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Research centering on blood flow in the heart continues to hold an important position, especially since a better understanding of the subject may help reduce the incidence of coronary arterial disease and heart attacks. This book summarizes recent advances in the field; it is the product of fruitful cooperation among international scientists who met in Japan in May, 1990 to discuss the regulation of coronary blood flow.
Writing critically about something you have come to regard with affection must provoke mixed emotions. As I learned more and more about the modern battleship's shortcomings, I found myself, like so many before me, falling under its spell. I have traveled hundreds of miles to visit these wonderful ships, reverently preserved like a necklace of talismans around our nation's coasts. I have stood in awe under the great guns, wondering what it must have been like to hear them fire. Perhaps it is true that their sound and fury signified very little in terms of actual destructive power. But most people thought they did, and that was and still is important. Besides, for the most part, we were proud of those ships. Now we live in a time of weapons so terrible that we must actually hide them-beneath the ground and below the surface of the sea. But, like battleships, they keep the peace precisely because of what others think they can do. All things being equal, who would not prefer the dreadnoughts?
This e-book will review special features of the cerebral circulation and how they contribute to the physiology of the brain. It describes structural and functional properties of the cerebral circulation that are unique to the brain, an organ with high metabolic demands and the need for tight water and ion homeostasis. Autoregulation is pronounced in the brain, with myogenic, metabolic and neurogenic mechanisms contributing to maintain relatively constant blood flow during both increases and decreases in pressure. In addition, unlike peripheral organs where the majority of vascular resistance resides in small arteries and arterioles, large extracranial and intracranial arteries contribute significantly to vascular resistance in the brain. The prominent role of large arteries in cerebrovascular resistance helps maintain blood flow and protect downstream vessels during changes in perfusion pressure. The cerebral endothelium is also unique in that its barrier properties are in some way more like epithelium than endothelium in the periphery. The cerebral endothelium, known as the blood-brain barrier, has specialized tight junctions that do not allow ions to pass freely and has very low hydraulic conductivity and transcellular transport. This special configuration modifies Starling's forces in the brain microcirculation such that ions retained in the vascular lumen oppose water movement due to hydrostatic pressure. Tight water regulation is necessary in the brain because it has limited capacity for expansion within the skull. Increased intracranial pressure due to vasogenic edema can cause severe neurologic complications and death.
This report considers the biological and behavioral mechanisms that may underlie the pathogenicity of tobacco smoke. Many Surgeon General's reports have considered research findings on mechanisms in assessing the biological plausibility of associations observed in epidemiologic studies. Mechanisms of disease are important because they may provide plausibility, which is one of the guideline criteria for assessing evidence on causation. This report specifically reviews the evidence on the potential mechanisms by which smoking causes diseases and considers whether a mechanism is likely to be operative in the production of human disease by tobacco smoke. This evidence is relevant to understanding how smoking causes disease, to identifying those who may be particularly susceptible, and to assessing the potential risks of tobacco products.

NOAA.

United States. National Oceanic and Atmospheric Administration

Published: 1980

Total Pages: 512


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An alphabetical arrangement of the ships of the continental and United States Navies, with a historical sketch of each one.