Final answer:
Oxygen enters the circulatory system 4) continuously throughout the entire respiration cycle.
Step-by-step explanation:
The respiratory process involves both inspiration and expiration, and oxygen continuously enters the circulatory system throughout the entire respiration cycle. During inspiration, the diaphragm contracts and the ribcage expands, creating a pressure gradient that allows air to flow into the lungs.
Oxygen is then exchanged with carbon dioxide in the lungs, and during expiration, the reverse process occurs as air is expelled, ensuring a constant supply of oxygen to the circulatory system. This continuous exchange of gases ensures that oxygen is available for transport to the body's tissues and organs.
The gas exchange occurs in the alveoli of the lungs, where oxygen diffuses from the air sacs into the bloodstream, binding to hemoglobin in red blood cells. Simultaneously, carbon dioxide, a waste product of cellular respiration, diffuses from the blood into the alveoli to be expelled during expiration. This gas exchange is essential for maintaining the proper balance of oxygen and carbon dioxide in the bloodstream and supporting cellular functions.
In summary, 4)oxygen enters the circulatory system continuously throughout the entire respiration cycle, involving both inspiration and expiration. This dynamic process ensures a constant supply of oxygen for cellular metabolism and energy production, highlighting the intricate interplay between the respiratory and circulatory systems.