ANSC 300 - Ch. 15 - Thermoregulation

Heat

Total energy of all molecules in an animal, container, etc.

Measured in Joules

Temperature

Average kinetic energy of molecules in a substance

Measured in Fahrenheit, Celsius or Kelvin

T/F. A bathtub and a cup of coffee can have the same temperature, but not the same amount of heat.

True

Homeotherms

Includes mammals and birds

Temperature stays constant

Tend to also be labeled as endotherms

Warm-blooded

Endotherms

Rely on internal heat

Poikilotherms

Includes reptiles, fish, and amphibians

Temperature varies

Considered to be ectotherms

Cold blooded

Ectotherms

Rely on external heat

Average temps of domestic animals

Between 97.7-103.1 F

Factors of animal temps

Exercise

Time of day

Ambient temp (temperature in the surrounding environment)

Digestion

Hydration

Which animals have the highest and lowest range of temperatures?

Highest: Birds

Lowest: Horses

Where are the three places temperature can be taken on animals?

Core, rectum, and skin

Which place is temperature commonly taken from in animals?

Rectum

Core temp

Where the key organs are

Most stable, but the most difficult spot to get temperature from

Skin temp

Has a wide range of temperature

Not as reliable as core and rectal temp

Pattern of diurnal temp

Lowest in the morning

Slowly increases during the day

Peaks in the late afternoon/early evening

Decreases again during the night

Pattern of nocturnal temp

Opposite of diurnal

Heat as a byproduct

Heat is a byproduct of all metabolic processes and moves down a gradient

Created by both ATP production and use

Heat loss is important to maintain body temp

What direction does heat transfer go in?

From things that are hot to things that are cold

What organs produce most of the body heat at rest?

Kidneys, heart, lungs, brain, and liver

Why do skeletal muscle generate a lot of heat?

Exercise and shivering

Correlation between body size and heat production/loss

The smaller the animal, the higher the metabolic rate, and thus more heat loss

Brown fat

Metabolically active and creates body heat

Certain newborn animals and animals that hibernate have it

Where is brown fat located?

Mostly around scapula and kidneys

How is brown fat metabolically different from white fat?

It has more mitochondria

What do epinephrine and norepinephrine do for heat production?

Increase metabolism

Linked to sympathetic nervous system

What does thyroid hormone do for heat production?

Increases during cold periods

Which animal would have the highest heat production per unit of body weight?

Mouse

How heat produced in respiratory system is removed

Exhalation

How heat produced in circulatory system is removed

Vasoconstriction and dilation

How heat produced in the digestive system is removed

Excretion of feces and urine

How does warm blood make its way to the surface of the body to be lost in the environment?

Sympathetic system synapses with smooth muscle in blood vessels (veins in particular), which is where epinephrine and norepinephrine are released to induce vasodilation, increasing blood flow to the skin and facilitating heat loss

Arteriovenous anastomoses

Shunts blood to superficial veins

Used to cool of an animal quickly

Radiation

Involves heat emitted between body and environment

Can gain and lose heat

No touching between objects

Most common type of short-wave is sun radiation

Radiation from body surface is a type of long wave

Convection

Transfers heat via moving air or water

Can gain and lose heat

Natural convection

Warm blood comes to veins and loses heat into the environment

Forced convection

A method of heat transfer that involves the movement of air or water induced by external forces, such as fans or pumps, which enhances heat exchange

Conduction

Requires direct contact to exchange heat

Can gain and lose heat

Thermal conductivity - how easily heat is conducted

Things that are high in conductivity

Metals

Things that are low on conductivity

Air, gases

What is the first thing one should do to lose heat from the body?

Drink or hose down with cool water

Evaporation

Can only lose heat

Insensible water loss: airway and skin

Thermoregulate by sweating, panting, and wetting of body surface

Thermoneutral Zone

Area where temperature is in a homeostatic state within the body, meaning body temperature is not going through heat or cold stress

Lower critical temp

Cold stress

Hypothermia

Left hand border of TNZ

Metabolic rate increases at this time because they are creating ATP to generate heat

Feed intake increases

Upper critical temp

Heat stress

Hyperthermia

Right hand border of TNZ

Metabolic rate increases at this time because they need to pant and/or sweat to stay cool

Feed intake decreases

UCT and LCT of domestic animals

UCT tends to not go above the upper 80s

LCT has a little more variety in the 60s, 50s, and 40s

Skin as a thermosensor

Tends to have more cold sensors than hot

Fluctuates because of exposure to the environment

Body core as a thermosensor

Located in thoracic and abdominal cavities

Stays relatively constant

Hypothalamus as a thermosensor

Gets feedback from skin and body core to determine the appropriate thermoregulatory responses to maintain homeostasis.

What happens when body temps rise above UCT

Vasodilation blood vessels (localized response)

Sweating

Panting

Behavioral changes

At higher temperature, which method of heat loss is used the most?

Evaporation

Sweating

Evaporative method

Horses, cattle, and humans mainly rely on this to cool themselves off

Apocrine gland

Eccrine gland

• Sympathetic system

  • Fight or flight response

  • Epinephrine and norepinephrine

  • Increase in metabolic rate

Apocrine gland

Hoofed animals

Linked with hair follicles

Eccrine gland

Primates

Set within epidermis of skin

When might sweating not work as well?

When humidity is high, reducing evaporation efficiency.

What animals tend to not sweat as much?

Dogs & pigs

Panting

Vital for dogs to lose heat (can happen in ruminants, cats, and birds)

Increase of dead space ventilation (no gas exchange is occurring)

Dogs: Pattern of rapid breathing with one occasional deep breath to have gas exchange in the alveoli

What animals do not pant?

Horses and pigs

What happens when body temp drops below LCT

Vasoconstriction of blood vessels

Shivering (rapidly contracting skeletal muscles to create ATP)

BAT (brown adipose tissue)

Hormone secretion (Thyroid)

Behavioral changes

T/F. Thermal conductivity and insulation are inversely related

True

Pyrogen

Substance that causes fever

Can be exogenous and endogenous

How does the body react to adjusting its setpoint?

The body alters physiological responses such as shivering, vasodilation, or heat production in order to maintain homeostasis in response to changes in temperature setpoints.

What mediates the fever response?

Prostaglandin E

Hypothermia

>25 C or 77 F - usually fatal

Exception is hibernation

Hyperthermia

Heat stroke

43-44 C or 109-11 F - usually fatal