Blood Vessels: Structures and Functions (Nursing)

00:01 Welcome.

00:01 In this lecture, we will be discussing the blood vessels.

00:06 So first, blood vessels are the delivery system of dynamic structures that begins and ends at the heart.

00:15 Our blood vessels work with our lymphatic system in order to circulate fluids.

00:22 The blood vessels include the veins, which are going to carry blood toward the heart, and are mostly deoxygenated with the exception of our pulmonary circulation and the umbilical vessels of the fetus.

00:36 The second vessel are our arteries.

00:38 This carries blood away from the heart, and it's usually oxygenated except for in pulmonary circulation, and the umbilical vessels of the fetus.

00:49 Finally, we have our capillaries.

00:52 These are going to be vessels that come in direct contact with our tissue cells and are going to directly serve our cellular needs.

01:02 So if we look at the structure of our blood vessels, we find that all vessels consist of a lumen, which is the central blood containing space surrounded by a wall.

01:15 The walls of all of our vessels are going to have three layers or tunics.

01:20 Starting on the inside, we have the tunica intima, followed by the tunica media, and the outermost layer being the tunica externa.

01:30 Our capillaries are a little different, and that they do not have these three layers.

01:36 Instead, our capillaries are just made up of an endothelial layer and a sparse basal lamina surrounding it.

01:45 So if we take a closer look at each of the layers, we find that the tunica intima is going to be our innermost layer and it's going to make intimate contact with our blood.

01:57 It is composed of an endothelium which are simple squamous epithelial cells that line the lumen of the vessel.

02:06 It is going to be continuous with the endocardium of the heart and has a very slick surface that reduces friction as blood flows through the vessel.

02:19 There is also a subendothelial layer in this tunica, which is going to be made up of connected tissue basement membrane.

02:28 But this is actually only found in some of the larger vessels.

02:34 The next layer or the middle layer is our tunica media.

02:39 This is going to be composed of mostly smooth muscle tissue and sheets of elastin.

02:46 This is going to have sympathetic vasomotor nerve cells also within this layer, which are going to control vasoconstriction, which leads to a decrease in our lumen diameter or vasodilation, which was to an increase in the diameter of the lumen.

03:05 This is our bulkiest layer and it's going to be responsible for maintaining blood flow as well as blood pressure throughout the body.

03:14 The third layer and outermost layer is our tunica externa.

03:19 This is sometimes also called the tunica adventitia.

03:24 It's going to be composed mostly of loose collagen fibers that are going to protect and reinforce the wall as well as anchor the vessels to its surrounding structures.

03:37 This is also infiltrated with nerve fibers as well as lymphatic vessels.

03:43 Also, large veins contain elastic fibers in this layer.

03:49 Also, within this layer, we have the vasa vasorum or a system of tiny blood vessels that are going to be found in our larger vessels.

03:58 This is going to function to nourish this outermost layer of our blood vessels.

04:06 So if we look at the structure of the blood vessels, to recap, the blood vessels in the body have three layers.

04:14 They're going to be the tunica intima, which is the innermost layer.

04:18 the tunica media, which is the middle layer.

04:21 and the tunica externa, which is the outer layer.

04:25 Also our blood capillaries, which are going to be the smallest of our vessels are going to just consist of an endothelial layer surrounded by a loose basal lamina.