So now that we've talked about the general structure of capillary beds in our previous lesson videos, in this video, we're going to focus on the structure of mesenteric capillary beds. The mesenteries are the serous membranes of the digestive system that hold our intestines in place. These mesenteries have a specialized capillary bed structure that includes the presence of a vascular shunt, which is important for the precise and fine-tuned control of blood flow through the capillary bed. Let's take a look at our image down below so that we can visualize this vascular shunt. Notice on the left over here, we're showing you the capillary bed structure of the mesenteries, which looks very similar to the capillary beds that we showed you in our previous lesson videos. However, notice that it has this structure that we are highlighting here in green and zooming into up above so that you can see the details more clearly. This is the vascular shunt. The vascular shunt allows for blood to be shunted or for blood to pass directly from the terminal arteriole through to the postcapillary venule. This vascular shunt actually consists of 2 parts. The first part is the metarteriole, and the second part is the thoroughfare channel. The first part of the vascular shunt is the metarteriole, highlighted here and bracketed is the metarteriole, and then the thoroughfare channel is going to be the remainder of the vascular shunt. The metarteriole is a transitional blood vessel because it has intermediate characteristics of an arterial and a capillary. The most key defining feature of these metarterioles is that they contain what are known as precapillary sphincters on its branches into the capillary bed network. These precapillary sphincters are smooth muscle rings that act as valves or blood flow control into the capillary bed network. So taking a look at our image down below, notice that the precapillary sphincters are being circled with these dotted circles that you see here. Again, these are rings of smooth muscle that wrap around the branches of the metarteriole into the capillary bed network. When these precapillary sphincters contract, they narrow down the branch here and prevent blood from flowing into the capillary bed, and so that redirects the blood flow further into the vascular shunt. The second part of the vascular shunt is the thoroughfare channel, and the thoroughfare channel is really just the continuation of the metarteriole. But the biggest difference is that the thoroughfare channel lacks smooth muscle, including the precapillary sphincters. As soon as the metarteriole loses its precapillary sphincters, it then is considered the thoroughfare channel. The thoroughfare channel will directly connect the metarteriole to the postcapillary venule. The reason that this vascular shunt is so important is because it allows for the precise and fine-tuned control of blood flow through the capillary bed, and that's exactly what the image on the right is focusing on. Notice that the image at the top right up here is focusing in on the vasoconstriction of just the arteriole and the terminal arteriole, just like what we saw in previous lesson videos. Notice that the vasoconstriction of the arteriole is being indicated by these yellow arrows highlighted here, and the vasoconstriction of the terminal arteriole is being indicated by those yellow arrows that you see highlighted right there. The vasoconstriction is going to reduce blood into the arteriole, reduce blood flow into the entire capillary network and vascular shunt, and it's going to redirect blood flow in other areas of the body, very similar to how we saw blood flow redirected in our previous lesson videos. In this top image, it's really nothing new. It's very similar to what we saw in our previous lesson videos, where the blood flow is
Table of contents
- 1. Introduction to Anatomy & Physiology5h 40m
- What is Anatomy & Physiology?20m
- Levels of Organization13m
- Variation in Anatomy & Physiology12m
- Introduction to Organ Systems27m
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- 19. The Blood Vessels3h 35m
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- 25. The Urinary System2h 39m
- 26. Fluid and Electrolyte Balance, Acid Base Balance Coming soon
- 27. The Reproductive System2h 5m
- 28. Human Development1h 21m
- 29. Heredity Coming soon
19. The Blood Vessels
Capillaries
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