This video will serve as an introduction to the circulatory system. Circulatory systems are the way which organisms distribute materials throughout their bodies. These materials include oxygen gas, carbon dioxide, nutrients, food molecules, hormones, and metabolic wastes. The reason that we need oxygen and food and nutrients is because all of our cells are performing cellular respiration. This is also why we need to get rid of CO2 and other metabolic wastes. Circulatory systems also aid in the regulation of our internal body temperature and assist with the immune system. There are three main components to circulatory systems. The central pump, which is the heart, the vascular system, the blood vessels, and the circulating fluid, which is the blood. There are two ways in which these components are organized. Circulatory systems can be open or closed. An open circulatory system has open-ended blood vessels, meaning that the fluid which is pumped into the blood vessels, and subemptying into the common body cavity. There is no difference between the blood and the interstitial fluid for these organisms. Interstitial fluid is the liquid which surrounds the tissues in the body, exchanging materials with the tissue cells. So, for organisms with an open circulatory system, blood and interstitial fluid are one and the same. The other way to organize the circulatory system is with closed circulatory systems. Close circulatory systems have continuous blood vessels, and the blood is never released from the blood vessels, except in cases of injury, where the blood vessels are broken. The chemical composition of blood in these diagrams is represented by the color of the blood vessels. The blue coloration represents the oxygenated blood. This is blood with low levels of oxygen gas, and high levels of CO2. The red coloration represents blood that is oxygenated, meaning they are the high level of oxygen gas, and a relatively low level of CO2. Does blood really change color based on its chemical composition? The answer is yes, but the change is not quite as drastic as we see here. Deoxygenated blood is going to be a very dark maroon color. If you have ever donated blood, the blood that was collected from the veins in your arm is deoxygenated, so the blood that is collected would be very dark in appearance. Whenever blood is exposed to air, the oxygen is collected, which is why when you accidentally cut yourself, the blood at the side of the wound will be a bright red in color, because the blood is exposed to the air. Humans and all vertebrates have a closed circulatory system. It is still used to distribute materials throughout the body and participate in gas exchange. It is just that the blood is distinct from the interstitial fluid. These two fluids are able to exchange small molecules with each other by diffusion through the blood vessels, but the red blood cells themselves are not able to leave the blood vessels. Humans and all other vertebrates have a closed circulatory system, while arthropods and many other invertebrates have an open circulatory system. The vertebrate circulatory system is known as the cardiovascular system. Cardio refers to the heart, and vascular means blood vessels, so we know most of the components simply from its name. Also a part of this system is the circulating fluid. The cardiovascular system of mammals and birds is made up of a heart with four chambers and two distinct circuits of blood flow. The two upper chambers are called atria, while the two lower chambers are called ventricles. The names of these circuits are the pulmonary circuit, which is carrying blood from the heart to the lungs and then back to the heart again, and the systemic circuit, which carries blood from the heart to the rest of the body and back to the heart again. The chambers on the right side of the heart pump the blood to the pulmonary circuit, which eventually leads to the chambers on the left side of the heart. The left side of the heart has chambers which pumps blood to the systemic circuit, which eventually returns the blood to the right chambers. Remember, any diagrams that you see of the heart are showing you the heart as if the patient was standing in front of you, so they're left as you are right and vice versa. In this way, blood must travel through both circuits completely before it is able to return to the first. Now for some questions. What is the name of the fluid surrounding the tissues within the body? That saliva, interstitial fluid, gastric juice, coolade, or all of the above are just as likely. A closed circulatory system is not able to exchange or transport materials within the body, so say true statement or a false statement. Which circuit carries blood between the heart and the lungs? It's at the systemic circuit, the hepatic circuit, the cardiocircate, the pulmonary circuit, or the short circuit.