BIO%20203.09%20Lecture%203s

# BIO%20203.09%20Lecture%203s - BIO 203 Lecture 3 Body...

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1 BIO 203: Lecture 3 - Body Temperature Prof. William Collins Office: 534 Life Sciences Building Office Hours: Mondays, 9:00 - 10:00 PM (on-line) Tuesdays, 11:30 AM - 12:30 PM Thursdays, 4:00 - 5:00 PM Convection : occurs when air or water moves over the body surface. modified form of conduction (slower) equation essentially the same as for conduction 1. Free convection—not mechanically moved Hot air rises—convective currents 2. Forced convection— physically making medium move

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2 Free Convection T amb = 20 o C T B = 37 o C 35 o 32 o 27 o Boundary Layers form when there is little or no forced air movement - rate of heat transfer very slow may be beneficial or harmful! Because of boundary layers, body senses environmental temperature as 35 o , not 20 o . Forced Convection T amb = 20 o C T B = 37 o C Physical movement of air disrupts boundary layers - higher rate of heat transfer Without boundary layers, body senses environmental temperature of 20 o . e.g., wind chill
3 Evaporation Transformation of water from liquid to vapor (gas). Requires energy Cools down environment 1 g H 2 O 580 cal (heat of vaporization) Evaporative Cooling : when water moves from liquid phase to vapor phase, it absorbs energy from the body surface cooling sweating (humans) panting (dogs / cats) H 2 O (liquid) low heat content heat from body surface H 2 O (vapor) high heat content Radiation Longer wavelengths—less energy (energy = 1/ λ ) If in thermal equilibrium: emitted==absorbed (IN = OUT) incident radiation reflected radiation emitted radiation (heat loss) absorbed radiation (heat gain) body surface in out

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4 in out in out black surfaces absorb radiation white surfaces reflect radiation (in all directions) Radiation Body Temperature Basic biological need : Need to keep T B fairly constant (or within a very limited range) so that cells (enzymatic processes) can function efficiently!
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