These include increasing the circulation of the blood to the surface of the body to allow for the dissipation of heat through the skin and initiation of sweating to allow evaporation of water on the skin to cool its surface. Conversely, if the temperature falls below the set core temperature, the hypothalamus can initiate shivering to generate heat. The body uses more energy and generates more heat. In addition, thyroid hormone will stimulate more energy use and heat production by cells throughout the body.
An environment is said to be thermoneutral when the body does not expend or release energy to maintain its core temperature. If the temperature is higher, for example, when wearing clothes, the body compensates with cooling mechanisms. The body loses heat through the mechanisms of heat exchange.
When the environment is not thermoneutral, the body uses four mechanisms of heat exchange to maintain homeostasis: conduction, convection, radiation, and evaporation. Each of these mechanisms relies on the property of heat to flow from a higher concentration to a lower concentration; therefore, each of the mechanisms of heat exchange varies in rate according to the temperature and conditions of the environment.
Conduction is the transfer of heat by two objects that are in direct contact with one another. It occurs when the skin comes in contact with a cold or warm object. For example, when holding a glass of ice water, the heat from your skin will warm the glass and in turn melt the ice.
Alternatively, on a cold day, you might warm up by wrapping your cold hands around a hot mug of coffee. Convection is the transfer of heat to the air surrounding the skin. The warmed air rises away from the body and is replaced by cooler air that is subsequently heated. Convection can also occur in water. The convection currents created by the temperature changes continue to draw heat away from the body more quickly than the body can replace it, resulting in hypothermia.
Radiation is the transfer of heat via infrared waves. This occurs between any two objects when their temperatures differ. A radiator can warm a room via radiant heat. On a sunny day, the radiation from the sun warms the skin. The same principle works from the body to the environment.
About 60 percent of the heat lost by the body is lost through radiation. Evaporation is the transfer of heat by the evaporation of water. Because it takes a great deal of energy for a water molecule to change from a liquid to a gas, evaporating water in the form of sweat takes with it a great deal of energy from the skin. However, the rate at which evaporation occurs depends on relative humidity—more sweat evaporates in lower humidity environments.
Sweating is the primary means of cooling the body during exercise, whereas at rest, about 20 percent of the heat lost by the body occurs through evaporation. Humans have a temperature regulation feedback system that works by promoting either heat loss or heat gain.
This arrangement traps heat closer to the body core, restricts heat loss, and increases blood pressure. If heat loss is severe, the brain triggers an increase in random signals to skeletal muscles, causing them to contract and producing shivering.
The muscle contractions of shivering release heat while using ATP. Temperature is the variable during normal body temperature regulation, but not in this scenario. Show Answer Answer d is correct. The hypothalamus is the control center for both normal body temperature homeostasis and febrile response.
The skeletal muscle, sweat glands, and blood vessels are all effectors. Show Answer Option b is correct. This would increase the body temperature. Option a would decrease the body temperature. Show Answer Option d is correct. Muscles, sweat glands, and blood vessels are effectors; they do not serve as a control center. Show Answer Option a is correct. This will cool the body. Option b would warm the body. Show Answer Option c is correct. The hypothalamus is still the control center that responds to a stimulus from some type of receptor.
Thermoreceptors and chemoreceptors stimulate the control center in response to a change in the variable they monitor, in this case body temperature. Thermoreceptors are located throughout the body, so it is unlikely an operation would directly damage all the receptors. All other options could be a cause of post-operative fever. Practice Questions Based on the above description of calcium homeostasis, try to answer these questions: What is the variable? What is the receptor?
What is the control center? What is the effector? Show Answers Option d is correct: calcium is the variable. Proper calcium levels are important for many body functions. Option b is correct: the endocrine system is the receptor. The endocrine system regulates many things.
Option b is correct: the endocrine system is the control center. The endocrine system can both sense and modulate calcium levels. Too cold When we get too cold: Muscles contract rapidly - we shiver. These contractions need energy from respiration , and some of this is released as heat. Blood vessels leading to the skin capillaries become narrower - they constrict - letting less blood flow through the skin and conserving heat in the body. The skin The hairs on the skin also help to control body temperature.
Skin hairs lie flat when we are hot and stand upright when we are cold Negative feedback mechanisms control body temperature. They include the amount of: shivering rapid muscle contractions release heat sweating evaporation of water in sweat causes cooling blood flowing in the skin capillaries Negative feedback in temperature regulation Vasoconstriction and vasodilation The amount of blood flowing through the skin capillaries is altered by vasoconstriction and vasodilation.
Too cold Too hot Process Vasoconstriction Vasodilation Arterioles Get narrower Get wider Blood flow in skin capillaries Decreases Increases Heat loss from skin Decreases Increases These diagrams show the processes that take place when vasoconstriction and vasodilation occur.
Vasoconstriction — a response to being too cold Vasodilation — a response to being too hot. Get narrower.
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