External temperature change Skin is the barrier between our body and the external environment and can be 2 or 3 degrees below core body temp Core body temp is maintained at about 37 degrees C Changes in the external temp causes changes in the temp of exposed skin. These changes are detected by two kinds of temp receptors - one detects cooling - one detects warming
External temperature change If there is a reduction in skin temp, the cold receptors register the change by increasing the rate of discharge of electrical information along the affector neurons
External temperature change If there is an increase in skin temperature, the heat receptors increase their rate of discharge along the affector neurons
External temperature change The number of different kinds of temperature receptors vary in different parts of the skin Affector or sensory neurons transmit impulses from skin temperature receptors to the Hypothalamus in the brain
Hypothalamus The temperature control centre of the body
Hypothalamus The hypothalamus plays a most significant role in the maintenance of core body temperature. It receives information about temperature change via sensory nerves from various parts of the body as well as detecting temperature change itself. The messages sent out by the hypothalamus in response depend on whether the information is that the temperature is higher or lower than 37°C
Internal temperature change Changes in core body temp are detected by a number of temp receptors within the body The most important of these are large numbers of temperature-sensitive receptors in the hypothalamus of the brain. The majority of these, ¾ of the total, are sensitive to heat, the remaining sensitive to cold.
Internal temperature change Other deep body temp receptors are near the spinal cord, around large veins and in parts of the digestive system. These transmit impulses via affector neurons to the hypothalamus.
HEAT TRANSFER PRINCIPLES CONDUCTION is the transfer of energy through matter from particle to particle. CONVECTION is the transfer of heat by the actual movement of the warmed matter. RADIATION Electromagnetic waves that directly transport ENERGY through space.
CONDUCTION Conduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance. For example, a spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction is most effective in solids-but it can happen in fluids. Fun fact: Have you ever noticed that metals tend to feel cold? Believe it or not, they are not colder! They only feel colder because they conduct heat away from your hand. You perceive the heat that is leaving your hand as cold.
CONVECTION Convectionis the transfer of heat by the actual movement of the warmed matter. Heat leaves the coffee cup as the currents of steam and air rise. Convection is the transfer of heat energy in a gas or liquid by movement of currents. (It can also happen is some solids, like sand.) The heat moves with the fluid. Consider this: convection is responsible for making macaroni rise and fall in a pot of heated water. The warmer portions of the water are less dense and therefore, they rise. Meanwhile, the cooler portions of the water fall because they are denser.
RADIATION Radiation: Electromagnetic waves that directly transport ENERGY through space. Sunlight is a form of radiation that is radiated through space to our planet without the aid of fluids or solids. The energy travels through nothingness! Just think of it! The sun transfers heat through 93 million miles of space. Because there are no solids (like a huge spoon) touching the sun and our planet, conduction is not responsible for bringing heat to Earth. Since there are no fluids (like air and water) in space, convection is not responsible for transferring the heat. Thus, radiation brings heat to our planet.
Evaporation Makes use of the principles of conduction, convection and radiation. The evaporation of water requires heat which is provided by the body Even if a person is not sweating, water still evaporates from the skin
Losing Heat Heat can be lost by the body through radiation, conduction, convection and evaporation
Gaining heat and reducing heat loss The hypothalamus initiates two kinds of responses to balance any loss of heat. Some responses generate heat, others reduce the rate at which heat is lost from the body
Heat production by Shivering Alternate contraction and relaxation of small muscle groups – involuntary Activated by the hypothalamus When muscles shiver almost all the energy is converted into heat energy Drains energy reserves so cannot be sustained for long
Heat production by metabolism Through a process of hormone production by the hypothalamus to the pituitary to the thyroid, thyroxine output is increased Thyroxine is a hormone that increases the metabolic rate of all cells of the body, resulting in an increase in heat production.
Heat production by metabolism Motor nerves from the hypothalamus also cause the medulla of the adrenal glands to secrete adrenaline and noradrenaline. These hormones increase basal metabolic rate, particularly in skeletal muscles and brown fat
Reducing heat loss through constriction of blood flow in skin Constriction of arterioles to reduce heat loss Refer back to vasodilation and vasoconstriction
Reducing heat loss through piloerection Hair standing on end Trapping a layer of air as a insulation layer between the skin and the external environment
Behavioural activities for temperature regulation List as many as you can for humans – heat loss, heat gain In hot weather, kangaroos and wallabies often lick their front legs. What benefit might this behaviour produce? Consider how a cat or dog sleeps in hot and cold weather. How are they limiting or increasing heat loss?
Big or small: which stays warm more easily? Consider both heat production and heat loss Heat production in relation to the units of skin surface
Costs of Homeostasis surface area to volume relationship heat is lost through surfaces as body size increases volume increases as a power of 3 surface area increases as a power of 2
Costs of Homeostasis lower SA / V (big mammals) = more precise temperature regulation less heat loss relative to thermal inertia of organism