Detecting Temperature ChangeDetecting Temperature Change

External temperature External temperature changechange

Skin is the barrier between our body and the external Skin is the barrier between our body and the external environment and can be 2 or 3 degrees below core environment and can be 2 or 3 degrees below core body tempbody temp

Core body temp is maintained at about 37 degrees CCore body temp is maintained at about 37 degrees C

Changes in the external temp causes changes in the Changes in the external temp causes changes in the temp of exposed skin. These changes are detected by temp of exposed skin. These changes are detected by two kinds of temp receptorstwo kinds of temp receptors- - one detects coolingone detects cooling- - one detects warmingone detects warming

External temperature External temperature changechange

If there is a If there is a reductionreduction in skin temp, the in skin temp, the cold receptors register the change by cold receptors register the change by increasing the rate of discharge of increasing the rate of discharge of electrical information along the affector electrical information along the affector neuronsneurons

External temperature External temperature changechange

If there is an If there is an increaseincrease in skin in skin temperature, the heat receptors increase temperature, the heat receptors increase their rate of discharge along the affector their rate of discharge along the affector neuronsneurons

External temperature External temperature changechange

The number of different kinds of The number of different kinds of temperature receptors vary in different temperature receptors vary in different parts of the skinparts 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

Mechanism of Thermoregulation

HypothalamusHypothalamus

The hypothalamus plays a most significant role The hypothalamus plays a most significant role in the maintenance of core body temperature. in the maintenance of core body temperature. It receives information about temperature It receives information about temperature change via sensory nerves from various parts of change via sensory nerves from various parts of the body as well as detecting temperature the body as well as detecting temperature change itself. change itself. The messages sent out by the hypothalamus in The messages sent out by the hypothalamus in response depend on whether the information is response depend on whether the information is that the temperature is higher or lower than that the temperature is higher or lower than 3737°C°C

Draw a negative feedback loop for Draw a negative feedback loop for temperature changetemperature change

Internal temperature changeInternal temperature change

Changes in core body temp are Changes in core body temp are detected by a number of temp detected by a number of temp receptors within the bodyreceptors 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 changeInternal temperature change

Other deep body temp receptors are Other deep body temp receptors are near the spinal cord, around large near the spinal cord, around large veins and in parts of the digestive veins and in parts of the digestive system. system.

These transmit impulses via affector These transmit impulses via affector neurons to the hypothalamus.neurons to the hypothalamus.

Maintaining Core TemperatureMaintaining Core Temperature

Ways of Ways of gaininggaining heatheat

Ways of Ways of losinglosing heatheat

Basic metabolic Basic metabolic processesprocesses

Evaporation of sweatEvaporation of sweat

ShiveringShivering PantingPanting

Exercise or other Exercise or other muscular activitymuscular activity

ConvectionConvection

Radiation and Radiation and conduction to the conduction to the bodybody

Radiation and Radiation and conduction from the conduction from the bodybody

HEAT TRANSFER PRINCIPLESHEAT TRANSFER PRINCIPLES

CONDUCTIONCONDUCTION is the transfer of energy is the transfer of energy through matter from particle to particle. through matter from particle to particle.

CONVECTIONCONVECTION is the transfer of heat by the is the transfer of heat by the actual movement of the warmed matter. actual movement of the warmed matter.

RADIATIONRADIATION Electromagnetic waves that Electromagnetic waves that directly transport ENERGY through space. 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

Convection is 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.

EvaporationEvaporation

Makes use of the principles of conduction, Makes use of the principles of conduction, convection and radiation.convection and radiation.

The evaporation of water requires heat The evaporation of water requires heat which is provided by the bodywhich is provided by the body

Even if a person is not sweating, water still Even if a person is not sweating, water still evaporates from the skinevaporates from the skin

Losing HeatLosing Heat

Heat can be lost by the body through Heat can be lost by the body through radiation, conduction, convection and radiation, conduction, convection and evaporationevaporation

Gaining heat and Gaining heat and reducing heat lossreducing heat loss

The hypothalamus initiates two kinds of The hypothalamus initiates two kinds of responses to balance any loss of heat. responses to balance any loss of heat.

Some responses generate heat, others reduce the Some responses generate heat, others reduce the rate at which heat is lost from the bodyrate at which heat is lost from the body

Heat production by Heat production by ShiveringShivering

Alternate contraction and relaxation of small muscle Alternate contraction and relaxation of small muscle groups – involuntarygroups – involuntary

Activated by the hypothalamus Activated by the hypothalamus

When muscles shiver almost all the energy is When muscles shiver almost all the energy is converted into heat energyconverted into heat energy

Drains energy reserves so cannot be sustained for Drains energy reserves so cannot be sustained for longlong

Heat production by Heat production by metabolismmetabolism

Through a process of hormone production by the Through a process of hormone production by the hypothalamus to the pituitary to the thyroid, hypothalamus to the pituitary to the thyroid, thyroxine output is increasedthyroxine output is increased

Thyroxine is a hormone that increases the Thyroxine is a hormone that increases the metabolic rate of all cells of the body, resulting metabolic rate of all cells of the body, resulting in an increase in heat production.in an increase in heat production.

Heat production by Heat production by metabolismmetabolism

Motor nerves from the hypothalamus also Motor nerves from the hypothalamus also cause the medulla of the adrenal glands to cause the medulla of the adrenal glands to secrete adrenaline and noradrenaline.secrete adrenaline and noradrenaline.

These hormones increase basal metabolic rate, These hormones increase basal metabolic rate, particularly in skeletal muscles and brown fatparticularly in skeletal muscles and brown fat

Reducing heat loss through Reducing heat loss through constriction of blood flowconstriction of blood flow in skin in skin

Constriction of arterioles to reduce heat Constriction of arterioles to reduce heat lossloss

Refer back to vasodilation and Refer back to vasodilation and vasoconstrictionvasoconstriction

Reducing heat loss through Reducing heat loss through piloerectionpiloerection

Hair standing on endHair standing on end

Trapping a layer of air as a insulation layer Trapping a layer of air as a insulation layer between the skin and the external between the skin and the external environmentenvironment

Behavioural activities for Behavioural activities for temperature regulationtemperature regulation

List as many as you can for humans – heat loss, List as many as you can for humans – heat loss, heat gainheat 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

as body size increases volume increases as a power of 3

surface area increases as a power of 2

Costs of Homeostasis

surface area to volume relationship

heat is lost through surfaces

less heat loss relative to thermal inertia of organism

Costs of Homeostasis

lower SA / V (big mammals) = more precise temperature regulation