This is DD11 final project for WWS1, written completely independently from choosing the topic to completion of final product. I've given her some feedback, but I would love outside opinion for my own reference, please! She's my eldest, and I'm often unsure of where she stands...
She does have all the direct quotes footnoted, but they're not copying here for me.
BLOOD AND CIRCULATION
Circulation is one of the most important processes in the human body. If it stops, you’re dead. It is as complex as anything, but also very simple. It all begins in the chest. When you breathe in, you breathe in oxygen, which your body needs in order to survive. But how does that oxygen get around your body? Well, that’s where circulation comes in.
Once it is gets into the lungs via the nose or mouth, the oxygen hitches a ride on some red blood cells and zips along the pulmonary vein to the heart.(Note: the pulmonary vein is the only vein that carries oxygen. All of the others carry carbon dioxide. Similarly, the pulmonary artery is the only artery that carries carbon dioxide, and all of the others carry oxygen. Scientists call them that because arteries carry blood from the heart and veins carry blood to the heart.) “Inside, it [the heart] has four…chambers…each top chamber is called an atrium…each bottom chamber is called a ventricle.”
At the beginning of its journey, the oxygenated blood (blood with oxygen) is pushed into the left atrium.“In each opening [between atrium and ventricle] …a valve…makes sure the blood flows in one direction.” Therefore, the blood now comes into the left ventricle, then shoots into the aorta, the body’s largest artery, and out of the heart. Then the blood traveles through the arteries and drops the oxygen off at different parts of the body. Now, because there is a set amount of blood in the body, that blood-also carrying lots of carbon dioxide (a poisonous gas)-needs to get back to the heart and the lungs. But how?
At this point, the arteries start to get narrower. Soon, they get so narrow that they are not arteries anymore, but ridiculously tiny blood vessels called capillaries. Then the blood comes into these capillaries and travels along them until the blood vessel starts to get larger and becomes a teeny-tiny vein, but a vein nonetheless. Then it slips through the vein-which keeps getting bigger and bigger-until it gets back to the heart. At its destination, the deoxygenated blood comes into the right atrium through the vena cava veins first. Finally, it swoops into the right ventricle and back to the lungs through the pulmonary arteries, and you breathe out. This whole process takes place in less than a couple of seconds, maybe even less than one. And from the moment that you are born, to the moment you die, it never stops.
Blood is very important in circulation. “Whole blood…delivers oxygen…; it removes carbon dioxide and cell waste…; it transports nutrients…; it carries hormones, medication, and enzymes…; it clots to preserve…blood…; it delivers antibodies and fights infections; and it helps regulate body temperature.” Some people feel faint at the sight or even the mention of blood, but there’s really nothing to get woozy about. Blood is truly fascinating. “There is an average of 4-5 liters of blood in an adult.” Since there is so little of this red liquid, the body works very hard to keep it inside. It does so with little cells called platelets.
When you get a paper cut, or your sweet little puppy decides to nip you and punctures your skin, or the school bully trips you and you land on the sidewalk and scrape your knees and elbows, you start to bleed. Your body knows it has to save the rest of your blood from leaking out, it really does. But how does it do that?
Once you start to bleed, the punctured blood vessel automatically narrows. Almost immediately, platelets swim over to the hole and stick there. “A special protein” called prothrombin also helps clog the wound, and soon you get a scab, which will eventually fall off by itself. Don’t try to peel it off!
Platelets, like all other blood cells, “live” in one of the three layers of blood. Those three layers are plasma, red blood cells, and the buffy coat. Red blood cells (duh) contain red blood cells, the buffy coat contains platelets and white blood cells, and plasma contains everything else, like sugars, salts, and proteins. Now you know what platelets are, but what are those white and red blood cells?
Red blood cells carry oxygen and carbon dioxide. They also carry a protein called hemoglobin, which they can’t carry the gases without. They are red, of course, and shaped like doughnuts, just without the holes. They are also flexible. There are billions-maybe trillions-of red blood cells in the body. In fact, “in one drop of blood, there are approximately…300 million RBCs [red blood cells].” That’s a lot! And all of them are basically the same, because there is only one type of red blood cell.
White blood cells (WBCs) are a little more diverse, but there are much, much fewer of them. “For every 600 RBCs, there is one WBC.” There are tons of different types of WBCs, but they all do the same job. That is job is to protect your body from bacteria, viruses, and infections. When an invader like a flu virus comes into your body, a WBC comes over to it and chomps it up like a potato chip! Two types of WBCs, by the way, are called lymphocytes and leukocytes. Another type is called a natural killer cell.
And finally, though some people find blood frightening, maybe even have nightmares about it, it’s truly a fascinating and vital liquid that all of us have inside our bodies, and nothing to be afraid of.