Fall2011_Lab9

=Lab 9 - Cardiovascular system=

This lab we will go over what a cardiovascular system is good for in an animal, and how it applies to humans. We'll then use human subjects (students) to test the effect of inhalation, exhalation, and exercise on heart rate.

Mini-lecture:
- I made a mistake in lecture: The "right" side of your heart is the "right" side of a picture of a heart. So the left side of the picture of a heart is the "right" side. - Fluids carry nutrients and food and energy in organisms. Some organisms have a body that is filled with fluid, and no system of vessels that carry all of the fluids. This is an open circulatory system. But an open circulatory system works only if you are a small organism (think of an ameoba or a grasshopper). If it was possible for some organisms to adapt (via evolution) and have larger bodies, then these larger animals could take advantage of other food sources, other habitats, and be able to thrive in other environments. The evolution of larger bodies, though, means that the open circulatory system must change. Vessels evolved as a way to carry fluids long distances in the larger animals, among other things. A worm, for instance, has blood vessels, which can carry fluid from the head to the tail. Since it's not that far from the head to the tail of a worm, the fluid in the worm will not take very long to go from the head to the tail, but it will travel faster in vessels than it would in an open circulatory system. In addition, blood that is full of energy and nutrients can be somewhat separated from "old" blood that has had its nutrients and energy used up. - As animals evolved into larger body types, the need for a pumping system to propel the blood around the body became more advantageous. Also, the separation of old blood from fresh blood became more important. If you look at the hearts of worms, lizards, frogs, and then humans, you'll see that a central pump becomes larger, and the pump itself as well as the system of blood vessels is separated between old and fresh blood. The pumping mechanism is important because it allows nutrients to travel through the body efficiently, and the separation of old and fresh blood is important because this makes the delivery of nutrients and energy more efficient than by simple diffusion. - Human hearts have a distinct pattern for moving blood around. Importantly, the energy in the blood comes from oxygen, which is acquired by breathing. This is the same as in fish, but fish obviously have gills. Either way, the old blood must travel to the oxygen organ and get re-freshed with oxygen. Then it must go back to the heart and get pumped to the rest of the body. Also, small blood vessels called capillaries are so small that, when the fresh blood reaches the periphery of the body, then the fresh blood can be put into the muscles and tissue for energy use, and then old blood from the muscles and tissues and organs can be put into the circulatory system (via these capillaries) and sent back to the heart and then the oxygen organs to get re-filled. - The human heart is a complex system with lots of things going on. One of the thing is the ability to pump itself. Once the initial "spark" is applied at one part of the heart, then the entire heart will pump, first the top part of the heart (atrium), and then the ventricle (the bottom). There is a left and right side of the heart, and you think about it as if you are looking at a person, not as if you are looking at your heart. So your left side of your heart is the "right" side of the heart. Other things can affect the heart action, such as disease or stress. Exercise, obviously will cause a drop in oxygen in the muscles, and this will signal the heart to pump faster to pump more oxygen around the body. Also, simply inhaling and exhaling will change your heartbeat from moment-to-moment. As you inhale, it increases the pressure in your chest cavity, which will cause your heart rate to change. Likewise, as you exhale, it decreases the "interthoracic pressure", and this will also change the heart rate. The experiments in class will test this hypothesis. - In general, blood flows into the ventricles from the body and the lungs, and the atriums pump blood towards the lungs and out towards the body. This happens at the same time, at each pump of the heart, but slightly offset in time, which gives you the "lub-dub" sound.

- The pressure sensors in the thorax are in the aorta. They check the pressure of the blood system in the thorax (from the neck to the belly, excluding the arms). Along with heart rate and body temperature, organisms must regulate blood pressure to make sure it doesn't get out of control (another Goldilocks situation). If someone has stress situation, (e.g., when you have to run from a tiger, the flight-or-fight response), this will activate parts of the brain to tell the heart to speed up, because you need to get O2 to the muscles to keep you alive. This happens very quickly, and lasts as long as there is the high stress situation. Alternatively, when you inhale, you increase the pressure in the thorax, which pushes blood into the heart atriums. This leaves the blood vessels with less blood volume than normal, and this decreases blood pressure, especially when you take long inhales. When the pressure is low in the blood vessels, the body tries to raise the blood pressure by increasing the heart rate (thereby putting more blood volume into the system). So low pressure in the arteries affect the pressure sensors in the arteries, which signal your brainstem, which signals your heart to speed up. This is because, if there is not enough blood pressure in the body, organs and muscles may become injured. To counteract the low blood pressure (homeostatis of blood pressure), if the heart would beat faster, this would put more blood into the system, and raise blood pressure. This will return the blood pressure to the regular blood pressure level (viz. Goldilocks). When you inhale, your body is going to respond to the low blood pressure, and try to return the blood pressure to its normal level. Likewise, if you see a tiger and have to run, your brain will try to keep you alive and cause the heart to beat faster. If you have high blood pressure (and high heart rate) because you are concerned about a test you have to take, your heart will also beat faster, but not because this will help you do well on the test, but because of the ingrained homeostasis mechanism (flight or fight response) that would save you from physically dangerous situations (e.g., tigers).

Video on heart blood flow: http://www.youtube.com/watch?v=mH0QTWzU-xI

Human Heart explained.