. Expiration refers to the act of exhaling air out of the lungs and does not describe the act of inhaling. Excretion is related to the elimination of waste products from the body and is not directly related to the process of breathing. Therefore, the choice of inspiration accurately identifies the specific action of inhaling air into the lungs.