All About Blood

Blood is quite important and permeates nearly every part of our internal body.  It is connected to many different aspects of our daily life: our diet, our general health, and many diseases.  Look for an upcoming post on information gleaned from blood.  For now though, read on for some basic facts of blood.  As an added bonus, learn blood stories of historical significance of George Washington, Rasputin, and Lance Armstrong.

What is Blood?

Blood is considered a connective tissue, which categorizes it with fat, bones, muscles, and ligaments.  Blood consists of 55% plasma, and the majority of the plasma is made up of water.  The remaining 45% of the blood is made up of hormones, waste products, mineral ions, proteins, and a variety of blood cells.  In the blood cell category, there are red blood cells, white blood cells, and platelets.  Red blood cells are the most numerous and give blood its red color.  White blood cells are crucial to your immune response, and platelets help clot your blood.  Red blood cells carry oxygen to tissues of the body.  Contrary to popular science charts and the color of surface veins seen through your skin, deoxygenated blood found in the veins is not blue, rather it is a darker red.   Veins look blue through your skin due to the light scattering properties of the layers of skin.  Blue wavelengths penetrate further into the skin layers than red wavelengths, giving the veins their blue hue.

Venous blood (darker) and arterial blood (brighter) / Photo by Wesalius and available CC BY-SA 3.0

Blood Functions

Blood is the transport system throughout your body.  It brings oxygen, hormones, and other nutrients to the cells of your body.  Blood removes waste products from your cells taking them to the kidneys and liver.  It also helps with thermoregulation.  When you are hot, the body forces more blood to the surface of your body to help cool your body down.  When you are cold, the body reduces blood flow to the extremities to help keep your organs warm and functioning.  One obvious effect of this is that frostbite commonly occurring on the toes and fingertips but not on your torso.   

Blood Clotting

When a blood vessel gets injured, the blood comes in contact with substances in the vessel walls and the skin that it normally would not come in contact with.  This contact triggers mobilization of the platelets, which are irregularly shaped cells that stick to the edge of an injured blood vessel and to each other.  Platelets also chemically signal to each other to recruit more platelets.  They change shapes to plug the holes where the blood is rushing out.  Platelet action also signals proteins called “clotting factors” which link up and form long strands called “fibrin.”  The fibrin get tangled in the net of platelets (imagine long hair on a shower drain) and create a stronger more solid clot.  As the damaged tissue heals, the clot slowly resorbs.

Scanning electron microscope image of a red blood cell (left), a platelet (middle), and a white blood cell (right) / Image available in the public domain

Too much clotting can be a bad thing.  Clots can float through the arteries and get caught and tangled in the capillaries in your brain, which can cause stroke.  They can also get caught in your lungs, causing a pulmonary embolism.  Or they can get caught in various places on your body, causing deep vein thrombosis, or DVT.  Plaque breaking off the walls of your artery can initiate the clotting response, which can lead to a heart attack.  Blood thinners can be administered to help with the dissolution of the clots.

Conversely, without clotting, the body would bleed out.  There are several disorders involving lack of clotting.  A notable historic case of clotting disorders would be the hemophilia of Alexei Nikolaevich, Tsarevich of Russia in the early 1900s.  Alexei’s hemophilia, and the resultant reliance on the Russian faith healer and mystic, Rasputin, helped to contribute to the end of the Romanov Dynasty with the February Revolution in 1917.  Rasputin was initially called in to help heal Alexei (which, in all actuality, he couldn’t with the medical knowledge of the time).  Alexei’s hemophilia was a closely guarded secret, as he was heir to the throne, and the people of Russia couldn’t understand the royal family’s relationship with the well-hated Siberian peasant.  This, combined with the withdrawal of the family from society to hide the hemophilia, created suspicion of the Russian aristocracy.  Additionally, World War 1 showed the ineffective leadership of the Tsar in both the political and military realm and there were food shortages and high food prices.  These contributing factors, and more, resulted in the arrest of the royal family.  They were exiled in Siberia and then executed in 1918.  Hemophilia now, thought, is not considered an executable offense–modern medicine has a variety of procedures and medicine to help current sufferers of hemophilia and similar diseases.

Alexei Nikolaevich, Tsarevich of Russia 1904-1918 / Image available in the public domain

Volume of Blood

Humans typically contain approximately 5 liters of blood, about 1.3 gallons.  Men have slightly more blood than women.  Newborn babies are born with about a cup of blood.  Children have about as much blood as adults by the age of 5 or 6 [1].  

Losing blood in large amounts can send the body into shock, and can be fatal.  This is called hypovolemic shock or hemorrhagic shock and can set in at about 20% blood loss.  George Washington, on a fateful day about two and a half years into his retirement (Dec 14, 1799), developed a sore throat and couldn’t breathe.  Doctors were called in and let out his blood in hopes of reducing the inflammation in his throat.  Over 12 hours, about 2 liters–40% of his blood–was let out.  Additionally, the doctors applied Spanish fly to his throat (resulting in terrible blisters), and administered vomit inducing drugs and enemas.  These procedures were common and in alignment with the Hippocratic medicine practiced during that time.  If the actual disease didn’t kill George Washington, the doctors certainly did [2].  

At higher altitudes, the body creates more red blood cells to adjust for the lack of oxygen in the air.   People living at higher altitudes can have up to 30-50% more red blood cells in their body [3].  The added red blood cells provides an obvious advantage to athletes training at higher altitudes and racing at sea level, as they have more red blood cells to carry oxygen during the event.  Athletes have realized this and many live and train at high altitudes for this purpose.  Some companies even have designed “sleep tents” which allow the users to sleep in an environment that mimics the air at high altitude (here is an example).  This allows the athlete to take advantage of high altitude air (more red blood cells) while training at a lower altitude which also has advantages (avoiding immunosuppression, muscle loss, excessive dehydration, and fatigue common to training at high altitudes).

High altitudes increase red blood cells counts by 30-50% / Photo by Karl Trellinger

Blood Doping

Some athletes avoid the hassle of training at altitude and sleep tents and just blood dope, or blood dope in addition to altitude training.  Blood doping involves artificially inflating the oxygen carrying capacity of the blood.  Lance Armstrong made EPO and blood doping household terms.  EPO is short for erythropoietin, which is a hormone produced by the kidneys that stimulates red blood cell production.  Athletes will inject EPO creating an artificial rise in the manufacture of red blood cells.  

Lace Armstrong, doper / Photo available in the public domain

Blood transfusions also fall in the category of blood doping.  In this case, the athlete “donates” blood, which is then spun, the red blood cells extracted and stored, and the remaining blood components returned to the athlete.  Then, shortly before a competition, the previously extracted red blood cells are returned to the body.  The athlete will have more red blood cells during the competition than normal, leading to enhanced performance.  Sometimes the athlete uses blood donated by someone else so as to not interfere with the training regimen leading up to the race.  

Another popular blood doping tactic is using synthetic oxygen carriers which are not red blood cells.  The proteins or chemicals (depending on which carrier you use) helps deliver oxygen to the body by riding through the circulatory system, as a red blood cell would.  

The side effects of blood doping are sluggish blood and increased clotting risk.  Clotting blood can lead to pulmonary embolisms, strokes, heart attacks, and death.  Blood doping is banned by the World Anti-Doping Agency.  

Donating Blood

Blood is often transfused to patients that have undergone a traumatic injury or are low on blood due to cancer treatments, blood diseases, or surgery.  The blood comes from donations.  In order to donate blood, the donor has to be in good health and not have been exposed to blood transmitted diseases.  The actual blood donation process takes about 10 minutes.  The donated blood is then tested further for diseases like hepatitis, HIV, and syphilis.

About a pint of whole blood, obtained from a volunteer donor / Photo available in the public domain

After donation, whole blood is sometimes separated into red blood cells, plasma, and platelets.  Platelets have a shelf life of 5 days, red blood cells about 42 days, and plasma lasts about a year.  About 5% of the blood is discarded due to contamination or expiration.  Donated blood is then sold to hospitals, but not necessarily locally.  I found quotes ranging from $100-600 for a pint of red blood cells [4] [5].  The money obtained from selling the blood is used to cover the costs of collection and testing.  Blood on the coast costs more than from the heartland of the country, as labor and rent needed for collecting the blood cost more on the coasts.  

Until the 1970s, a large portion of the nation’s blood came from paid donors.  However, a government study found that paid donors had a much higher rate of hepatitis in the blood, resulting in the USA switching to only using donated blood.  Theoretically, you could still be paid to donate blood, but no establishment will buy it because of the higher chance for hepatitis.  Plasma donation still uses paid donors.  The plasma from paid donors is typically purchased by pharmaceutical companies [6] and is broken down into many products to become pharmaceuticals, so the risk of disease transmission is low.  Fun fact: the USA is the world’s leading supplier of plasma, producing 60% of the world’s annual yield [5].  

My Conclusions

Blood is critical for life as we know it.  Most of us take it for granted until a medical issue arises.  Donate blood if you are feeling altruistic and unconcerned the post-donation blood market.  Most importantly, don’t dope!


[1] Geggel, Laura. “How Much Blood Is in the Human Body?” LiveScience. Purch, 03 Mar. 2016. Web. 26 Mar. 2017.

[2] Markel, Howard. “Bloodletting, Blisters and the Mystery of George Washington’s Death.” Interview by Jeffrey Brown. PBS. Public Broadcasting Service, 15 Dec. 2014. Web. 27 Mar. 2017.

[3] Braverman, Jody. “How to Train for High Altitude Hiking.” LIVESTRONG.COM. Leaf Group, 03 July 2015. Web. 27 Mar. 2017.

[4] LaGrone, Katie. “Blood Money: What You Didn’t Know about Your Blood Donation.” WPTV. The E.W. Scripps Co, 04 Nov. 2013. Web. 27 Mar. 2017.

[5] Berry, Kathleen M. “All About/Blood Banks; A Multibillion-Dollar Business in a Nonprofit World.” The New York Times. The New York Times Company, 06 July 1991. Web. 27 Mar. 2017.

[6] Engber, Daniel. “Does the Red Cross Sell Blood?” Slate Magazine. The Slate Group, 11 Sept. 2006. Web. 27 Mar. 2017.

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