Thursday, July 2, 2009

Causes of Hypoxemia Part 1

So what can cause hypoxemia?

Remember the people swimming-ferry analogy?

As you have recalled, hypoxemia would be as though there are very little people swimming in the river. So what can cause less people to swim in the river?

Cause number 1 :
Less people arrive at the river bank. (ventilation defects)

When less people arrive at the river bank, obviously there will be less people swimming in the river. In the same way, if less there is less oxygen delivered to the lung (maybe because the lung is collapsed like in Respiratory Distress Syndrome), there will be less oxygen being able to get into the blood from the alveoli.

Up next : Cause number 2!

Monday, June 15, 2009

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.. made its surrounding go PALE!!

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

Sunday, June 14, 2009

Emergency Joke

A tired doctor was awakened by a phone call in the middle of the night.

"Please doctor, please, could you come right over? My child just swallowed a Viagra!"

The doctor was just about to leave his house when the phone rang again. "Oh, Doctor, you don't have to come after all," said the woman with a sigh of relief. "My husband just found another one."

Saturday, June 13, 2009

Ur Smile Makes Learning Easy =)

..and that's what USMLE stands for!

So remember to smile and enjoy your studies, and stay positive! Our mind is truly amazing, and we must not let it feel down and stressed so much alright? Let it be happy and it will retain information happily!

Ur Smile Makes Learning Easy = USMLE

Genetics : Lac Operon

What is it and how does it work?

One day, we (prokaryotes) realise that our normal food, rice/bread/wheat, (glucose) is no more!! And the only thing we can do now, is to eat delivered Hot Turkey (lactose) !
Now, the delivered Hot Turkey is outside our doorstep, but the thing is.. we are unable to just take in the Hot Turkey and eat it just like that, because it is sizzling Hot and super big!

What we need are gloves (lactose permease) which we can use to help us bring in the Hot Turkey and then knife (Beta-galactosidase) cut it up. But we do not have gloves or knife! Luckily..we can order them online, using our computer (gene).
Therefore, imagine our computer (gene), which we can order :
-gloves (lactose permease) , to bring in that Hot Turkey from outside our door
-knifes (Beta-galactosidase) , to cut up that turkey so we can eat it

But the thing is, we can't access our computer to order that glove and knife. That is because our computer is blocked by a password (Lac Repressor Protein), and it also has no power supply (low cAMP and therefore inactive CAP).

Therefore, that is the Lac Operon, which is a gene, on the prokaryotes, that composes of a) the codes to make proteins for lactose metabolism and also b) the regulatory region for those proteins.
Just like our computer, which composes of a) the order form for the tools needed to bring in and cut up that Hot Turkey, and also b) what determines whether we get to order the gloves and knife, which is the password, and the power supply of the computer!

And so how then do we get to order the tools needed so that we can bring in and cut up the Hot Turkey?
1) When our computer detects that there are Hot Turkeys around our house (lactose present), it automatically allows us to access it, without a password! (prevents repressor binding)
2) When our computer detects that we really do not have normal food left (low glucose), it automatically turns on its power supply (increase cAMP and activate CAP), so we can use it to order gloves and knife to bring in and cut up that Hot Turkey!

And that, is an analogy on how the Lac Operon works in the Prokaryotes. =)

The road not taken.

"Two roads diverged in a wood, and I—
I took the one less traveled by,
and that has made all the difference."

And it does make all the difference.
Congratulations. If you are reading this, you most likely are like me, an International Medical Graduate, who is on his/her journey to become a full fledged physician in United States.

This road is not easy. But we have made the choice experience it. Venture with me into this path, and let’s make this voyage an enjoyable experience, to a great score in the USMLE.

"I took the one less traveled by ...and it was in fact a much more fascinating one."