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.
Usually heat islands in cities have a mean temperature that is 8 to 10 degrees more than the surrounding rural areas. The temperature difference is greater at night than in the day and larger in winter than in summer.ritten by: sriram balu â¢ edited by: Lamar Stonecypher â¢ updated: 9/19/2010. Heat islands are parts of the urban landscape where there is a steep temperature variation between that area and cooler surrounding areas. There can be a temperature variation as much as ten degrees.