Lecture notes chapter 40

The implicacon of brown adipose tissue for humans

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Unformatted text preview: nd more heat is produced l This uncoupling allows brown fat cells to generate at least 10X more heat than is normally generated via cellular respiraCon What hormone regulates non ­shivering thermogenesis? thyroid hormone Is brown fat present in adult humans? yes, especially babies Up unCl recently, scienCsts did not believe that adults had significant amounts of brown fat Positron emission tomography scans helped scienCsts idenCfy brown fat in adults Neck and collarbone Near the spine Aorta and its main branches Near the adrenals Positron emission tomography (PET) images from the neck and thoracic region in one lean individual. ScienCsts think these deposits of brown fat funcCon to maintain core body temperature by generaCng and distribuCng heat From: Ravussin E and Galgani J. The ImplicaCon of Brown Adipose Tissue for Humans. Annual Review of NutriCon 2011; 31: 33 ­47. Physiological Thermostats sensors for regulating body temperature in humans are found in hypothalamus Sweat Gland: secretes sweat Evaporated Cooling Hypothalamus: Thermostat acCvates cooling mechanisms Heat lost from skin surface Blood vessels: dilate and fill with warm blood Decrease in body temperature: Thermostat shuts off cooling mechanisms Increase in body temperature: Thermostat shuts off warming mechanisms Divert blood from skin to deeper Cssues which reduces heat loss Skeletal muscles rapidly contract, causing shivering which generates heat Increase in body temperature Assume ambient temp is less than body temp Decrease in body temperature Blood vessels: constrict Hypothalamus: Thermostat acCvates warming mechanisms Bioenerge2cs: overall flow and transformaCon of energy in an animal * production and use of atp generates which is given off to the surroundings Remember: H2O ATP Pi + ADP + energy Metabolic Rate: The sum of all energy ­requiring biochemical reacCons over a given Cme interval Measured in joules, calories (cal) or kilocalories (kcal) Methods of measuring metabolic rate: Measure an animals rate of heat loss – calorimeter Measure amount of oxygen consumed or carbon dioxide produced Researcher collecCng respiratory data from a pronghorn running at 40 km/hr Animals must maintain a minimal metabolic rate for basic func2oning: ---------Cell maintenance Breathing Heart beat Measured differently for endotherms and ectotherms Basal Metabolic Rate: Applies to endotherms – must measure individuals: At rest FasCng Non stressed Comfortable temperature range Men: 1600~1800 kcal/day Women: 1300~1500 kcal/day Standard Metabolic Rate (SMR): Applies to ectotherms  ­ must measure individuals: At rest FasCng Non stressed ParCcular temperature Alligator: 60 kcal/day at 20C- much lower energy requirements for ectothermy Factors that Influence Metabolic Rate: age, sex, size, acCvity, temperature, and nutriCon RelaConship of BMR to body size Size increases 100 fold from shrew to elephant Direct relaConship between size of animal and it overall chemical energy requirements RelaConship of BMR per kilogram of body mass to body size * energy requirements to mainain each gram of body weight is inversely related to body weight Each gram of a mouse requires 20X as many calories as each gram of an elephant Energy Budgets for Four Animals Which animals do not grow as adults? penguins, deer mouse Which animal uses the greatest frac2on of its energy budget for thermoregula2on? deer mouse Which animal uses the smallest frac2on of its energy budget for thermoregula2on? eastern indigo snake Which animal uses the greatest frac2on of its energy budget to keep ac2ve? penguin...
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This document was uploaded on 02/10/2014.

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