 In this video I'm going to introduce blood, but I want to start with one of the most amazing facts in all of human anatomy and physiology. If I were to ask you what are you made of, what might you say? Water would be a good answer. It might think muscle, bone, these types of things. But from a cell standpoint, you are somewhere between 70% to 80% red blood cells. That shows you how important these cells are. Now how can you make sense of this? Well, there are trillions of red blood cells somewhere in the neighborhood of 23 to 25 trillion red blood cells in your body. There's only 30 to 35 trillion cells in your body. So from a cell count standpoint, you are almost all red blood cell. Now of course these are very tiny cells and water isn't cellular, so from a volume standpoint that isn't true. But from a cell standpoint that is actually true. So let's talk about blood. Why is it even important? Small, single cell organisms don't need blood. Small organisms don't need blood. Blood is the reason that we can be so large. Blood is also the reason that we can have organs that have a division of labor. Organs that can each do their own job because blood is what carries nutrients to all these different organs and structures and carries all the waste products back. So we would think about that as its key function, right? But there are lots of other functions too. It plays a role in defense and that's because of your white blood cells, right? They play a big role in your immune function. We'll cover that a little bit here this chapter and a lot more when we talk about the immune system in just a few chapters. It plays a huge role in the distribution of heat and that's because, like you'll see in a moment, blood is warmer than the rest of your body. So your body uses blood and your skin like a radiator system to carry excess heat away or to trap heat at your core. It plays countless roles in the maintenance of homeostasis, the things we've talked about throughout the semester, by carrying hormones and all sorts of chemical messengers that keep our body in balance. And then lastly, it plays a big role in the maintenance of our body's pH and we'll see why. There's lots of reasons but the glaring reason is that carbon dioxide is actually an acid. It becomes carbonic acid anyways, which is a weak acid. So how much carbon dioxide we're carrying plays a major role in what the pH of our body fluids are. All right, just some basic facts about blood and then we'll break it down into these three key components here in just a moment. Blood is thicker than water like you've heard. The blood is about five times more viscous than water, which means it's resistant to flow or more syrupy than water. That's what viscosity means. So blood is five times more viscous than water. Like I just mentioned, blood is warmer than the rest of your body. Your normal core temperature is 98.6 degrees Fahrenheit. Blood usually runs at 100.4 degrees. It has to do with the friction and the resistance in your blood vessels. Even when you're young and you have healthy, smooth blood vessels, there's some resistance and friction and that actually heats things up. Like if you were to rub your hands together, they're going to get warmer. So blood is slightly warmer than the rest of your body. pH of blood normally is 7.4, but it runs in a range of 7.35 to 7.45. In a later chapter, we'll talk about things that cause the pH to drop outside of those normal ranges and then how to hopefully deal with them. We talked about the cell number, standpoint 23 trillion red blood cells in your body, give or take. But the amount of blood is usually in the five to six liter range for a man and four to five liters for a woman. It's size dependent, but so five liters is a good safe number. So we see here, we see three different blood samples that have been spun in a centrifuge. The top is the plasma. So let's look at the normal blood. We won't talk about anemia or polysothemia here, but you see that obviously you can get some abnormal results with blood as well, like every other part of your body. But plasma is going to be the fluid portion of blood. It's primarily water and that's very important because water is the universal solvent. It carries things that can be dissolved in it. So about 45 to 65% give or take of your blood is plasma. Then this Buffy coat is going to be in the middle. That's going to be where your white blood cells are and your platelets. And you can see that there's not a lot there compared to red blood cells. And then we have the red blood cells there at the bottom. Excuse me, I apologize. I'm probably going to cough a lot today. I don't feel great, but let's start with looking at what plasma is. So we just said that plasma is somewhere in that 45 to 65% of your blood. As you can see from the top here, though, it is 92% water. So the huge majority of your plasma is water. And its job is to carry things that are water soluble. They'll dissolve right in the water. Things that can't be dissolved in your water are going to be carried by the plasma proteins. So as you can see here, about 7% of your blood plasma is plasma proteins. And there are three key types and you have to know them all. You have the albumin, the globulins and fibrinogen. So albumin, the first thing I think of is that it is a transporter. So it is a very important transporter. But also as you read there, it maintains osmotic concentrations. We'll cover this more in just a couple of chapters. But if you don't have enough protein in your blood, then you're going to be losing too much fluid into your body. And you're going to be drawing too little of it back in, which is going to lead to things like ascites. So someone has a swollen abdomen full of fluid. It's usually because in the United States it'd be liver failure, liver cancer, these types of things. So they're not producing enough albumin. But if you see it in the developing world, it could be that someone is starving and they're so protein malnourished that they can't make albumin. So yes, albumin is a transporter, but don't forget that piece. It maintains osmotic concentration. What's the most, I mean, there's all sorts of different binding proteins that are going to be albumins there. The globulins, they're a little unique because most of them are made by the liver just like your albumins are, but not all of them. So the alpha and beta globulins, they're primarily going to be transporters. Think about them as transporters. But the gamma globulins are your immunoglobulins, like IgG, IgA, IgM. We'll cover them in a few chapters. They're actually produced by plasma cells. So a plasma cell is one of your lymphocytes, a B cell, becomes a plasma cell to make those antibodies and they're going to be a huge part of your immune system. So that's albumin and the globulins. The third plasma protein is fibrinogen and this plays a huge role in blood clotting. The end result of our blood clotting cascade is fibrinogen becoming fibrin. So just remember, fibrinogen, critical role in blood clotting. The other less than 1% that's left is going to be hormones and other chemicals and gases and nutrients that are dissolved in your blood and being carried there. All right, so that is plasma. The rest of your blood is going to be called your formed elements. So here you see some pictures of them. Now why don't I call them the blood cells? So you may have learned them as your blood cells, but they're not actually cells. Red blood cells technically aren't cells anymore. They used to be, but they lost their organelles. They lost their nucleus, so they're no longer classified as a cell. And platelets aren't cells. They're cell fragments. They come from a huge cell called a mega karyocyte, but that one cell makes 2, 3,000 of these little cell fragments. So red blood cells used to be cells, platelets are cell fragments. So the only actual cells in your quote unquote blood cells are your leukocytes or your white blood cells. So that's why we call them formed elements. Okay, so that is a quick introduction to blood, why it's significant, what makes it amazing, and what it's made up of. We'll go into detail on all the other structures moving forward. Okay, I hope this helps. Have a wonderful day. Be blessed.