Homeostasis In Mammals.

        Osmoregulation is the regulation of the amount of water in the blood, in mammals this involves the kidneys and more specify the nephrons. Osmoregulation is controlled by the hypothalamus (found in the brain, otherwise known as the purity gland) sensitive to the level of water in the blood, if this is to fall too low the hormone ADH (anti diuretic hormone) is released into the blood, once this hormone has reaches the kidney, it will cause the walls of the collecting duct and the distal convoluted tubule (found in the nephrons) to become more permeable to water. Because of this more water is reabsorbed into the blood and the level of water in the blood rises. This process works both ways. If the level of water is too high within the body ADH will not be released into the blood causing little re-absorption of water into the blood this causes a dilute urine to be produced, where as a concentrated urine will be produced if there are high levels of ADH in the blood.

        Thermoregulation is the method by which animals control their internal body temperature. Animals fall into two categories where this is concerned: ectotherms or endotherms. Ectotherms, use external sources of heat, e.g. the sun to raise or maintain there body temperature. Reptiles such as lizards and snakes can often be seen basking in the sun on rocks in order to achieve this control over their body temperature. This method of thermoregulation is not very reliable in some cases as there may be factors that limit the ability of ectothermic animals to regulate their body temperature. All mammals are Endotherms, they use metabolic heat to maintain body temperature. In cold conditions mammals use a variety of methods to conserve their body temperature. In cold conditions muscles attached to the hair follicles contract, this causes the hairs to rise up and stand on end; this creates an insulating layer of warm air. This process is somewhat ineffective in humans. Vasoconstriction, is another way in which mammals try to maintain body heat, this is where muscles in the walls of arterioles contract, this causes less blood to flow to the surface of the skin and extremities, maintaining body heat to the vital organs in the centre body mass. Shivering is another mechanism used by mammals to maintain try to maintain body heat, fast repetitive muscular contractions create friction and thus warmth. There will also be instinctive behavioural changes that mammals shall go through to keep warm, in the case of humans trying to climb a mountain in a heavy storm, our natural instinct would be to find or build a shelter to protect ourselves from the elements and to slow down the process of heat loss. In the case of mammals needing to reduce their heat levels (in hot conditions) vasodilatation occurs, this is the opposite of vasoconstriction, blood vessels become wider allowing more blood to flow through, closer to the surface of the skin, thus allowing heat to be lost through the skin due to radiation. Sweating is another method used; the evaporation of water from the skin has a cooling effect on the body. This effect is due to a physical principal. To convert water to a vapour a certain amount of heat is required this is called the heat of vaporization. This heat will increase the speed at which the water molecules move, causing them to escape into the air and cool us down in the process. These mechanisms are mainly controlled by the hypothalamus, which contains temperature receptors that are sensitive to the temperature of the blood. It is this part of the brain that controls mostly all of the homeostasis in mammals.