Sunday, October 29, 2017

Stuff I Learned - Circulatory System

When I was a kid, my family drove a ginormous Ford van. True to the times, it was fully customized with the requisite shag carpeting, wood paneling and captain's chairs. Sweet.

In addition to feeling like a rolling living room, it had two huge fuel tanks. Each tank was probably about as big as my entire Smart Car, and the range of the Econoline was remarkably long. It felt like refueling took the better part of the day, though I scarcely remember ever stopping for gas in that van. I have fond late-70's memories of road trips to my family's cabin, track meets, and ski trips in that van - mostly accomplished without having to stop to refuel.

Pedestrians - get out of the way!
Small window made it hard to see
out of groovy vans.
Why am I reminiscing about the van that caused global warming? I'm mentioning this van because it had a large capacity to carry fluid, and it did so by having more than one reservoir to handle all its capacity. The human body similarly has a lot of fluid to carry around - in the body's case, the fluid I'm referencing is blood.

Circulating blood is necessary for life, and the body is engineered with lots of blood capacity. Copious blood capacity is a good thing, as having just enough blood to get by would mean that even a small wound and blood loss would be fatal. Evolutionary pressures favored the creatures that had extra blood carrying capacity, and we now walk around with reservoirs of blood that are carried in different tanks in our bodies.

One of the tanks carrying our extra blood capacity are the abdominal organs (splanchnic region). As you're reading this blog, there are likely at least a few pints of blood sloshing around in your body that are not actively involved in maintaining your life. They're in reserve, waiting to perfuse tissues, as needed.

This blood capacity isn't just for protecting against blood loss. When you exercise, this extra blood capacity is also very useful. Exercising muscles require lots of nutrients and oxygen, and it's the blood that carries these substances to the muscles. In addition, exercising muscles release lots of waste by-products that need to be carried away from from the action. While the body has a lot of blood capacity, the working muscles have a huge appetite for blood, and there is not enough blood to supply every tissue all at once.

The body's response is clever - during exercise, blood supply is directed to the working muscles, and away from areas that are less important in supporting the activity. Your body automatically reapportions blood away from lower-priority tasks and toward higher-priority tasks.

After I finish writing this blog, for example, I'm planning to head out to Blue Mound State Park for an ~8-mile trail run. During that run, my legs will require a lot of blood - some of the major muscles will require to the tune of 3-5 liters of blood flow per minute. That's a lot of blood, and that rate of consumption would even exhaust the volumetric carrying capacity of the 1977 Econoline van!

My body will make some interesting adaptations to accommodate this activity. Once I decide to begin running, my brain stem will signal my sympathetic nervous system to initiate a modest fight/flight/freeze response. This sympathetic activation will increase my heart rate and constrict the blood vessels throughout my body. In the first minutes of my run, my rest and digest response will diminish, and my heart rate will rapidly increase due to this parasympathetic withdrawal.

This blog isn't really about vans, though I now have vans on my mind.
From ages 16 - 35, I primarily drove VW vans.
As the exercise continues, metaboreceptors in my muscles will sense accumulating waste byproducts, and will send signals to my brainstem requesting greater blood flow. My body will respond by opening up the floodgates of blood flow to the working muscles, while further restricting blood flow to any muscles that aren't working. In addition to redirecting blood flow away from non-working muscles and toward working muscles, my body will more or less shut down my GI tract, and divert the huge amount of blood in the splanchnic reservoir toward my working muscles.

In the 1977 Econoline van, a switch on the dashboard shifted fuel supply from one tank to the other tank. In the human body, the shifting of blood flow occurs automatically. During this morning's run, I will not need to focus on or visualize redirecting blood flow  - it happens organically thanks to the vast intelligence that infuses the human body.

When I run, I try to reduce the degree to which I control my movements. Most of my conscious awareness of running is just that - awareness. I practice feeling my feet contacting the ground, sensing the movement of prana/breath, and enjoying the unfolding scenery that surrounds me. Particularly for those of us who have embraced movement practices, it can be tempting to micromanage movement experiences.

This micromanaging can take various forms, though the most common forms are holding the body in the right way, and/or controlling breathing.  As I've mentioned in previous blog entries, I encourage you to resist the temptation to use movement practices as a means to reinforce controlling tendencies, and use movement and movement practices to connect with the vast intelligence that pervades the human body.

Have a great week!


1 comment:

Nancy O said...

Thanks Scott. I enjoy your blogs. Good teacher who makes the complicated simple. I'm going to go drag out my winter running duds!