The Zen of Cardiac Blood Flow


So hearts come color coded now? Oh man, surgeons have it easy

I’ve given up on learning the secrets to winning a woman’s heart and settled for learning
how they tick…or should I say beat. Well, here is what I’ve learned so far…

A Word or Two about Gravity

Yes, gravity is always an issue. It acts on blood moving through the body no differently than
it acts on feathers, wooden balls, Chuck E. Cheese tokens or whatever else that 16th century wild man
Galileo decided to drop from tall buildings in Pisa. The heart performs remarkably well
despite blood’s downstream tendencies, pumping against the stream so that no organ gets
cut out of the action.

Hey don’t fall asleep on me yet. I’m only telling you this painfully obvious fact to point out
that since the heart muscle directs blood flow there really is no reason to go looking uphill to figure out where it all begins. Which direction you choose to describe blood flow starting from is really a matter of perspective, by that I mean the fate of oxygenated versus deoxygenated blood. Since it’s all about me, I’m going to start with the flow of oxygenated blood traveling from the lungs.

Listed in order

Oxygenated Blood

  1. Lungs
  2. pulmonary veins
  3. left atrium
  4. bicuspid valve/atrioventricular valve
  5. left ventricle
  6. aorta – its branching arteries which feed the systemic circulation

Deoxygenated Blood

  1. superior & inferior vena cava
  2. right atrium
  3. tricuspid valve/right atrioventricular valve
  4. right ventricle
  5. pulmonary semilunar valve
  6. pulmonary artery/trunk
  7. lungs

The tune goes like this…


I was always too busy pumping the brakes and swearing to notice the striking similarities

So the lungs have done their part, allowing red blood cells to exchange their CO2 from the
tissues for oxygen from the aveoli into neighboring capillary beds. Once oxygenated, the
blood returns to the heart from the lungs by a set of pulmonary veins which empty into the
Left atrium like jumper cables to a battery. Medieval architects constructed atriums in
cathedrals to serve as the first giant, open chambers that you would enter. The atriums of
the heart are constructed in much the same way (that’s right, I learned that in public
school). Blood from the atrium enters into the left ventricle after passing through the
bicuspid valve. As the ventricle contracts the oxygen charged blood moves into the aorta
from which it can flow freely into the wild (or the systemic circulation making up the rest of
the body if you want to be boring). The aorta is a major intersection of arteries that branches
off to the body, the Jersey Turnpike of the vascular system.

So now that the blood has had time to mingle with the organs and tissues, toured the
sights, been places…what happens in Vegas stays in Vegas that sort of thing, it is just
about tapped out of oxygen. The blood then returns to the heart from two different
directions. Blood from the upper body will be entering through the superior vena cava and
the blood coming from downtown will be entering through the inferior vena cava. Much like it did on the left, blood will first enter the right atrium. Blood will then flow into the right
ventricle after it has passed through the double doors of the tricuspid valve. Contraction of
the ventricle will move the deoxygenated blood into the pulmonary artery where it will revisit
the lungs for more of that sweet sweet oxgen. I love a happy ending.

A few things to consider..

Valves are a pretty nifty thing to have in a fluid environment under relatively high pressure. The heart has a lot of blood to move and can’t just take a deep breath and let it all out at once
like the big bad wolf. It needs to take a lot of smaller breaths, relax and contract. The valves
stop the blood we started with from being forced backwards under the pressure every time
the heart muscle changes it’s shape.

The left and right sides of the heart are cleverly separated from each other by septa. These are thick, tough walls of cardiac muscle that keep the oxygenated blood from mixing it up with the deoxygenated blood among the atria and ventricles.

The pulmonary veins are kind of special. If you’ve ever studied the difference between arteries and veins, the veins are typically illustrated in textbooks as blue and the arteries are always red. Illustrators do this to emphasize the oxygenated versus deoxygenated nature of the vessels. So then non-conformists like the pulmonary veins come along and throw everything off because they deliver oxygenated blood to the heart. So now what color should we use?

Anyway, I hope this helps you on your way towards academic rock stardom. Stay classy my friends and never stop learning 🙂

Oh Those Naughty Diagrams

Do diagrams and biochemical pathways make you shrivel up like cold McDonald’s fries underneath your driver’s seat? Allow me to offer some friendly advice.

Ah sweet clarity, good to the last drop…

Classic animal cell model from your youth. Note the intricate jelly bean design

Classic animal cell model from your youth. Note the intricate jelly bean design

Today we’re going to dig deep…haha no no way deep, into the pscyhe, into your most primitive, raw memories of how you first learned about the human cell. Now close your eyes and imagine (only imagine yourself closing your eyes. Please keep reading). There you are, adorable, innocent little you ready to dive in, converse first, into a brand-spankin new science textbook, all shiny and full of promise. Your teacher instructs all of you to turn to the 1st chapter and there it is….the cell. The ribosomes are red and round. The mitochondria are not unlike yellow jelly bellies, and have you ever seen a smoother endoplasmic reticulum? I doubt it. So you’re staring intently at this artist’s rendition of the cell, and it’s huge…like really huge. Now keep in mind that kids are sponges right, you show them a powerful representative image of a cell and explain to them that it’s the most basic unit of all living things and they will remember it. There’s just one thing…cells aren’t huge they’re teeny tiny, and cells don’t just have two or three ribosomes. They have thousands. No, I’m not picking on teachers or textbooks because honestly, biology is intensly complex at times and it’s good to get a firm grasp of the basics. Besides, any decent teacher or text will go on to explain that cells are tiny and that you have a couple trillion in your body. Most kids get that. What I’m suggesting is that when it comes time to add more dimensions to our learning we have a hard time letting go and don’t realize it. A REALLY really hard time. I can’t tell you how many times some one will mention the state of Maine and a giant lobster pops inside my head.

Let’s fast forward to highschool biology class. I’ll never forget it. It was 8am – the caustic waft of chalk dust twirling in the cold, fluorescent light and through the smoke my drowsy, adolescent eyes make out an old, familiar sight traced on the chalk board, the human cell. For a time, all is well. Suddenly, the two dimensional world of my childhood takes a nasty turn down a sketchy alley called “Cellular Metabolism.” The teacher directs our attention to the humble mitochondria “the power house of the cell.” She begins to speak of biochemical pathways, of co-factors, glucose, and enzymes…oh my! It is a complex world indeed, but try as I might to wrap my head around these new concepts all I see are the same two-dimensional jelly beans from my youth.

There are those of us who can compartmentalize, who can simply take that new information and memorize it…learn all the sequences and reactions, and simply spit them back out when test time comes. I call this kind of learning “renting.” That knowledge has no depth or dimensions  It doesn’t really belong to you. Understanding where reactions take place in the cell, how often they occur, and the alternatives to those reactions is an experience that belongs to you. Yes, if you have the ability to just absorb pure facts and recall them my hat goes off to you, but we as students should always always always make an effort to incorporate a sense of scale into our learning or it WILL come back to haunt us. Allow me to demonstrate.

the tune goes like this…

Let’s say I just received new information: “Chickpeas are an excellent source of protein, but they do not provide a complete source of protein.”

I will now trace back through the steps of what I already know. WARNING this may seem tedious and possibly annoying to many of you, but it really does help.

Chickpeas are an excellent source of amino acids, which form chains that make up protein. There are 9 essential amino acids that our body’s need to function. Amino acid chains are produced by ribosomes in our cells from information contained within messenger RNA which is transcribed from a gene which is a specific sequence of DNA, which is tightly bound and coiled around histone proteins. Many tightly packaged bundles of DNA and protein make up chromosomes contained within the nucleus of our cells. The ENd.

No, I don’t do this for every morsel of new information I learn, but it is a great way to ground yourself when you begin to feel overwhelmed.

Now when it comes to biochemical pathways don’t let those intimidate you either. Allow me to quote myself from another lesson;

When approaching any biochemical pathway for the first time you should always ask yourself what factors (enzymes, organic molecules, catalytic elements) are already present within the system. Next, you should ask yourself what factors will be introduced into that system. That is the rhythm of a pathway; what’s already there, what gets introduced, and what gets made when we put them together.”

I just thought that I would take this time to throw out a friendly reminder that when things start to get a little hot and heavy in the classroom (or the boardroom) seek out that sense of scale. That is all for now my friends. As always, stay classy and never stop learning.