Veins (Nursing)

00:01 So now let's take a look at another type of vessel the veins.

00:05 The veins are going to carry blood toward the heart.

00:09 Their formation begins at the capillary beds, when they unite into the postcapillary venules and then merge into larger and larger veins.

00:20 The smallest of the types of veins is going to be the venule.

00:25 Recall that the capillaries are going to unite to form postcapillary venules.

00:31 These are going to consist of an endothelium of surrounded by a few parasites.

00:38 These are very porous and allow fluids and white blood cells into the tissues.

00:44 The larger venules also have one or two layers of smooth muscle cells.

00:51 From the venules, we have veins.

00:54 These form when the venules converge.

00:58 These are going to have all three tunics but they're going to have thinner walls with larger lumens compared to the corresponding arteries.

01:07 The tunica media of our veins is thin, but the tunica externa of the veins is thick.

01:14 These are going to contain collagen fibers and elastic networks.

01:19 Veins contain a large lumen and thin walls which make the veins good storage vessels.

01:27 They are called capacitance vessels or blood reservoirs because they contain up to 65% of our blood supply.

01:38 So in this histology section, notice the physical differences between the arteries and the veins.

01:44 While the arteries have thicker walls, the veins have much larger lumens.

01:49 And at the tunic level, you can see that the tunica media of the arteries is thicker than in the veins, but the tunica externa and the veins is much thicker than in the arteries.

02:02 Veins are low resistance vessels.

02:05 So blood pressure is lower than in the arteries.

02:08 So adaptations in the veins ensure the return of blood to the heart.

02:14 The large diameter lumens of the veins offer little resistance.

02:19 One venus adaptation are the venus valves.

02:23 These are folds of the tunica intima that formed flap light cusps that prevent backflow of blood.

02:32 These are going to be most abundant in the veins of our limbs.

02:37 Another adaptation in veins are the venous sinuses.

02:42 They are flattened veins with extremely thin walls.

02:46 They are comprised of only endothelium and do not have smooth muscle.

02:52 Examples of venous sinuses include our coronary sinus of the heart, as well as the dural sinuses of the brain.

03:01 So to recap, notice the difference between the arteries and the veins.

03:06 Notice the difference in the lumen size with the veins having the larger lumen also noticed the difference in the thickness of the tunica media and externa between the two.

03:19 Also, you'll notice how the veins contain valves which are going to be important for the prevention of backflow of blood.

03:28 Also notice a difference between our capillaries and the other vessels, including their smaller diameter and the presence of fenestrations.