Thermoregulation

1. Thermoregulation • “The maintenance of a particular temperature of the living body” –Mariam-Webster • Ideal temperature • Regulation • Hypothalamus • Hypothermia • Hyperthermia • Thermogenesis

2. The Merck Veterinary Manual

3. Regulation • External heat transfer mechanisms • Radiation-emission of infrared radiation • Conduction-transferring through physical contact • Convection-transfer by movement of liquid or gas between areas of different temperature • Evaporation-conversion of liquid to vapor • Regulated by neural feedback mechanisms that operate through the hypothalamus primarily • Hypothalamus contains control mechanisms & key temperature sensors

4. Hypothalamus • Group of neurons in anterior portion- preoptic area • As temperature rises neurons increase activity • As temperature drops neurons decrease activity • Nerve impulses of the preoptic area work with heat-loosing and heat-promoting centers of the hypothalamus

5. Hypothermia • Animals can have low temperatures after birth due to dystocia and being hypoxic • Feed warm colostrum • Can partially compromise the immune system • Newborn has a poorly developed ability to shiver • Low volume but high surface area for the heat to escape

6. Hypothermia • Responses initiated to save body heat and increase heat production • Vasoconstriction to decrease the flow of heat to the skin • Cessation of sweating • Shivering to increase heat production in the muscles • Secretion of norepinephrine, epinephrine and thyroxine to increase heat production by increasing the BMR • Raising of hairs to increase insulation • Production of thyroid hormones that initiate burning of food • Thyroid hormones regulate BMR

7. Hyperthermia • Fat layer-can be thin in newborns • Arterioles dilate to move heat out through the skin • Sweating • The mother keeps the fetus warm • Fetus and placenta have such a high metabolic rate that the fetus is ~.5⁰C warmer than the mother (Orville, 2014)

8. Thermogenesis • “The production of heat especially in the body (as by oxidation)” –Mariam-Webster • Brown Adipose Tissue • Born with most at birth • Usually 2-4% of birth weight (Symonds, 2013) • Thermogenic capacity is at peak at birth • Adult’s amount increases with exposed to cold & decreases with age and BMI • In lower neck/chest • In lumps like glands

9. Thermogenesis • Functions to distribute stored energy as heat • Large number of mitochondria-produce ATP • Produced through activation of uncoupling protein 1 (UCP1) • Can produce up to 300 watts/kg of heat • All other tissue can only produce up to 1 watt/kg • Pigs lack brown adipose tissue • Nonfunctional UCP1 gene • Dependent on shivering thermogenesis (Symonds 2013)

10. Thermogenesis • Non-Shivering Thermogenesis • Cold exposure causes sympathetic stimulation of brown adipocytes by norepinephrine binding to beta-adrenergnic receptors • In brown adipocytes, most fatty acids are directly oxidized and a large amount of heat is produced • In white fat, sympathetic stimulation causes hydrolysis of triglycerides • Release of glycerol and fatty acids • More for insulation than heat production

11. (Symonds, 2013)

12. Thermoregulation • PGC1α-master regulator of mitochondrial biogenesis in many species • Required to heat production of BAT • By decreasing thyroid hormones in the plasma by blocking the secretion or being in a warm environment leads to a loss of UCP1 and enhances the breakdown of white adipose tissue • Hypothyroidism as a newborn leads to impaired thermoregulation and sometimes death (Symonds, 2013)

13. 4 Stages of Adipose Tissue Development in Early Life Summary of the main developmental changes in adipose tissue during early life. (Symonds, 2013)