The Vascular System
Highlights
- The clinical landscape of atherosclerosis is currently changing with the use of plaque stabilizing drugs leading paradoxically to more complications from plaque erosion and the recognition of new emerging risk factors. (View Highlight)
- Peripheral vascular disease has 2 clinical causes: primary atherosclerosis in large vessels and chronic thrombi in smaller vessels. Medial wall calcification contributes to thrombus formation in smaller vessels (View Highlight)
- It wasn’t until William Harvey’s An Anatomical Exercise on the Motion of the Heart and Blood in Living Beings publication in 1628 that the circulation was understood to be a closed loop system originating and terminating in the heart (View Highlight)
- The arterial system consists of 8 branching segments proximal to the capillary system.3 However, functionally there are only 3 relevant categories of vessels in the arterial system; large conduit arteries (diameter>300 μm), resistance arteries (diameter 50–300 μm), and arterioles (diameter 10–50 μm). (View Highlight)
- All vessels consist of 3 layers; the interna (or intima), the media, and the adventitia4 (View Highlight)
- The interna consists of the endothelium, which is semipermeable and whose endothelial cells [EC] synthesizes various “paracrine” vasoactive agents,5, 6, 7 and the internal elastic lamina which separates the endothelium from the media. The latter functions as a fenestrated barrier allowing various cells and substances passage between layers (View Highlight)
- The media contains transversely arranged vascular smooth muscle cells (VSMC) that mediate vascular tone and a matrix of collagen and elastic lamellae.9 Tone and caliber are modulated by the neurotransmitter activation of subunit receptors.10 The media changes in size and content with the branching of the arterial system, in proximal branches elastin predominates and in the terminal conduit arteries VSMC predominates.11 In resistance arteries and arterioles the media has progressively less VSMC before transitioning to the capillary system (View Highlight)
- The external elastic lamina resides between media and adventitia. The adventitia is the outermost layer and is comprised of collagen, elastin, and fibroblasts. This outer layer protects the artery from damage.4 The vasa vasorum (blood vessels that supply blood vessels) and nerves that innervate the media reside within the adventitia (View Highlight)
(View Highlight)