ANSC 300 Thermoregulation

Heat vs. Temperature

• ***heat and temperature are NOT the same***

• Heat: total energy of all molecules, measured in joules (is transferred to an object; ex.- how the stove heats the pot)

• Temperature: avg. kinetic anergy of molecules in a substance measured in F, C, K (how hot or cold an object is)

HOMEOtherms

mammals/birds

• temp stays constant

• ENDOtherms: rely on internal heat

POIKILOtherms

reptiles

• temp varies

• ECTOtherms: rely on external heat

What is the Average Temperature of Most Domestic Animals?

97.7 - 103.1 F

• Core vs. Rectal/Skin Temperature

  • Rectal Temp: represents a true steady state of temperature because it reaches equilibrium more slowly

  • Core Temp: “deep body temp”; higher than the temperature of the limbs or even higher than the temperature observed rectally

• Factors:

  • exercise

  • time of day

  • ambient temperature

  • digestion

  • hydration

Diurnal Temperatures

• variations in temperature that are related to the time of day

  • animals that are ACTIVE during the DAY and SLEEP at NIGHT have body temperatures that are lower in the morning than in the afternoon.

  • the opposite is true for nocturnal animals

Heat

• is a byproduct of all metabolic processes, and moves down a gradient

• important for core body temp in endotherms

• created by both ATP production and use

• heat loss is important to maintain body temp!!

At Rest, the Majority of Body Heat is Produced in a Few Key Locations Such As _________

• Kidneys: 0.5% of body mass ; 7% of heat production

• Heart: 0.5% of body mass ; 9% of heat production

• Lungs: 1.0% of body mass ; 4% of heat production

• Brain: 2.0% of body mass ; 18% of heat production

• Liver: 2.5% of body mass ; 26% of heat production

  • SUM of HEAT PRODUCTION: 64 ——- SUM of BODY MASS: 6.5

• Skeleton & Muscles: 42.0% of body mass ; 26% of heat production

• Skin: 7.5% of body mass ; 2% of heat production

• Other: 44.0% of body mass ; 8% of heat production

  • SUM of HEAT PRODUCTION: 36 ——— SUM of BODY MAS: 93.5

***When will the Skeletal Muscles Generate more Heat?***

• shivering

• exercise

____________ and ____________ are Correlated.

Body Size & Heat Production/Loss

• metabolic rate is linked to heat production!

BROWN Fat

• is metabolically active and creates body heat

Who Has It?

• certain newborn animals

• animals that hibernate

• LOCATION: mostly around the scapula & kidneys

• metabolically different and more active than white fat; Why? — Because it has more mitochondria

What Hormones Aid in Heat Production?

• Epinephrine & Norepinephrine

  • increase metabolism

  • are the stimuli for increased metabolism of brown fat

• Thyroid

  • increases during cold periods

How do we Remove Heat Produced from the Body?

1. Respiratory System: helps remove excess heat from the body through breathing

2. Circulatory System: removes heat from the body through vasodilation, heat dissipation, sweating, and vasoconstriction

3. Digestive System: doesn’t DIRECTLY remove heat from the body, BUT it occurs with digested food, then it gets circulated, and then the hypothalamus dissipates the heat

Circulatory System

• is important for dissipating heat

• the sympathetic system regulates the vessel diameter

  • Heat Loss

  • Heat Conversion

_____ ______ is Brought to the Surface of the Body, to be Lost to the Environment.

warm blood

• sympathetic system

• Arteriovenous Anastomoses

  • direct connections between arteries and veins that shunt blood to superficial veins

  • shunting is important in regulating body temperature and occurs in areas like the skin of the hands and feet

Exchange of Heat Between the Body and the Environment Occurs in Many Ways Such As ____________.

1. Radiation: transfers heat through electromagnetic waves

2. Conduction: transfers heat through direct contact

3. Convection: transfers hat through the movement of fluids

4. Evaporation

***All heat exchange follows a heat gradient***

Radiation

• involves the heat that is emitted between the body and environment

• can gain and lose heat via radiation

• Daytime: Sun #1

• What Else is Outside?

  • farm buildings, coat color

Conduction

• requires direct contact to exchange heat

• can gain and lose heat via conduction

• Thermal Conductivity: how easily heat is conducted

  • Low: air, gases

  • High: metals

• Farm buildings

• Surgery?

Convection

• transfers heat via moving air or water

• can gain and lose heat via convection

• natural vs. forced convection

  • NATURAL: any fluid motion caused by natural means such as buoyancy

  • FORCED: fluid is forced for flow over a surface or in a tube by external means

• wind chill!

• fans

• transportation?

Evaporation

• involved the conversion of water to vapor

• can ONLY LOSE heat via evaporation

• Insensible Water Loss: airway and skin

  • not part of thermoregulation

• Thermoregulation:

  • sweating

  • panting

  • wetting of body surface

Thermoneutral Zone (TNZ)

shows where animals become stressed due to heat loss/gain

• where heat production and heat loss are canceling each other out (they’re equal)

  • ex.- homeostasis

• UCT (right side): heat stress, HYPERthermia, metabolic rate increases to dissipate excess heat

• LCT (left side): cold stress, HYPOthermia, metabolic rate increases to generate more hear

TABLE

• Beef Cattle & Dairy Cow= UCT(77,25) & LCT(32,0 , 60,15 , -22,-30)

• Sheep & Lamb= UCT(88,31) & LCT(72,22)

• Horse= UCT(86,30 , 68,20) & LCT (41,5 , 5,-15)

• Dog= UCT(86,30) & LCT(59,15)

***Animals are more comfortable at colder temperatures***

The ______ the animal, the _______ the Metabolic Rate Per Unit Weight.

smaller; higher

Thermosensors

monitor changes in body temperature

1. Skin

   • cold, hot

2. Body Core

3. Hypothalamus

Hypothalamus

is the *thermostat*

• Sensory Input

  • Warmth and Cold Sensors In: skin, internal organ, hypothalamus

• Motor Output

  • Heat Stress: behavior, increased skin blood flow, sweating, panting

  • Cold Stress: behavior, reduced skin blood flow, shivering, activation of brown adipose tissue, hormone secretion

There are More ____ _________ than Hot Receptors on the Skin

cold receptors

When Temperatures RISE, We are ABOVE the _______

UCT

• vasodilation blood vessels

  • more blood to skin

• sweating

• panting

• behavioral changes

  • ex.- reduce activity, drink more water, eat less

Vasodilation & Vasoconstriction is a _______ ________

localized response

• NOT systemic

At Higher Environmental Temperatures, __________ is Used More.

evaporation

Sweating

• is important for horses and cattle (and us too!)

  • Apocrine Gland: hoofed animals; is linked to a hair follicle

  • Eccrine Gland: primates; is NOT linked to a hair follicle

  • Sympathetic system

  • Dogs & Pigs: not important

***When Might Sweating Not Work As Well?***

• when it is super humid outside, our sweat slowly drips off our body and our body’s cooling system becomes hindered in a humid and hot environment → biggest risk for heat stress/hyperthermia.

Panting

• is vital for dogs to lose heat (also ruminants, cats, birds)

• Dead Space Ventilation: space where gas exchange doesn’t occur

• Horses & Pigs: not important

When Temperature DROP, We are BELOW the ______

LCT

• vasoconstriction blood vessels

  • less blood to the skin

• shivering

• BAT (brown adipose tissue)

• hormone secretion

• behavioral changes

Behavioral Adaptations to Cold

• huddling

• curling up

• piloerection of hair

• body adjustments

• plumage “fluff”

______ ________ and _________ are Inversely Related.

Thermal Conductivity & Insulation

• ***What Happens if an Animals Gets Wet?***

  • they will lose heat more rapidly (bad in winter, good in summer)

Fever

• elevates the normal setpoint of temperature → pyrogens are to blame!!

• defense mechanism against microorganisms

• Pyrogen: substance that causes fever

***How Does the Body React to Adjusting the Setpoint?***

• illustrated on graph

Pyrogen

can be exogenous and endogenous

• prolonged high fevers can cause damage

  • above 41 C, 106 F

• Prostaglandin E: mediates fever response

Hypothermia

• >25 C or 77 F; usually fatal

• Exception

Hyperthermia

• heat stroke

• 43-44 C or 109-111 F; usually fatal