Browse the corpus

Blood vessels are fundamental components of the cardiovascular system, responsible for the dynamic transportation of matter and blood products to every cell in the body. The vascular network begins at the outlets of the heart, courses the entire body, and returns at the major venous inlets of the heart. This complex vascular highway functions to deliver blood cells, nutrients, oxygen, and pharmacological agents to tissue. Just as blood vessels direct material towards the tissue, they also facilitate the removal of cellular byproducts, carbon dioxide, and toxic chemicals from the tissue. Histologically the vasculature system is separated into macro vasculature and microvasculature. The macro vasculature being any vessel observable with the naked eye, and the microvasculature being vessels that are less than 100 microns.

The vast network of blood vessels is involved either directly or indirectly in many pathological disease states. The most common of which is atherosclerotic disease. This pathology begins with low-density lipoprotein (LDL) being taken up by the endothelial cells of vessels. As LDL begins to accumulate in the intima, macrophages work to digest the oxidized it. When the LDL is present in the intima in excessive amounts, the macrophages become overwhelmed and turn into foam cells. A ‘Fatty streak,’ composed of these foam cells, begins to form in the subendothelial space between within the tunica intima. The smooth muscle cells in the tunica media being to proliferate due to inflammatory cytokine signaling and secrete fibrous cap that entombs to fatty streak. The risk of such changes to the vascular wall includes thrombotic events, embolic events, and restriction of flow, which progresses in severe cases to occlusion of flow. In some instances, these fatty streaks can be so impressive that they are visible with the naked eye on a gross specimen.[14][15] Cytokine response to stress or inflammation will cause separation of the endothelial lining of the vessel, which allows fluid extravasation into the surrounding tissue. These cytokines induce endothelial cell retraction, allowing otherwise impermeable large molecules, to pour out into the surrounding extravascular space. Similar changes within this functional array of hyperpermeability, angiogenic growth, and endothelial proliferation carries implications in angiomas and angiosarcomas.[16] Diabetic neuropathy is thought to be secondary to sclerotic changes and increased resistance in the small blood vessels that supply the peripheral nerves, the nervi vasorum.[17] On histology, myocardial fibers are sometimes visible, extending into the pulmonary veins and vena cava walls. These continuations of myocardial tissue into the vessel wall are what are known as myocardial sleeves and are possible foci for the generation of atrial fibrillation.[18]