1. Respiratory system: The respiratory system brings oxygen into the body and expels carbon dioxide. The lungs are the main organs of the respiratory system, and they work by inhaling air and then exhaling it. The oxygen in the air is absorbed into the bloodstream through the lungs.

2. Cardiovascular system: The cardiovascular system pumps oxygenated blood around the body. The heart is the main organ of the cardiovascular system, and it works by pumping blood through the blood vessels. The oxygen-rich blood is pumped from the heart to the arteries, which carry it to the tissues and organs.

3. Hematopoietic system: The hematopoietic system produces red blood cells. Red blood cells are specialized cells that carry oxygen from the lungs to the tissues and organs. They also contain a protein called hemoglobin, which binds to oxygen molecules and helps to transport them through the bloodstream.

4. Musculoskeletal system: The musculoskeletal system provides support and movement for the body. The muscles work by contracting and relaxing, which moves the bones and other body parts. This movement helps to circulate the blood and bring oxygen to the tissues and organs.