In this video we'll be looking at the human circulatory system. We'll see the route that blood follows from the heart to the lungs and then also to the rest of the body. So humans have a double circulatory system and that means that there are two systems that can be distinguished.
So there's the pulmonary circulatory system which we know relates to the lungs because of that word there pulmonary and then the systemic circulatory system. So systemic means relating to a certain system in this case the body. So the pulmonary circulatory system is when blood flows from the heart to the lungs and then back.
So if we look on this diagram from the heart the blood will go to the lungs and then return back to the heart and then the systemic circulatory system is when blood flows from the heart to the rest of the body and then back. So from the heart to the rest of the body and then back to the heart. Now moving down to this diagram over here, blood enters the heart. When it comes from the superior and inferior vena cava, it enters the right atrium.
From there, it moves into the right ventricle and then the ventricle sends the blood to the pulmonary artery that will go to the left and in the right lung respectively. Now this pulmonary artery will then branch off further and it will eventually form the capillary network that we see here. So in your lungs you have a vast network of capillaries and these capillaries then surround a structure called the alveoli. So the alveoli are these sac-like structures that will become filled with air and that air will then obviously contain oxygen and then it can also be filled with carbon dioxide. So these capillaries surround the alveoli as a net-like structure so that they make very close contact with the alveoli membranes because what's going to happen now is the process of diffusion has to move gases between these two structures.
So if you agree with me now the blood that has gone into the lungs now are deoxygenated and the blood thus has a very low concentration of oxygen but a high concentration of carbon dioxide. In the alveoli there will be a high concentration of oxygen because you've just inhaled air and there'll be a low concentration. of carbon dioxide in the alveoli.
So this will now cause diffusion to happen because diffusion is when something moves from a high concentration to a low concentration. So looking at carbon dioxide first there's a high concentration of carbon dioxide in the blood and now it will move to a low concentration in the alveoli. So that has now moved through the process of diffusion. Now in the lungs, in the alveoli, there's a high concentration of oxygen and there's a low concentration of oxygen in the blood. So the high concentration of oxygen in the alveoli will move into the blood through the process of diffusion.
Now the carbon dioxide that is in the lungs will be exhaled when you breathe out and then the oxygen that is now in the blood is now oxygenated blood and that blood will travel back to the heart. So just looking at another representation here you can just see how close closely the capillaries come to the alveoli they they really are very close to each other so that oxygen can come into the blood and carbon dioxide can go into the alveoli and then the oxygen is sent to the heart and then the carbon dioxide is exhaled. So now that oxygenated blood comes back to the heart through the pulmonary veins and they then enter the left atrium.
From the left atrium it goes to the left ventricle and then from the left ventricle it is pumped to the aorta and the aorta then distributes it to the rest of the body. So that is the pulmonary circulatory system. Now we will look at the systemic circulatory system.
so that is when blood flows from the heart heart to the rest of the body and then back. So looking at this diagram now we've completed the pulmonary circulatory system so the deoxygenated blood has gone to the lungs and it's come back as oxygenated blood it has entered the left ventricle and from there the left ventricle is centered to the aorta which is now distributing it to the rest of the body so this is going to all of your muscles this is going to all of the tissues in your body it's going to all of the organs and the aorta will then eventually branch out and you'll get arterioles and so forth and those arterioles will then further branch out and then it becomes capillaries. So we have a capillary network like this that will then surround the organs and it will go inside the tissues and what the capillaries are now doing is they are going to help slow down the blood so that the process of diffusion can happen so that once again we can switch the gases in the human body. So in the capillaries, you would agree with me that we have now a high concentration of oxygen in the blood and a low concentration of carbon dioxide. In the tissues and in the organs, we will now have a high concentration of carbon dioxide and a low concentration of oxygen.
So there's going to be a gradient that is formed so that the process of diffusion can take place. If you remember from the first video I said the three substances that are transported in the human body is food, so nutrients, oxygen and then carbon dioxide. These two are used to make energy and then another thing that is produced during the process of cellular respiration when energy is made is carbon dioxide.
So these organs and tissues have now all used the nutrients and the oxygen to make energy so now there's a buildup of carbon dioxide in these organs and tissues so now the body needs to get rid of it so that means the high concentration of carbon dioxide in these tissues will move into the capillary network from a high concentration to a low concentration and the oxygen that is in a high concentration in the blood will move to a low concentration in these organs and tissues. So now the blood that was once oxygenated is now deoxygenated because it's got a higher concentration of carbon dioxide. That blood is then pumped back to the heart through the vena cava superior and inferior and then the pulmonary circulatory system will take place again. The oxygen that was now dropped at these organs and tissues will then be used with the nutrients that are carried in the blood to once again produce energy. And once that happens, once again, carbon dioxide will also be produced again.
So those are the two systems in a nutshell. So you can see that they have to, the one can't function without the other. So the systemic circulatory system is basically to the rest of the body. Don't forget the top part as well. So you've also got head and arms at the top that also need oxygen.
So that also forms part of the systemic. the pulmonary is purely just the heart and lungs. I really hope that it makes sense to you now. Please remember to like and subscribe to stay up to date with any new videos that are posted.