Capillaries and Capillary Beds (Nursing)

00:01 So now let's take a look at the capillary.

00:04 Our capillaries are microscopic vessels with diameters that are so small that the red blood cells have to pass through them in a single fall line.

00:15 Their walls are just a thin tunica intima.

00:19 And in the smallest vessels, only one cell can form the entire circumference.

00:24 So it's like one cell just wraps around itself.

00:29 Capillaries also contain parasites which are spider-shaped stem cells that help stabilize the capillary walls, control permeability, and also play a role and vessel repair.

00:43 Capillary supply almost every tissue except for our cartilage, our epithelia, and the cornea and lens of the eye.

00:52 The function of our capillaries is to exchange gases, nutrients, waste and hormones, between our blood and our interstitial fluid.

01:02 All capillary endothelial cells are joined together by tight junctions, but there are also gaps called intercellular clefts.

01:12 These clefts allow passage of fluids and small solutes out of the capillary into the surrounding interstitium.

01:21 There are three types of capillaries.

01:24 We have continuous capillaries, fenestrated capillaries, and sinusoid capillaries.

01:32 First, the continuous capillaries are going to be found most abundantly in our skin, muscles, lungs and our central nervous system.

01:42 In the central nervous system, the continuous capillaries of the brain are unique.

01:47 This is because they form our blood brain barrier, which are totally enclosed with tight junctions and contain no intercellular clefts.

01:58 The second type of capillary are fenestrated capillaries.

02:02 These are found in areas involved in active filtration such as in the kidneys.

02:07 Also in areas like the intestines where absorption is occurring, and also places where endocrine hormone secretion is occurring.

02:16 The endothelial cells contain a Swiss cheese like look to it with pores called fenestrations.

02:25 These allow for an increase in the permeability of these capillaries, And the fenestrations are also usually covered with a very thin glycoprotein diaphragm.

02:38 The third type of capillary are a sinusoidal capillaries.

02:43 These have fewer tight junctions, and are usually fenestrated with larger intercellular clefts, an incomplete basement membranes.

02:52 These also usually have larger lumens than the other types of capillaries.

02:57 These are found only in the liver, bone marrow, spleen, and adrenal medulla.

03:04 Blood flow in the sinusoidal capillaries is sluggish, which allows time for modification of large molecules and blood cells that pass between the blood and the tissue.

03:17 These also contain macrophages, which are going to capture and destroy foreign invaders.

03:25 So if we look at how our capillaries are arranged in the body, we find that they are arranged in capillary beds or interwoven networks of capillaries between our arterioles and our venules.

03:40 Through these capillary beds, we have microcirculation, which is the flow of blood from the arteriole to the venule through the capillary bed.

03:52 The capillary bed is going to consist of two types of vessels.

03:57 First, you have the vascular shunt which is going to serve as like a big highway or thoroughfare channel between the arteriole and the venule.

04:08 You also have the true capillaries, which are going to be the actual vessels that are going to be involved in exchange of nutrients and oxygen.

04:18 So taking a closer look at the vascular shunt, we find that the metarteriole thoroughfare channel is going to start at the terminal arteriole that will then feed into the metarteriole, which is going to be intermediate between the arteriole and the capillary.

04:36 This is also going to be continuous with the thoroughfare channel, which then feeds into the postcapillary venule that will then drain the bed and then send the blood back toward the heart.

04:51 The other part of the capillary bed is the true capillaries were exchanged between vessels and tissues is going to take place.

04:59 There are 10 to 100 exchange vessels per capillary bed.

05:04 These are going to branch off of the metarteriole or the terminal arteriole.

05:10 And the true capillaries are going to normally branch from the metarteriole and then return to the thoroughfare channel.

05:19 Also, our true capillaries contain precapillary sphincters which are going to be responsible for regulating blood flow into the true capillaries.

05:30 These are going to determine whether blood may go into the true capillary or go to the shunt.

05:37 This is going to be regulated by local chemical conditions and vasomotor nerves.