Angiogenesis: Biology and Pathology, Second Edition.

During development, the first blood vessels are formed by the de novo assembly of angioblasts, endothelial cell precursors, in a process called vasculogenesis. All subsequent sprouting of blood vessels from pre-existing vessels is termed angiogenesis and is a process that continues throughout our lifespan during physiological processes such as wound healing as well as in number of pathological conditions, such as tumor growth and age-related macular degeneration. The circulatory system pumps blood from the heart out to the organs through arteries and deliveries oxygen and nutrients via capillaries to tissues and cells and returns carbon dioxide and waste products back through veins. Each organ varies in its blood vessel patterning, reflecting specialization to accomplish diverse functions including vascular permeability, filtration, immune trafficking, and hormone regulation. Approximately 90% of the fluid extravasated into the interstitium is recycled back to the circulatory system via the unidirectional lymphatic system. Lymphatic capillaries drain fluid, proteins, and cells from tissues and transport this lymph fluid through collecting lymphatic ducts toward lymph nodes. Eventually lymphatic fluid from the right and left lymphatic ducts joins the subclavian veins and recirculates throughout the circulatory system. These two intricate vascular systems, working in cooperation, help to maintain essential bodily functions such as fluid dynamics, tissue homeostasis, blood pressure, metabolism, and immunity. However, dysfunction of these systems is associated with a host of pathological conditions, including cardiovascular diseases, obesity, retinopathy, hypoxia, necrosis, and vascular malformations.