Oxygen Transport
(Understanding the BLOOD in blood gases)
If we're going to discuss Arterial Blood Gases, then a few facts about BLOOD seem in order.
Q: Just what makes up BLOOD anyway?
A: Blood has only 3 basic ingredients:
1) RED BLOOD CELLS (RBC's) - you need to understand RBC's to understand oxygen transport.
2) SERUM - this liquid part of the blood contains electrolytes, sugar, proteins, fats, etc. You need to understand serum to understand acid-base.
3) WHITE BLOOD CELLS (WBC'S & Platelets) - forget this, you don't need it to understand blood gases.
When a sample of blood is centrifuged, or just settles by gravity, it looks like this:
CAUTION: What follows are not just some basic facts. They are the basic facts needed to understand blood gases.
Q: Okay, if red blood cells are so important, what exactly is a red blood cell?
A: A red blood cell (RBC) is a tiny human cell found only in the blood stream . It's shaped like a ball that's been flattened on both sides and then dented in. This gives it the most surface area for its size and that's essential for its function.
Oh, red blood cells also make blood - you guessed it – RED!
Q: What's the purpose of a RBC (red blood cell)?
A: The ONLY purpose of a red blood cell is to carry oxygen. RBC's pick up oxygen (O2) in the lungs and transport it to the tissues - kind of like an oxygen delivery truck.
TRIVIA: In fact, red blood cells are so dedicated to oxygen transport, they don't even have a nucleus so they can't even reproduce. Now that's dedication!
Q: So red blood cells transport oxygen, but exactly how do they do that?
A. These pictures are the answer to red blood cell oxygen transport:
A
B
Q: What's the main difference between truck A and truck B?
A: Both trucks are made of iron (in the metal compound known as steel). The difference between A and B is RUST!
Q: Then what exactly is RUST?
A: Rust is simply iron combined with oxygen. (Sorry, but we need a formula here)
Fe + O = FeO
Iron + Oxygen = Iron oxide (RUST)
Q: Iron rusts and trucks rust but do RBC's really RUST carrying oxygen?
A: Yes, but with one key difference. Unlike trucks, red cell rusting is REVERSIBLE. In fact, the iron in the red cell "rusts" (oxidizes) every time it enters the lung. It then "unrusts" (reduces) every time it enters the tissues. This allows pick up and drop off of oxygen.
Q: Why is REVERSIBLE rusting so important?
A: Suppose you order a truck to carry heating oil to your home. The truck fills up at the refinery, drives to your home, pulls into your driveway, turns around, and carries the fuel back to the refinery. Result: Unhappy, cold, blue homeowner.
Now suppose red cells drove up to your lungs, rusted to pick up oxygen, went to your toes, DID NOT release their oxygen, then flowed back to the lungs. Result: Unhappy, blue toes.
Q: Is there actually iron metal that rusts inside the red blood cell?
A: No, red cell IRON is not in its metallic form. Instead, the iron is in a complex molecule called HEMOGLOBIN (heem - o - GLO - bin). When these hemoglobin molecules meet oxygen in the lungs, their iron rusts (oxidizes) and turns red.