Laminar Flow, Turbulent Flow, and the Circulatory System

Laminar Flow, Turbulent Flow, and the Circulatory System

Now that I am back home and have more free time, I have started to prepare for the MCAT. One of the sections I was reviewing recently was the circulatory system, where I recognized the importance of laminar and turbulent flow within this system. 

The circulation of blood cells within the body more or less follows a laminar flow. The blood cells in the middle of a vessel move the fastest, while blood cells near the periphery of the vessel move more slowly due to friction between blood cells, plasma, and other blood components and endothelial cells. The “middle blood” moves faster or slower depending upon the size of the vein or capillary, but we will simplify here and assume that all blood follows the same laminar flow. 

Although some blood cells may be travelling faster than others, we can see in the diagram above that the blood cells all travel in the same uniform direction. Issues arise in the circulatory system when turbulent flow is introduced. Some turbulent flow occurs naturally in the body, such as in the atria of the heart. In addition, the aorta has been observed to dilate slowly with age; this dilation can have no effect or it can help contribute to the symptoms of cardiovascular disease. Turbulent flow presents a larger problem, however, in the instance of plaque build-ups around the body. When plaque begins to build up in an artery, the velocity of blood cells passing through the now smaller artery opening increases. The equation for laminar flow is given below: 

p1A1v1 = p2A2v2

The issue with plaque build-up is not the increase in speed of the blood cells, but with the turbulent flow that creates “eddies” in the blood after passing the plaque build up. These blood eddies caused by turbulent flow can cause blood stagnation, inflammation, or infection. In addition, these turbulent-flow blood eddies have been implicated in conditions such as heart attacks, aneurysms, and thromboses. The image on the bottom to the left depicts turbulent flow and blood eddies (in comparison to the healthy laminar flow above), and the bottom right image is a simulation of how turbulent flow contributes to a hypothetical thrombosis. 

Literature Cited:

https://www.frontiersin.org/articles/10.3389/fphys.2018.00036/full

http://mriquestions.com/laminar-v-turbulent.html

https://basicmedicalkey.com/alterations-in-blood-flow/

https://www.youtube.com/watch?v=nF6nJE-FkWM