Therapeutic concepts in oncology such as antiangiogenic or antivascular approaches have reawakened the scientific community's interest in comparative microvascular anatomy and biology. Microvascularity and angiogenesis play a significant role during normal growth, in physiological conditions, and in a variety of pathological conditions such as inflammation, diabetes, macular degeneration, and wound healing. Angiogenesis is thus, not a specific phenomenon in tumors, but instead an integral element of numerous different normal and pathological conditions.
After the short early embryonic phase of primary angio-genesis, which comprises the formation of poorly differentiated vessels composed of endothelial cells derived from angioblasts of blood islands in the extraembryonal mesoderm of the yolk sac, all further vascular growth in physiological and pathological conditions is summarized as secondary angiogenesis. In secondary angiogenesis formation of new vessel segments can be accomplished either by vessel sprouting, which requires endothelial cell mitoses, or by intussusceptive growth without need for endothelial cell mitoses. Primary angiogenesis never works without mitoses.
When describing microvessel morphology, we have to discern between structure and architecture, both of which determine functional properties in terms of blood flow. Structure in morphological terms means vessel wall building, cellular differentiation, cell shape, cell contact structure and cell surface differentiation, and organelle and cytoskele-ton contents. Microvessel architecture encompasses pattern formation, vessel course, density, and all parameters defining the 3D arrangement of the microvascular unit.
Microvessel architecture can be studied best by means of scanning electron microscopy of corrosion casts, which allows also for 3D imaging, reconstruction, and quantitative analysis. For microvascular corrosion casting a resin is injected into the vascularity either systemically or locally. After polymerization of the casting medium the tissue is corroded in an alkaline solution. After drying and mounting the vessel system replicas can be studied in detail. Intravital microscopy, especially after injection of fluorescent dyes, is effective in the observation of two-dimensional vascular networks as given in most angiogenesis assay systems. The possibility of examining the vasculature in the time course is the biggest advantage; the limited resolution the major shortcoming. Classical injection methods with light microscopic evaluation are time consuming, require laborious reconstruction work, and are still of limited value, unless sophisticated computerized techniques are used. The variety of morphological techniques for assessing microvascular structure from light to confocal scanning and transmission microscopy was increased significantly by immunostaining, allowing for further structure-function correlations.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.