The red blood cell's journey starts in the bone marrow, where after 7 days of maturation, it is released into the bloodstream. The production of red blood cells is controlled by the kidney releasing a chemical called erythropoietin (EPO), which is triggered by an O2 deficiency in the Kidney.

Once the red blood cell has matured, it can start doing the job it is created for. The red blood cell exists to carry oxygen throughout the bloodstream and body, which it does through hemoglobin; hemoglobin carries oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues back to the lungs. Hemoglobin is a protein found within red blood cells that is crucial to the red blood cell, it can also carry up to 4 oxygen molecules at a time.

Along the way, a red blood cell encounters many other things in the blood. White blood cells, which fight infections, are another crucial part of your body functions. Platelets are present to help clotting if the skin gets cut and one starts bleeding, so that the bleeding eventually stops. Plasma is a yellow-ish liquid responsible for carrying nutrients, hormones, proteins, etc. through the body. Hopefully it won't, but a red blood cell could also encounter blood-borne viruses such as HIV, AIDS, or hepatitis B.

The red blood cell is allowed to make this awesome journey because it is pumped by the heart muscle, which is so powerful that the red blood cell is able to travel all the way around the body. When oxygen depleted blood returns to the heart, it is then pumped to the lungs. After it has been oxygenated in the lungs, it is pumped back to the heart, and from there pumped to the rest of the body.

The lungs are an important part of the red blood cell's journey as well, because that is where red blood cells bring waste CO2 to be exhaled. The lungs are also where hemoglobin binds with oxygen as oxygen molecules enter the lungs.

The red blood cells travel through the body on its journey in veins and arteries. Veins are for blood towards the heart, and arteries are full of blood travelling away from the heart. The heart pumps blood out through the pulminary arteries and in through the vena cavas. Blood goes from the heart to the arteries, arteries to arterioles, and arterioles to capillaries. From the capillaries, the oxygen goes to the interstitial fluid and cells, while the deoxygenaged blood travels through veins and venues back to the heart, where the process restarts. Veins rely on muscle contraction to return blood to the heart, and many veins have valves that ensure blood can only travel one way.

The End.