Hint: The lungs are the center of the respiratory (breathing) system. Every cell in the body needs oxygen to maintain life and health. Your body also needs to remove carbon dioxide. These gases are waste products produced by cells in normal daily work.
The places where breathing gas actually diffuses are the alveoli and capillaries.
Alveoli: Alveoli are hollow cup-shaped cavities where gas exchange occurs in the lung parenchyma. Alveoli are found in acne at the beginning of the breathing zone. They are sparsely located in the respiratory bronchioles, arranged on the walls of the alveolar ducts, and are more abundant in the alveolar sacs at the blind end. The acinar is the basic unit of breathing, and gas exchange occurs in all the existing alveoli.
The alveolar membrane is the gas exchange surface and is surrounded by a network of capillaries. The oxygen on the entire membrane diffuses into the capillaries, and carbon dioxide is released from the capillaries to the alveoli to be exhaled. Alveoli are specific to the lungs of mammals. Gas exchange in other vertebrates involves different structures.
Capillaries: A capillary is a small blood vessel with a diameter of 5 to 10 micrometers, and its wall thickness is an endothelial cell. They are the smallest blood vessels in the body: they carry blood between small arterioles and venules. These capillaries are places where many substances exchange with the tissue fluid surrounding them.
Note: Oxygen only plays a small role in breathing. The air we breathe contains 21 percentages of oxygen, while our body consumes only 5percentages of oxygen, and the rest is exhaled. The lung is the only organ that can float on water.