Lymphatic Vessels – Introduction to the Cardiovascular System

00:00 The lymphatic vessels are an extensive network of vessels and they are in the sense the ultimate in terms of drainage. A small amount of fluid leaks out of the capillaries as we will talk about later and the lymphatic vessels make sure that this fluid doesn't collect in the space between the cells known as the interstitial space but is eventually collected in the lymphatic vessels and brought all the way back into the chest and into the venous system where that fluid then becomes part of the blood and gets into the circulation again so that we don’t develop swelling or edema in the peripheral tissues. We will have much more to say about the lymphatic system later but just to say the lymphatic system is not just a series of small vessels that drains excess fluid in the tissues but it also is connected to lymph nodes that are scattered throughout the body as well as the thymus gland in the neck and the spleen in the abdomen and each of these components plays a major role in the immunological systems, that is the defense system against bacteria and viruses. And of course there are the small vessels as we mentioned before. Functions as I have also mentioned is to return any excess body fluid that leaks out into the tissues back to the circulation.

01:27 It transports also interestingly enough, fats from the intestines to the blood so that these substances can be brought to the liver for further digestion and distribution as nourishment to the cells.

01:40 And finally, as I mentioned before, part of the defense system, part of the major immunological defense system that defends our body against infections of a variety of kinds. Let's look here at the other component of the cardiovascular system that is the blood vessels themselves.

01:58 As you see, they start with large arteries that branch down to smaller and smaller arteries and eventually to the arterioles which as I mentioned before is the major source of resistance in this circuit. Then following the arterioles are the capillaries, that is where the oxygen is delivered to cells and nutrients are delivered to cells and waste products such as carbon dioxide are removed from the cells. The blood then passes into the venules, very small veins, and eventually to larger veins and as we have said, returns to the heart to start the circuit all over again with supplying of oxygen in the lungs and loss of carbon dioxide to the atmosphere. Here again a little more detail of the various blood vessels. The arteries convey blood away from the heart to the body tissues. They bifurcate, that is they divide, into smaller and smaller vessels eventually reaching the arterioles which are the smallest part of the arterial system and that is where the resistance in the system lies as I have said before and then the arterioles connect to the capillaries which are in intimate connection with the cells of the body allowing exchange of oxygen, carbon dioxide, nutrients and waste products as I mentioned before. Then the blood goes into small venules and to progressively larger veins and eventually returns to the right side of the heart to go to the lungs. Here we see in a very nice cartoon the arteriole system coming out of the left side of the heart, branching down to the arterioles, then into the capillaries, returning from the capillaries into venules, and then into larger veins, and then returning to the right side of the heart in a continuous circle.

03:50 Now interestingly enough, both within the arteries and within the veins, there are some connections between arteries and arteries and veins and veins. These are called anastomoses which means connecting mouths, and this happens where anytime there are two or more vessels that merge to supply the same body region. This is in a sense, if you will, a reserve system so that if one of these arteries become blocked, blood will get into the system through the anastomosis and through the sister artery that is still there, and veins actually have even more anastomoses so that if one of the veins closes down in fact the blood will move through the anastomosis into another vein and still get to return from the body. In a sense it's a reserve system in case one of the arteries or veins closes down.