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.