The Heart is Not a Pump
Day 113, 69-44
It was another gray morning and cold to boot! So no spectacular sunrise or dramatic pooch portraits today. What else can I do but make a dramatic statement? I suppose I could immediately walk it back a little, because the heart does function as a pump, a little. But it is probably not nearly as much of a pump as conventional wisdom/education leads us to believe.
For starters, a little thought experiment gets us to question how the heart could possibly do all the work it would need to do to get blood throughout the body. Of course the exact number varies depending on the size of the person, but most estimates of length of all the blood vessels in the body approach 100,000 miles! 60,000 of that is capillaries, the super teeny tiny vessels where nutrient pickup and waste drop-off occur. What's more, those capillaries are actually a smaller diameter than that of the average red blood cell! So, we have miles of pipes through which we are pushing a viscous (very thick) liquid, with chunks that are too big for the pipe! Now, those chunks can compress and deform to fit through, and it may help that there is a push and pull since the circulatory system is (hopefully) a vacuum without air bubbles in it. But that is a major head of pressure and back up that would form. So what sorcery is at work behind the scenes?
It turns out, it's not magic, it's electricity and magnetism! First off, blood is seemingly very sticky, so we need to figure out a way to make it more slippery to move smoothly through our vessels. Enter Zeta potential. This is a measure of the net charge at the surface of a cell. RBC's maintain a net negative charge, keeping them from sticking together. The interior vessel wall also has a net negative charge, which means the RBC's won't stick there either. In fact, the repulsive force pushes the RBC's along, like tiny Mag-Lev trains.
Now, as I always like to say, everything in moderation. In addition to repulsion, there is a little bit of electrostatic attraction in the mix as well. The serum the RBC's are floating in have a net positive charge, which helps draw RBC's forward as a preceding RBC vacates. Picture the point where a capillary is joining back up with a venule. You have an area of slow moving cells (capillary) joining a fast moving area. Similar to a car trying to get onto a busy highway, these cells have trouble exiting the capillary. But the net positive charge of the serum pulls them in at just the right time to get in line. This also helps keep blood moving forward while in the larger vessel.
There is a lot more, but I'm running out of time. Little Miss Sunshine has to get to a horse riding lession. So the TL;DR version is this. The heart is a pump, but not very much. It depends on blood to be very free flowing. There is also some peristaltic (squeezing) action within the vasculature to help move things along. The heart, more than a pump, is also a magnet, like a boosting station on the Mag-Lev train line. Oh, it also does one more thing. It vortexes blood. The simple effect is to think about improving flow, like swirling the water in a bottle to help it pour out rather than waiting for it to glug-glug out. It also facilitates a phase change in water. That is the so-called Fourth Phase of Water. More on that another day.