 Dear students, in this topic we shall discuss endothermia in hot environments. Dear students, the major problem of the endotherms living in hot environments is the dissipation of body heat. Endotherms have evolved mechanisms to lose body heat. The body heat is always lost from the body surface. Blood vessels carrying blood to the surface regulate the rate of heat loss. Dear students, the various mechanisms used to dissipate or lose heat from the body surface include the use of various types of heat windows, evaporative heat loss and behavioral and postural changes. We shall discuss these mechanisms one by one. First we are going to discuss the heat windows. Endotherms have made different types of heat windows on their body surface. In heat windows openings or closings, regulation of blood flow or in heat windows openings or closings are regulated by blood flow. Heat loss mechanisms used by the body surface include radiation, conduction and convection. Radiation is to lose heat in the air. Conduction is to transfer heat from one surface to another, i.e. from hotter surface to warmer surface. We shall take a few examples of these heat windows. First example of heat window is the ears. Ears of many mammals are thin, large, membranous and very lightly fared. They are also supplied extensively with blood vessels. So these features act as temperature regulators and so the ears act as temperature regulating windows. The second example of window is the horns. Horns of many mammals, for example, goats and cattle are highly vascularized. The blood vessels in them vasodilate under conditions of heat load. As a result, heat is radiated. The third example of heat window present in many mammals is the limbs and snouts. They have large surface to volume ratios. So blood flowing in them regulates the dissipation of heat. The fourth example of heat windows is the presence of lightly fared or naked areas. Some mammals which live under intense solar radiation have very lightly fared or naked areas present on their bodies. These areas facilitate heat loss through radiation, evaporation or conductive means. These parts include the axilla called armpits in humans, then groin region, udder of the animals, scrotum of mammals and the ventral body surface. These areas are lightly fared in many such animals which live in hot environments and need to dissipate heat. Some of these regions, for example, udder and scrotum have additional temperature sensors. These temperature sensors can detect changes in air temperature with minimal interference from the core body temperature. We shall discuss the evaporative heat loss. Evaporating water from the surface takes away heat and causes cooling effect. Many other vertebrates, panting or sweating mechanisms are used for evaporative cooling. Students' third method to dissipate heat is the postural changes. Postural changes can increase the rate of heat loss as per solar radiation. Animals adjust their postures so that their heat windows are either opened or shut, that is, either they are exposed or they are protected. The result is that the thermal conductance changes from animal bodies to the environment because of postural changes.