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6. Blood Vessels.pdf

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Anatomy & Cell Biology
ANAT 261
Craig Mandato

Naveen Sooknanan McGill Fall 2011 Blood Vessels: Up until now, we have learned specific tissues which are the building blocks of larger structures. The first one we will learn about is blood vessels The circulatory system consists of the heart, whose function is to pump blood, and the vascular system, containing afferent and efferent blood vessels Efferent vessels are the arteries, which leave the heart and bring oxygen and nutrients to all tissues through a capillary network Afferent vessels are veins, which come back to the heart, carrying in the carbon dioxide and waste products from all tissues through the convergence of the capillary system larger vessels As can be seen by this plan, for each efferent vessel there is a corresponding afferent vessel o In cross section, you will be able to see there 2 vessels running in parallel o In longitudinal section, you will only see one vessel, because the plane of section removes the parallel vessel from sight The lymphatic vascular system is an anastomic network of vessels closely related to the vascular system Lymphatic vessels behind as blind (one ended) capillaries which converge into lymphatic vessels, and then into lymphatic ducts These lymphatic ducts drain into large veins These vessels contain lymph which is plasma enriches in immunoglobulins and lymphocytes produced by lymphatic organs We do not need to identify any of these vessels in the lab, because they can easily be confused with capillaries and venules The following is a general structure of a blood vessel. Note that not all of the vessels will contain every component mentioned in here (in fact, only one of them does). This is just a list of everything we can encounter in a blood vessel The intima is the innermost later (closest to the lumen) o The endothelium (epithelium for blood vessels) is a simple squamous epithelium Locating this helps you identify the rest of the layers There are tight and gap junctions in this epithelium o The sub-endothelial layer contains ECM, just fibers, no cells This is a remnant of CT Very thin CT, usually very hard to identify and sometimes absent o Within the sub-endothelial layer is the internal elastic limiting membrane (IELM) It is very acidophilic, it stains pink or dark red It has a wavy structure because it retracts during fixation In vivo, it would be smooth 1 Naveen Sooknanan McGill Fall 2011 The IELM is synthesized by SMCs, which some people think should make it part of the media (the next layer) For us, its part of the intima It is made up of elastic fibers The next layer is the media, which is a midlayer containing SMCs o The media also contains proteoglycans and reticular fibers (type III collagen) o The thickness of the media is different depending on the type of vessel The adventitia surrounds the media and is the outermost layer of the blood vessel (BV) o It is made up of dense irregular CT which contains type I collagen o The adventitia also contains smaller blood vessel which provide nutrients to the wall of the larger blood vessel. This is known as vasa vasorum Only found in large BVs As the media thickens, oxygen and nutrients cannot diffuse through the wall, so they need the help of smaller BVs Whenever you get a cross section of a BV, you must be able to identify both corresponding BVs (afferent and efferent) as they will likely be in the same section. We will learn tricks on how to differentiate between corresponding BVs as well as different BVs of the same class Elastic artery with large vein Muscular artery with medium of small vein Arteriole with venules Capillaries all look the same (cant differentiate) Elastic arteries and large venules are directly related to the heart. First, lets look at elastic arteries: There are multiple elastic membranes in an elastic artery. Only the FIRST one is called the IELM and divided the intima and media The media consists of cocentric elastic membranes and SMCs, which are in all directions o Typically, SMCs run around the circumference of BVs, but not here Elastic arteries include the aorta and carotid arteries Zooming into the media, we see that cytoplasmic projections of the SMCs almost touch the EMs o Intermediate filaments in SMCs are normally desmin, whereas in epithelial tissue, these filaments 2Naveen Sooknanan McGill Fall 2011 are vimentin o However, in elastic arteries, the intermediate filaments are vimentin (exception) Also, in between EMs, there is a lot of reticular fibers (type III collagen) o The EMs are also fenestrated, meaning they have tons of perforations, or windows Mutations can cause 2 mains diseases: o Aneurysms are caused by Ehlers Danlos disease, which ruptures BVs o Atherosclerosis happens when you have high cholesterol Foam cells, a type of macrophage, invade the intima and media The intima gets pushed into the lumen, which blocks off the BV (occlusion) and can cause a heart attack The adventitia is a large area of dense irregular CT o Vasa vasorum can be observed SMCs Endothelium IELM
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