Embryo Project Encyclopedia

In nineteenth century Great Britain, Thomas Henry Huxley proposed connections between the development of organisms and their evolutionary histories, critiqued previously held concepts of homology, and promoted Charles Darwin's theory of evolution. Many called him Darwin's Bulldog. Huxley helped professionalize and redefine British science. He wrote about philosophy, religion, and social issues, and researched and theorized in many biological fields. Huxley made several methodological contributions to both invertebrate and vertebrate embryology and development, and he helped shape the extra-scientific discourse for these fields.

Johann Friedrich Meckel studied abnormal animal and human anatomy in nineteenth century Germany in an attempt to explain embryological development. During Meckel's lifetime he catalogued embryonic malformations in multiple treatises. Meckel's focus on malformations led him to develop concepts like primary and secondary malformations, atavism, and recapitulation- all of which influenced the fields of medicine and embryology during the nineteenth and twentieth centuries.

The endothelium is the layer of cells lining the blood vessels in animals. It weighs more than one kilogram in adult humans, and it covers a surface area of 4000 to 7000 square meters. The endothelium is the cellular interface between the circulating blood and underlying tissue. As the medium between these two sets of tissues, endothelium is part of many normal and disease processes throughout the body. The endothelium responds to signals from its surrounding environment to help regulate functions like the resistance that blood vessels need to pump blood through the body (vasomotor tone), the policing of substances trying to enter or exit the blood vessel (blood vessel permeability), and the ability of blood to clot (hemostasis). In addition to diseases like atherosclerosis, endothelium has been indicated as a component in pathologies like cancer, asthma, diabetes, hepatitis, multiple sclerosis, and sepsis. The shape, size, and appearance of endothelial cells, called their phenotypes, vary depending upon which part of the body the cells are from, a property called phenotypic heterogeneity. The endothelium, its properties, and its responses to stimuli are governed largely by the local environment of the cells.