Regulation of Body Temperature

Regulation of Body Temperature by Endothermic Organisms
-Endothermic organisms are organism that generate heat internally in body to maintain body temperature.

Body Temperature is Higher than Normal Range:
-Increase in body temperature is detected by thermoreceptor in Hypothlamus while increase in external environment temperature is detected by thermoreceptor in skin.
-Temperature regulatory centre in hypothalamus receives impulse from the thermoreceptor
-Temperature regulatory centre transmit impulse to these effectors:
>Erector muscles in skin relaxes, hair on sin becomes slanted. Thinner layer of air is trapped among hair on skin. More heat is lost through surface of skin to produce cooling effect.
>Vasodilation of blood vessels in skin region occurs to increase rate of blood flow. Since blood transport heat, more heat is transported to skin region, more heat is lost through skin.
>Sweat glands in skin secretes sweat to surface of skin. Vapourisation of sweat releases latent heat of vaporisation, cooling effect occurs.
-All these processes increases heat lost from the body, body temperature decreases back to normal range.

Body Temperature Lower than normal range:
-Decrease in body temperature is detected by thermoreptor in Hypothalamus and decrease in external environment temperature is detected by thermoreceptor in skin.
-Temperature regulatory centre in hypothalamus receives impulses from the thermoreceptor.
-Temperature regulatory centre transmit impulse to these effectors:
>Erector muscle in skin contracts, hair on skin becomes erect. Thicker layer of air is trapped among hair on skin. The layer of air acts as insulating layer to reduce heat lost through skin.
>Vasoconstriction of blood vessles in skin occurs to reduce rate of blood flow to skin region. Less heat is transported to skin region, less heat is lost through skin.
>Medulla oblongata stimulates alternate contraction and relaxation of skeletal muscles, shievering occurs. Contraction of muscles releases heat that can be used to maintain body temperature.
>Adrenal gland secretes adrenaline to stimulates hydrolysis of glycogen in liver to glucose. Glucose produced is released into blood circulation to be used in energy/heat production.
>Thyroid gland secretes thyroxine to increase body metabolic rate. More heat is produced through metabolism to maintain body temperature.
- All of these processes decreases heat lost from body, body temperature increases back to normal range.


Regulation of Body Temperature by Ectothermic Organisms
-Ectotherms or poikiloterms include insects, reptiles, fish and amphibians.
-Ectotherms are animals that regulate temperature by receiving heat exogenously from sunlight.
-Their body temperature follow that of the external temperature (environment)
-Ectotherms control body temperatures by behavioural changes and not by physiological methods.
-Eg of behaviour changes of ectotherms to regulate body temperature:
i) Orientate body towards/away from sun rays to absorb/reduce absorption of heat-when body temperature is low/high.
ii) Move to warmer surface to absorb heat.
iii) Have body colouration to absorb or release heat- dark colours to absorb heat and pale colours reduce heat absorption.
iv)Move into water or burrow to absorb heat.
v)Remain dormant(inactive) or diapauses throughout winter.
vi)Painting or opened mouth to release heat by evaporation.