What Is Blood Anyway?

A few years ago I had a great opportunity to write an article series for EMS Magazine called Blood On Tap. It was all about the pioneering work being done by different pharmaceutical groups to create artificial substitutes for blood.

The technical name for the pharmaceutical products that mimic the properties of blood is “oxygen therapeutics.” Here’s the inside scoop, directly from the drug company big wigs, on why we don’t call them something cool like artificial blood.

The thing is, the drug company’s know full well that these fancy solutions are nowhere near advanced enough to mimic the many complex properties and functions of blood. That’s why they are aiming for the single goal of reproducing bloods ability to carry oxygen around the body. And, hence, the more lame name.

All told, blood is pretty magical stuff. Our understanding of blood in the prehospital universe only scratches the surface of all of bloods capabilities. However, there are several functions and properties of blood that you should know.

Here’s a quick crash course:


Plasma is the viscous, pale yellow fluid that all of the products of blood are dissolved or suspended within. If you’ve ever seen a blood tube after it’s been spun in a centrifuge, plasma is that thin yellow band of goo that form at the top. While plasma is 90 percent water, it remains pretty amazing.

Proteins, platelets, electrolytes, dissolved gasses and nutrients are all suspended within the plasma fluid. Waste products are also transported within plasma to the liver, kidneys and lungs for disposal. Dissolved within that thin yellow band are everything needed to form and dissolve clots, fight infections, maintain acid / base balance, feed the cells and maintain osmotic pressures.

Plasma also collects in lymph nodes and is the precursor to lymph.

Red Blood Cells (Erythrocytes)

These little beauties are our oxygen transport system. Unlike CO2, oxygen doesn’t dissolve readily into blood. Only 2% of all the body’s transported oxygen is dissolved. The rest of it takes a ride on a red blood cell.

How much oxygen gets transported you ask? Good question. At rest, the human body consumes about 4ml of O2 per kilogram of body weight each minute. 98% of that O2 takes a ride on the complex protein molecules known as hemoglobin, inside each red blood cell.

If you’re ever discussing hemoglobin at the dinner table (it comes up), you can make you friends think you’re smarter than you really are by mentioning that each hemoglobin molecule can only bind with four oxygen molecules at a time. So if you could measure the oxygen saturation of a single hemoglobin molecule, there would only be five possible outcomes, 100%, 75%, 50%, 25% and 0%.

As an additional side note, I’ve built a career out of making people think I’m smarter than I am.

White Blood Cells (Leukocytes)

These guys are always present in the blood stream, traveling around looking for foreign invaders like bacteria, viruses, fungi other unnaturalized citizens of the human body. Most leukocytes don’t float freely in the bloodstream. they remain bonded to the vascular wall and only move when they receive a chemical signal that they are needed to fight an infection.

When the physical environment is stable most of us have between 5,000 and 9,000 White Blood Cells. That number increases in the presence of infection, stress, injury, exertion, seizure and some drugs. Increased white blood cell counts in a hallmark sign of infection and in more severe cases the number of leukocytes can jump to 16,000.

Platelets (Thrombocytes)

Large cells known as megakaryocytes produced within the bone marrow break apart to create platelets. Platelets are responsible for our bloods ability to clot. When platelets contact damaged tissue, they bind to that tissue and release an enzyme that causes their surface to become sticky. Other platelets then aggregate or stick together and form a plug. Platelets also release chemical messengers that create a “clotting cascade” binding the platelets together.

A patient with to few platelets (thrombocytopenia) may be at increased risk for blood loss due to an inhibited ability to clot and stop bleeding. The condition of having to many platelets, (thrombocytosis) may lead to abnormal clotting in blood vessels and conditions like deep vein thrombosis, pulmonary embolism, heart attack or stroke.

Platelets have a seven to ten day life span and are eleminated by the spleen.

Crash course complete. See you next time.



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