Journey around the Earth Two and a Half Times
Around the World in Eighty Days is a novel by Jules Verne, published in 1873. In the story, Phileas Fogg, a gentleman from London, wagers £20,000 on whether or not it is possible to circumnavigate the world in eighty days. To win the wager, he and his valet Passepartout leave for a long eighty-day journey, starting from London to India, Japan, and the U.S., and back to London.
However, what is amazing is that a journey over twice longer than the round-the-world journey from the story is going on in our body. The one that makes this fascinating journey is blood.
Blood is made in the bone marrow. Blood consists of plasma that is mainly water, and of blood cells. The total weight of the blood that travels our body is about 7–8% of body weight. For example, if a man weighs 60 kg [132 lbs], he would have around 5 ℓ [1.3 gal] of blood. Those 5 ℓ of blood constantly moves around the body through the vessels, transporting oxygen, carbon dioxide, nutrients, and waste.
Then why is blood red? Blood is red because of the red blood cells which take up most of the blood cells. There are about 25 trillion red blood cells in the human body. These red blood cells are shaped like biconcave discs (flattened disk with depressed centers), and have a diameter of about 7.5 µm. These tiny red blood cells play a very important role to receive oxygen from the lungs, transport it to cells, and receive carbon dioxide from cells and transport it to the lungs.
Red blood cells have protein called hemoglobin, which contains iron that binds oxygen. Just like rusted iron is red, the iron in hemoglobin is red when combined with oxygen. What is more amazing is that each tiny red blood cell contains about 250 million hemoglobin molecules. And one red blood cell can carry about 1 billion oxygen molecules.
Inside the blood, there are other travelers as well as the red blood cells. Among them, the white blood cells, which are clear, protect the body against foreign invaders. When a germ or a foreign substance comes inside the body, the white blood cells produce antibodies to fight against them, and incapacitate the invaders. They also directly attack the foreign substances that come inside the body and swallow them.
Platelets, which are the tiniest and randomly shaped blood cells, form clots to stop bleeding. When the blood vessels get damaged and your skin or mucous membranes start bleeding, blood will continue to flow out and it needs to be stopped. When this happens, the platelets clump together and clot blood vessel injuries to stop blood from coming out of the body. This process of coagulation starts as platelets throw themselves to burst.
While we are letting the day pass by without feeling their existences, about 200 billion red blood cells, 100 billion white blood cells, and 200 billion platelets are newly formed, and carry out their duties silently. The red blood cells leave the heart, deliver oxygen to cells, and come back to the heart within 23 seconds of their departure. The red blood cells live about 120 days, and about 1 out of 125 of them are replaced with the new ones every day. As for the white blood cells, it depends on the type, but many of them don’t last longer than a few hours; each of them destroys about 5 to 50 germs and dies. As for platelets, they live up to 10 days if they last long. About 15% of the blood in our body is extra blood, and blood is easily filled with newly formed platelets, which is why we can keep our health without any problems even though we donate blood.
With what force can blood travel around the whole body? The heart’s regular pumping is the driving force of the blood circulation. The powerful force that circulates the blood from the head to toe comes from the special heart muscle. When we run, we can feel the heart is beating. However, we cannot stop the heart from beating at our will like how we can bend or stretch out. In the heart which is controlled by the autonomic nerve system, there are special cells called sinoatrial node1) which periodically produces an electrical impulse autonomously. By the electrical impulse of the sinoatrial node, the heart starts beating and is adjusted, which is why the sinoatrial node is called the pacemaker.
1) Sinoatrial node: a small body in the heart, which produces an electrical impulse, causing the heart to contract and setting the rhythm of the heart.
Normally, your heart is slightly larger than your fist. It beats 72 times a minute, and about 100,000 times a day, and about 2.9 billion times without stopping by the age of 80. If the arm or the leg muscles try to move as much as the heart does, they will get tired as soon as they start moving. However, the heart doesn’t get tired even after beating billions of times. When the left ventricle beats once, it sends out about 70 ㎖ [2.4 oz] of blood to the whole body through the arteries, which means that a heart pumps a tremendous amount of blood, that is, 300 ℓ [79 gal] per hour, and about 7,000 ℓ [1,850 gal] per day.
Blood travels through the blood vessels with the help of the heart, carrying a significant duty. Arteries and veins are like highways that go through the main regions of a country; they are thick, and a large amount of blood passes through them. And capillaries which are very thin tubes that reach even the tips of the fingers and toes spread to every corner of our body. However, the journey of the blood isn’t so easy. When it passes through the arteries which are the ways out from the heart, it needs to endure great pressure from the heart, and the capillaries are so thin that they are just big enough for one red blood cell to barely fit through by shrinking its whole body. On the way back to the heart through the veins, the blood manages to come back to the heart with the help of the valves 2).
2) Valve: a valve that exists in the heart and in the veins to prevent backflow of the blood
The blood, which pumps out of the heart and passes through the arteries, provides various parts of the body with oxygen and nutrients and receives carbon dioxide and waste while traveling through the capillaries. Then it comes back to the heart. The blood which gives oxygen to the cells goes back to the lungs to receive oxygen again. When it arrives at the lungs, it hands to the lungs the carbon dioxide, which it received from the cells, and receives oxygen from them, and goes back to the heart where it started its journey. The blood is making this journey even at this moment without resting.
The length of the blood vessels, including the capillaries through which tiny blood cells travel along the blood, is 100,000 km [62,137 mi], which is long enough to travel around the earth two and a half times when they are all connected as one line. It is hard to even imagine that a 100,000 km-long path is densely packed within the human body that is usually less than 2 m [6.5 ft] long. The heart sends out about 5 ℓ [1.3 gal] of blood per minute, and it takes less than a minute for the blood to leave the heart and come back to it. The long journey of the blood is not for anybody else, but for “me” only. For example, the brain needs a large amount of oxygen and glucose, but it can only depend on the blood’s supply of them since it doesn’t have the ability of storing them. That is why a man becomes unconscious when the blood circulation stops even for just 15 seconds, and the brain is damaged to the point it cannot be recovered if the blood circulation stops for only four minutes. When the blood stops circulating even for a few seconds, we can neither see nor hear; we can’t do anything. That’s how important the long journey of the blood is for our body.
We want some very special miracles to happen in our life. However, something special has no meaning without something ordinary. We spend each minute with no problems. Isn’t this a true miracle? The miracle in our daily life is happening even at this moment. It is the journey around the earth two and a half times!
- EBS DocuPrime Blood Part 2, Secret of 8% (Broadcast on Sept. 30, 2009)
- EBS Knowledge Channel Episode 1006, Blood (Broadcast on May 14, 2013)
- Kim Sa-yeol and 4 others, Mystery of Life —Life like River, Academy Books, 1999