 Hi, guys. So we're here to talk about the cardiovascular system today. We are going to spend several lectures on the cardiovascular system. Today, we're going to look at the heart, and we're going to look at how the heart functions from a cellular perspective. The heart is made of cardiac muscle tissue, and having already looked in detail at skeletal muscle tissue, we kind of have a box that we can, a lens through which we can look at cardiac muscle and compare and contrast and see some similarities and differences with how cardiac muscle functions differently than skeletal muscle. We're also going to look at how the heart carries out its function of essentially being a pump, responsible for pumping blood throughout the body to get nutrients, good stuff to your cells, to take away the garbage, knowing that if our heart does not function properly, our cells will lack the food they need to carry out their jobs, and they'll be overflowed in garbage, which shuts down function equally as fast as not having enough food to fuel the function. Today's task is small. Today, we're going to look primarily at the cells that make up the heart. And we're going to do a little bit of bigger picture like how does the heart actually beat? And then in the next section, we're going to talk about the cardiac cycle in detail and some of the pressure issues and phenomena that we're going to see with that cardiac cycle. And then we're going to spend an entire lecture talking about blood. And then down the road, when we get to kidneys, we're going to talk about blood pressure. So before we do anything, we have to have a decent understanding of heart anatomy. So let's just review that since it is review for you, right? Okay. Let's talk about heart anatomy. First of all, the heart is basically expanded blood vessel. It is tubular, and that does mean cool. It's tubular and lined with cardiac muscle tissue. So this stuff that you see right here, this is cardiac muscle tissue. We have four chambers in our heart. So in your heart, there are four chambers. You have your atria. This would be my right atrium, and this would be my left atrium. Atria receive blood from somewhere in the body. The left atrium receives blood from the lungs. So blood from the lungs travels into the left atrium. The right atrium receives blood from the rest of the body. So blood from the rest of the body travels in to the right atrium. Blood in the right atrium, since it came from the body, it's dirty blood. It's used up old blood. Blood that just came from the lungs is delicious, healthy, high energy, lots of oxygen, blood, because it's been to the lungs to get refueled. From the atria, blood will travel into the ventricles. So this is my right ventricle and my left ventricle. The ventricles are pumping blood out. So atria receive blood from the body somewhere, and ventricles pump blood out. The right ventricle, since it got blood from the right atrium, and that was used up blood, the right ventricle is going to take the used up blood and pump it to, oh, the lungs. Why would we pump used up blood to the lungs? Because we're going to do gas exchange. We're going to get rid of the carbon dioxide and that used up blood, and we're going to replace that with oxygen. And then we have now fresh oxygenated blood to come back through. The fresh oxygenated blood that is now in the left ventricle that came from the lungs, that blood is going to go out through the aorta and it's going to go back to the body. Oh, except this time it's fresh and oxygenated. This is extremely broad. The important thing to remember is that in the lungs, what we're doing is we're replenishing the blood so that we have fresh oxygenated blood and we have fresh oxygenated blood that we can send to the body. And that's the whole point to keep circulating this blood. Now, we've got some other structures that we're going to talk about. We've got some valves that are going to be important because those guys are going to help us maintain a single direction of flow through the heart and that's really important. But before we go into any kind of bigger stuff, I want to talk about what's going on with the tissue that makes up the myocardium. What's the story with cardiac muscle tissue? We actually have a couple kinds of cells and some unique characteristics that we need to be aware of when looking at cardiac muscle cells. So let's go check them out.