BSCI 1511 Lecture Notes - Lecture 17: Brown Adipose Tissue, Hypothalamus, Thermogenesis
26 Feb 2017
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Lecture 17: Thermoregulation
I. Balancing heat loss and gain: Insulation
a. Insulation = reduces overall heat exchange
i. Blubber, hair, feathers
b. Can often be adjusted to thermoregulate –can be rapid or seasonal
i. Momentary: raising hairs or feathers
ii. Seasonal (acclimatization): changes in the composition of the insulating
layer or layers
II. Balancing heat loss and gain: Circulatory adaptations
a. Circulatory adaptations = adaptations that regulate the extent of blood flow
near the body surface or that trap heat w/in the body core
i. Vasodilation (blood vessels expand) in skin increases transfer of body
heat to environment through conduction, convection, and radiation
1. Increased heat loss
ii. Vasoconstriction (blood vessels contract) in skin decreases transfer of
body heat to the environment through conduction, convection, and
radiation
1. Heat conservation
b. Countercurrent exchange = transfer of heat (or solutes) between fluids that are
flowing in opposite directions
i. Allows for heat exchange between arteries and veins that are traveling in
opposite directions
III. Balancing heat loss and gain: Evaporative cooling
a. Evaporative cooling = removal of heat from the surface of a liquid that is losing
some of its molecules as gas
i. E.g. sweat, dog sticking out tongue
IV. Balancing heat loss and gain: Behavioral responses
a. When cold:
i. Seek a warm place, huddle together, wear clothes
b. When hot:
i. Seek a cold place, seek space, bathe, shed clothes
V. Balancing heat loss and gain: Adjusting metabolic heat production
a. Thermogenesis = the generation of heat
i. Increased by muscle activity such as moving or shivering
ii. Can also occur by the burning of brown fat, which is rich in mitochondria
VI. Physiological thermostats
a. In mammals, thermoregulation is controlled by the hypothalamus
b. Warm sensors signal the hypothalamic thermostat when the temp of the blood
increases, activating cooling mechanisms
i. Blood vessels in skin dilate & we sweat
c. Cold sensors activate heating mechanism
i. shivering, blood vessels in skin constrict
VII. Fever and Torpor
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