 Now, we compare briefly the veins and arteries and capillaries, veins faces minimum pressure at least in major veins the pressure is almost negligible. Vains have to collect blood from the body and return it to the heart. They also have to flow against the gravitational pull and this is very important. Number one they have less pressure, reduced pressure, secondly they are returning blood may be from the legs, from the feet to the heart. They are moving, the blood is moving, the blood flow is against the gravitational pull. So, there is a more problem in movement of blood through the vessels toward heart. The arteries faces maximum pressure, they have to distribute blood. Blood is pumped by the heart, so it is having high pressure, so they are thick walled and veins are involved. Vains don't need any walls, veins need walls to regulate the blood flow. Capillaries have to exchange materials with the tissues, so they are simply one cell thick and very very small. Now, we look at the importance of walls in the veins. Let us have a look on the diagram. In the center a vein is shown, most of the major veins, the larger veins have walls inside because pressure is reduced. For example, from our leg towards our heart, when blood is flowing with low pressure and with the wider lumen of the vein, there is a problem in returning that. How it occur? Our muscles, group of muscles help them. There are groups of muscles surrounding these veins which contract and relax at intervals to push the blood towards the heart. Now when a group of muscles contract, blood goes up but because pressure is low, when the muscles relax, it could flow back. These walls stop that back flow. When a group of muscles contract, blood goes up, then walls are open and allow the blood to go up. When the muscles relax, these walls closes. When they closes, they prevent the back flow of the blood downwards. Then comes the next walls and the next set of muscles which contracts and the blood goes from that portion to the next portion and then its walls also close. This process continues until the blood reaches heart and in an abdominal area where there are larger veins, very large veins, the movement of our abdomen and the thorax due to the respiratory movements also help pushing this blood towards the heart to the inferior vena keva which is a major vein which is returning blood to the heart. This was the importance of these walls present inside the veins. They actually stop the back flow of blood inside the vein. Now we are going to talk about the main arteries and veins inside the human arterial and venous. In human arterial and venous system, there are a lot many arteries, veins, capillaries. We will talk about only the major ones. Let us have a look on a diagram. The diagram in front of you is showing you the major circulatory vessels inside a human body. The diagram, if we divide this diagram and the vessels into two major parts, then it will be easier to understand. We can see in the red all the arteries because the arteries have oxygenated blood. We can simply say the veins are in blue because veins have deoxygenated blood. We start with the arteries. Arteries as you can observe here that from the heart, one major artery is arising. This is called aorta, aortic artery. This aorta just going ahead and making an arch, we call it aortic arch. When blood is pushed by the heart, it is pushed into the aorta to send it towards the body. From aorta, we can see that on the top, various branches are arising. These branches are giving blood to the head and neck region and also to the shoulders and the arms. You can see on the top, two major arteries going towards the head and neck called carotids. Carotids arteries are taking blood from the aorta and giving it to the head and neck region. Then you can see the subclavian artery. Subclavian artery is giving blood to the shoulders and then it is going towards arms to make the brachial artery. The brachial artery is giving blood to the arms. Then this is the head, neck and shoulders and arms. Now we go down. The aortic arch goes down by turning downwards and making a very large vessel down there. It runs actually towards the dorsal side of the body. So we call it dorsal aorta. Dorsal aorta distribute blood to all the other organs of the body. This is other than head, neck, shoulders and arms. As you can see, just below the heart, this artery is giving a brach to the liver. This is called hepatic artery. Hepatic is something related to liver. Then on the other side, just some way down, it is giving an artery to the kidneys. This is called renal artery. Renal means something related to kidney. That is renal artery, artery going towards kidneys. Slightly goes down. We can see that there is an artery going towards the gonads. It is called gonadal artery. Going something more down, there is an artery called celiac artery, which is divided into more branches and a bisenteric artery. These arteries are giving blood to the digestive system organs, the intestine, the stomach. This is also giving blood to the mis entries, the membranes which are present inside the abdominal cavity. Then this is going down. The dorsal aorta is divided into two major vessels called the iliacs. Iliac arteries are giving blood towards the legs. This artery is further going down to make the femoral arteries. Immoral arteries give blood to the lower parts of the leg. That is D, calf and the foot. Now we talk about the veins. Vins have to return blood to the heart. We again divided into two parts from the upper parts of the body, the head, neck and shoulders and arms, and the lower part of the body, legs and the lower organs. From the head, you can see that there is a jugular vein. We call it jugular vein, which is returning blood from the head and neck region to the major vessel. Actually there are two major veins which are returning blood to the heart. One is called superior vena keva and the other is called inferior vena keva. Superior vena keva is returning blood from the head, neck, shoulders and arms back to the heart. While inferior vena keva, as you can see in the diagram, this is taking blood from all the other organs, the lower organs and the legs, and giving this blood to the heart. Superior vena keva receives the jugular vein from the head and neck, receives the subclavian vein from the arms and the shoulders, and if we go down to the inferior vena keva, then it is receiving a vein from the liver, a hepatic vein, from the gonads, the gonadal veins, the iliac veins and then femoral veins from the knee, calf and feet and the iliac veins towards from the legs. These are the major, major blood vessels of a human circulatory system. I simply say aorta which is the major vessel, the major artery, which is receiving blood directly from the heart and sending it towards the body and the superior and inferior vena keva which are returning blood from the body towards the heart. And then aorta makes branches towards the head, neck and shoulders and arms and then it gives away lower branches towards the visceral organs of the body and to the legs. And superior vena keva receives blood from head, neck, arms and shoulders and inferior vena keva receives blood from all the other organs. Heart itself have circulation which is called coronary circulation. Heart also receives arteries which have to give blood or of course distribute nutrients and oxygen and everything to the tissues of the heart itself. These are called coronary arteries. Then these distribute and converted to coronary veins and then gives back to the give back blood to the vena keva. These coronary arteries and veins are very important because if sometimes any coronary artery or veins, arteries particularly is blocked then the result may be a quick death of the tissues of the heart which may result in a myocardial infarction. That is serious disease which may causes even death of the patient. So, these were the major arteries and veins of the human circulatory system. One thing more that there is only one artery and there is only one vein which have opposite to the normal oxygenary and deoxygenated situation. The pulmonary vein actually have oxygenated blood because it is coming from the lungs back to the heart and the pulmonary artery have the deoxygenated blood because it is actually taking blood from the heart and giving it to the lungs. So, we can say that there is only one artery pulmonary artery which have deoxygenated blood and there is only one vein the pulmonary vein which have oxygenated blood opposite to the normal situation. That is arteries have oxygenated blood and the veins have deoxygenated blood.