Don’t Make this Mistake When Teaching About Blood Vessels!

I have worked with frustrated students many times.  Their cheeks will be red and their voice begins to rise as they tell me that the model key is wrong (for example).  I know what is coming next and they aren’t going to like it.  Humans don’t like being wrong, as a result we aren’t always receptive to correction.  I usually know what topics students will stumble on and can anticipate in order to avoid a fall.  One of these stumbling spots is about blood vessels.

As I write this I both smile and grimace, because it is as predictable as the sky being blue.   Students make misconceptions all one their own.  The teacher isn’t involved in most instances.  This particular problem is related to our perception.  The blue and red colors that are used in labelling the cardiovascular system are killing me.

 The number one mistake about blood vessels is that students assume the color on models tells you whether a vessel is an artery or vein.  It simply isn’t true.  This misconception becomes a very big deal in Anatomy & Physiology and upper level science and/or allied health courses.

I know you probably don’t need the lesson, but I feel like I need to provide the background to explain the student thought process.  Students assume, incorrectly, that arteries carry oxygenated blood and veins carry deoxgyenated blood.

The colors represented on models indicate the oxygen level, but do NOT indicate whether a vessel is a vein or artery.  The direction of blood flow determines blood vessel names.  Arteries carry blood Away from the heart.  Veins return blood to the heart.

In the systemic circulation, the aorta and other arteries are carrying oxygenated blood away from the heart and delivering it to the tissues.   In addition, the veins return deoxygenated blood to the heart.  There is a coincidental overlap between the presence of oxygen (indicated by color) and the name of the vessel (which is based on direction of blood flow).

This overlap is not true in the pulmonary circulation (and the same is true with regards to adaptations of the  fetal circulation) the color does not correlate with a vessel name.  Pulmonary arteries carry deoxygenated blood away from the heart to the lungs.  Veins are typically blue/purple.  The color indicates the presence of deoxygenated blood. Pulmonary veins return blood to the heart. This blood is oxygenated at the alveoli of the lungs , therefore these veins are red because they are carrying oxygenated blood.

I assume that students are making this incorrect correlation all on their own.  Like in the case of the cell, it is important to point out the fallacy of their thought process so that we can prevent the loss of time and energy fixing the problem later.  I always try to explain the difference between the color and the names.  They are telling you two different sets of information. The direction of blood flood determines the name of blood vessels. The colors used in diagrams and models indicate the presence of oxygen (red) or absence (blue/purple).  I also point out the examples that will help to dissolve their misconception (usually the pulmonary artery and vein).

I love talking with you and learning tips and tricks to help my students.  Check out this free live workshop on November 27 at 7:30 PM CST.   I will be talking about adding additional teaching strategies to a normal lecture class period.  There will be a live Q&A at the end for any questions you might have about the workshop or anything else.  If you can’t make the live event, sign up and you will receive a link to the replay by email.