Monday, February 7, 2011

Red and Blue

(This post is a draft - I still have to download the photos! Photos now added!)

Not in terms of whether you root for the University of Louisville or the University of Kentucky!

In terms of blood vessels.

Definitions: arteries carry blood away from the heart, veins carry blood toward the heart.  Red (on a model or diagram) denotes oxygenated blood, blue denotes deoxygenated blood.

While it is true that most of the time, the vessels carry oxygenated blood out into tissues (away from the heart) and return deoxygenated blood back toward the heart, this only holds true for the systemic circuit.

The pumonary circuit is an entirely different story, and this is why pulmonary arteries and pulmonary veins confuse so many students.

You see, after the oxygenated (red) blood goes to the tissues, and the deoxygenated (blue) blood returns to the heart, it then has to be pumped to the lungs to be re-oxygenated.

So the blood leaving the right side of the heart, going into the pulmonary arteries to travel to the lungs, is deoxygenated.  This is one case where you will see arteries depicted in figures and models as blue.

After its circuit through the lungs, the blood has become reoxygenated, and returns to the heart to be pumped to the body.  This is one one case where you will see veins depicted in figures and models as red.

So you can't really use blue and red as rules of thumb about veins and arteries, especially the vessels that come out of the heart.  You can, however, use what you know about where the blood is coming from, and where it is going next, to help you determine what vessels they are.

Here are some views of the models to help with this discussion.

This is a closeup of the pulmonary veins.  They are bringing blood into the heart (veins), into the left atrium.  They are carrying oxygenated blood (red) that will be pumped through the left side of the heart to the systemic circulation.  The fact that these vessels lead into the left atrium helps you to identify that they are pulmonary veins, also that they are carrying oxygenated blood helps you to know they just came from the lungs.



This is a closeup of the pulmonary arteries.  They are pumping the blood from the heart to the lungs.  From the right ventricle, a single vessel, called the pulmonary trunk, divides into the pulmonary arteries.  The fact that these vessels lead from the right ventricle helps you to identify that they are pulmonary arteries, also that they are carrying deoxygenated blood helps you to know the blood is headed to the lungs.



To help you make sure that you understand these vessels, make sure you can identify them correctly on different models.  Here they appear on the circulatory model:



and here they appear on the respiratory system model:


Pulmonary trunk is seen well in this picture leaving the right ventricle

Arteries away!

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