MEDICAL ANIMATION TRANSCRIPT: All structures in the body function together to maintain homeostasis, a process by which the body maintains its internal environment in response to the external environment. Examples of how the body maintains homeostasis include metabolism of drugs and toxins in the liver, regulation of water and solutes in the blood by the kidneys, regulation of blood glucose by the pancreas. Another homeostatic process, thermal regulation, is the maintenance of normal body temperature. If the body's skin or core temperature drops, thermoreceptors in the skin or internal organs send impulses to the hypothalamus, which acts as the body's thermostat. The hypothalamus responds through the sympathetic nervous system by constricting blood vessels in the skin. Vasoconstriction diverts blood away from the skin and extremities to the warmer interior of the body to prevent further loss of heat to the surroundings and prevent the body's core temperature from dropping further. Arrector pili muscles contract, causing piloerections in which hair follicles stand up in an attempt to trap warm air next to the skin. A continued drop in temperature prompts the hypothalamus to send impulses that elicit a shivering reflex in skeletal muscles, generating additional heat to increase body temperature. If the body's skin or core temperature increases, thermoreceptors in the skin or internal organs prompt the hypothalamus to halt sympathetic stimulation of blood vessels in the skin. The vessels dilate and allow warm blood to distribute heat through the skin. Arrector pili muscles relax and hair follicles lie flat against the skin. Sweat glands produce sweat, allowing heat loss through evaporation. The stimulus or decrease in body temperature causes the brain to act as a thermostat and dissipate heat throughout the body. Once normal temperature is reached, the thermostat shuts off. These examples of the body's response to counteract stimuli are called negative feedback loops, which allows the body to maintain homeostasis.