WHAT  IS  MEAN  BODY  TEMPERATURE?
This presentation is the property of its rightful owner.
Sponsored Links
1 / 12

WHAT IS MEAN BODY TEMPERATURE? • Very different for different animals WHY? PowerPoint PPT Presentation


  • 52 Views
  • Uploaded on
  • Presentation posted in: General

WHAT IS MEAN BODY TEMPERATURE? • Very different for different animals WHY? Regional differences - core body temperature Hottest region - lumen of stomach + upper part small intestine - distinctly hotter than aortic blood

Download Presentation

WHAT IS MEAN BODY TEMPERATURE? • Very different for different animals WHY?

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


What is mean body temperature very different for different animals why

WHAT IS MEAN BODY TEMPERATURE?

• Very different for different animals

WHY?

Regional differences - core body temperature

Hottest region - lumen of stomach +

upper part small intestine - distinctly hotter than

aortic blood

(Grayson, 1983) - not due - digestive or

absorptive functions - nor to metabolism


What is mean body temperature very different for different animals why

Estimates of body temperature (steady-state conditions)

Tb = (a1 x Tcore) + (a2 x Tskin)

a factors = empirically determined contributions

of core & shell to mean body temperature

Some estimates : 9 : 1 and 6 : 4

Varies with thermal environment and investigator

•Tb = 0.67 Tre + 0.33 Tskin

Which thermal sensors are important?


What is mean body temperature very different for different animals why

How do you determine mean surface

temperature?

Humans:

Tskin = 0.07Tfeet + 0.32Tlegs + 0.18Tchest + 0.17Tback +

0.14Tarms + 0.05Thand + 0.07Thead

Periphery - skin, mucous surfaces (mouth, nose)

Core - spinal cord, hypothalamus, medulla oblongata, + organs

Difficult - determine by experiment - which are important sites


What is mean body temperature very different for different animals why

Chicken - exposed cold Ta -

shivers before change in deep body temperature

Suggests - heat production - controlled by thermal receptors in skin.

Kuhnen and Jessen - 1988 - goat

Change - skin temperature - alone -

alters MR


What is mean body temperature very different for different animals why

  • Populations of Temperature Sensitive Structures

  • (skin, spinal cord, hypothalamus)

  • Warm sensors - activity increases with local temperature increase

  • No discharge at skin temperature below 30 C

  • Receptors discharge with increase temperature

  • from 30 >> 35 C

  • •But little sustained activity

  • Further increase - skin temperature >> increased sustained

  • discharge that changes with temperature

  • Peak activity - 45-47 C

  • Activity ceases at higher temperature


What is mean body temperature very different for different animals why

  • Cold Sensors - activity decreases over same temperature range

  • Most active at 15 - 35 C & peak at 20 - 30 C

  • ===========================================================

  • PARADOXICAL RESPONSE

  • Most cold receptors >> no discharge above 35 C

  • But may get discharge near noxious level (43 - 47 C)

  • (ex. sudden chill - stepping into hot shower)

  • Also paradoxical warm receptor response - BUT not as common


What is mean body temperature very different for different animals why

Proportions - cold & warm sensors - vary with site

In general - more warm sensors - hypothalamus

more cold sensors - cutaneous regions

Exceptions - scrotal region - high concentration warm sensors

Sheep & rats - local heating scrotum >> powerful heat loss effector activity

If sustained >>> decrease in body temperature

Heating scrotum - ram - above 36 C >> panting & decrease

core body temperature (~ 2 C)

Similiar effects - heating mammary skin - ewe


What is mean body temperature very different for different animals why

General facts about skin temperature

Not homogenous - large difference in skin temperature in

different parts of the body

May account for regional differences by averaging surface area

•BUT - density of skin thermoreceptors are different in

different areas

Larger weight to face and less to extremities

•Face - approx. 20% of total skin signal


What is mean body temperature very different for different animals why

Skin temperature - represents interaction between

convective heat exchange to surface by

blood + removal of heat (geometry,

external insulation, ambient temperature)

Virtually all skin areas - including trunk -

constrict at cold Ta

(Exception = human forehead -

no vasoconstriction atcold Ta)


What is mean body temperature very different for different animals why

CENTRAL RECEPTORS

Under normal conditions - trunk sites do not

vary more than 0.5°C

Arterial temperature (e.g., carotid) - contain core temperature sensitive sensors

Hypothalamus - contains many neurons and thermoregulatory circuits

Preoptic Anterior Hypothalamus (POAH) still a

black box


What is mean body temperature very different for different animals why

During heat stress and exercise -

may maintain brain temperature below trunk

In panting carnivores - blood supply passes

through carotid rete

A net-like structure - base of brain

Numerous small arteries embedded in cavernous

sinus

Rete = heat exchanger


What is mean body temperature very different for different animals why

•Cooled venous blood - evaporating surfaces

(e.g., nasal mucosa)

•arterial blood entering brain

•running antelope - brain temperature ~3°C below

carotid temperature

•Also goat and sheep

•maintenance of lower brain temperature also found in

species without carotid rete (rabbit, squirrel,

monkey, man)

•Nonpanting animals - cool venous blood - sweating face

Site of exchange with arterial blood - unknown


  • Login