As part of an immune response to foreign pathogens, histamine is produced by basophils and by mast cells found in nearby connective tissues. Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues.
Where vegetation is sparse, temperature is hot. (Image: NASA) An urban heat island (UHI) is a metropolitan area which is significantly warmer than its surroundings. According to the EPA, many U.S. cities have air temperatures up to 10Â°F (5.6Â°C) warmer than the surrounding natural land cover.
What are Heat Islands? An island is a piece of land surrounded on all sides by water. So what are heat islands? These are a particular part of land where there is a steep temperature variation between this part and its surrounding land. Usually heat islands in cities have a mean temperature that is 8 to 10 degrees more than the surrounding rural areas.