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Thursday, July 25, 2013

Pallor vs. cyanosis

Anemia's Pallor vs Hypoxemia's Cyanosis

What is the difference between the causes of pallor and cyanosis?

Pallor = Pale
Cyanosis = Blue

Anemia causes Pallor.
Hypoxemia causes Cyanosis.

So what are the differences between the mechanism of Anemia and Hypoxemia?

Think of our blood as a giant River, a RBC as a Ferry, our hemoglobin as red Cars on the ferry, and oxygen as People.

RBC in Blood, represented by Ferry in River
Hemoglobin in RBC, represented by red Cars in the Ferry

Oxygen dissolved in blood, represented by People swimming in River

4 Oxygen bound to 1 Hemoglobin, which is in the RBC,
represented by 4 People in 1 red Car, which is on the Ferry.
What the ferry does is that it transports people from one place to another. (like how our RBC transports oxygen from our Lungs to our Tissues.)

The thing is, the red Cars are always on the ferry, never leaving it. And the ferry is so BIG that it can never go near the river bank, so People have to swim from the river bank onto the Ferry. (like how oxygen first have to get dissolved into blood first then only get into the RBC's Hb)

Once these People get on the Ferry, they instantaneously get into the red Cars, which can only fit 4 People per Car. (4 O2 molecules per hemoglobin)

The amount of People in the red Cars = the amount of Oxygen bound to hemoglobin.
The amount of People swimming in the River = the amount of Oxygen dissolved in the blood.

Cyanosis is seen when the red Cars, which have 4 seats, are not adequately seated with people, hence they are "people-empty".(like how our hemoglobin is not saturated with oxygen)

So what can cause our red Cars to be "people-empty"? Quite a number of things! Here are the examples of the 2 main causes.

Cause 1 : Very little People swimming in the River (low dissolved O2)
This can be due to problems at the River bank (alveolus). This causes less people jumping from the River bank into the River(less oxygen enters blood from alveoli). And therefore, there are less people swimming in the River, which leads to less People being on the Ferry.
There can be many problems which lead to less people jumping from River bank into River, such as people not being able to get to the River bank, or something is barricading the River bank, or there is no blood in the River etc. (these will be covered in a seperate post, stay-tuned!)

Cause 2 : The Car has been Transformed! (Methemoglobin)
Think Transformers! When the car is transformed, obviously there will be less People sitting in the seats. Infact, nobody can seat in the seats of a transformed car!

Those above are the causes of cyanosis, which happens when the red Cars are kinda "people-empty". Pallor, on the other hand, happens when there is lower number of red Cars on the Ferry. Less red Cars, less redder the Ferry is! You can have a million People swimming in the River, but if there are less red Cars on the Ferry, things are still gonna go pale!

Look at this Ferry, it has so little red Cars that..
..it made its surrounding go PALE!!

And hence, that's the analogy of the basic idea on what causes Pallor and Cyanosis. :)

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