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Chapter 9

CHAPTER 9.docx

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Janelle Leboutillier

CHAPTER 9 Between 1980 and 2002- # of obese adults in US doubled & rates of obese children and teens tripled. Obesity rates in US range from a low 18.7% (Colorado) to a high 32% (Mississippi). Anne Becker researched the impact of American TV on disordered eating in the South Pacific islands of Fiji. - Dieting was unknown in these cultures. - They valued a robust well-muscled body for both sexes. - Fijian language has a term, going thin, to express concern about noticeable weight loss. - i.e. they worry when someone loses weight. - American TV- arrived in 1995- led to higher rates of dieting and eating disorders. o 75% of teen girls reported themselves as too big/fat. o 17% reported deliberately inducing vomiting to control weight.  This figure was 3% prior to 1995. Homeostasis Word coined by Walter Cannon (1932). - Ability to adjust physiological processes to maintain a steady internal balance or eqbm. Set point: a value that’s defended by regulatory systems (e.g. core temperature or particular body weight). Deprivations from ideal values are assessed by the nervous system and it then motivates behaviors to regain ideal state. - This is called motivation- activates and directs behaviors. Regulation of Body Temperature The higher an animal’s surface-to-volume ratio, the harder it must work to maintain core temperature. Amount of heat loss is a function of the body surface area and body volume determines the amount of heat generated by metabolic activity. e.g. rats have a harder time maintaining core temperature than humans since their surface-to-volume ratio is larger. s-t-v ratios: Rat 1:6.67 Humans 1:35.3 Elephants 1:150 2 solutions evolved to help animals maintain optimum T in a varying environment: 1. Mammals & birds – called endotherms (endon= Greek word for within) since they can maintain T though internal metabolic activity. CHAPTER 9 2. Amphibians, reptiles, fish- called ectotherms (ektos is Greek for outside) since they rely on external factors like sunlight/shade. *Common terms are warm blooded and cold-blooded but are misleading. In cold climates, surface area and heat loss are reduced in animals with compact, stocky bodies and short legs, ears and tails. To promote heat loss, animals in warm climates have greater surface area- slim bodies, long appendages. Ectotherms depend more on behavioral devices to maintain temperature. - e.g. move environments - e.g. body position- we curl when cold and stretch out when too warm. - Social animals huddle together when cold. - Animals can change weight, color, and composition of fur in response to seasonal changes in T. - Further protection is provided by dens, burrows, nests, & other shelters. Endotherms have automatic internal responses to deviations from a T set point: Humans defend a temperature set point of 37 C or 98.6 F. o Below set point: we shiver - Muscles twitch; blood vessels constrict to keep blood away from skin - Raynaud’s disease: when blood vessel constriction is too extreme; creased sudden spasms in arteries of fingers and toes in response to cold; affected digits lose feeling and appear white. - If cold persists in spite of shivering, the thyroid gland increases the release of thyroid hormone, which is associated with increased metabolic activity to warm the body. - Deficits in thyroid activity are diagnosed on the basis of the patient’s lower than normal body temperature. - In human infants or small animals, the sympathetic nervous system responds to cold by increasing metabolic activity in brown-fat cells. o Located in torso, close to vital organs. o Cells appear brown due to large numbers of mitochondria. Very warm temperatures: - Perspiration cools skin through evaporation - Humans have 2.5 million sweat glands and lose a liter (0.22 gallon) of sweat per day. - Animals like dogs don’t perspire a lot- they lick their fur and pant. - Blood vessels near skin dilate- causes red-face. Core t- t maintained for vital organs &torso - disturbances in core t leads to hot flashes (80% of women in months/years around menopause) hot flashes: seconds to mins - sweating, flushing, feelng warm, heart palpitations - dueto changes in estrogen CHAPTER 9 - freq and severity increase is alcohol used daily. High fever- 41C or 105.8F - causes brain damage pyrogens: a chemical product by bacteria/viruses that contributes to the production of a fever. - Cause brain to increase core t set point Pathogens reduced by fever: viruses responsible for many upper respiratory diseases, bacteria responsible for gonorrhea and syphilis. - Prior to AB, people w syphilis were infected with malaria to induce fever. - Reduce fever only is it has other health risk factors or discomfort is excessive. Hyperthermia: body’s normal compensations cannot keep core t at set point. - If rises above 40C/104F- person becomes confrontations, faint, confused. - Sweating stops - Life threatening - Strenuous activity, wearing hot/heavy clothes in hot humid place - People with existing infections more likely to get it during exercise 1995-2001- 16 footballers died e.g. Stringer had core t of 108F surface to volume wasn’t in his favor. Hypothermia- kills ocean swimmers and hikers. - T below 35C or 95F - Intense shivering, slurred speech, pain and discomfort - Below 31C/87.8F- pupils dilate, looks drunk, consciousness lost - Deliberately used to decrease brain damage after cardiac arrest, open heart surgery. - Use special mattress, IV fluids, and application of ice. - Counteracts typical – reactions to interruption of blood supply (e.g. increased activity of free radicals, excitatory NT and Ca. Brain Mechanisms for T regulation Sensitivity to T increases from lower to higher in hierarchy (SC, brain stem, hypothalamus). SC doesn’t respond till core T is 2-3C away from set point. - People with SC damage (prevents regulation by brainstem/hypothal) complain that they cannot manage T of arms/legs. Higher level- hypothalamus- acts if T deviates as little as 0.01C. Preoptic area (POA) of hypothalamus, anterior hypothalamus, septum- coordinate info from thermoreceptors with to structures that can trigger responses to increase core T – sweating/panting/dialation of vessels. CHAPTER 9 Postrior hypothalamus- initiates response to cooler core T- shivering/vessel contriction. Hypothalamus- receives input from skin and SC, also has its own thermoreceptors. POA has 3 neuron types: Warm sensitive, cold sensitive and temperature insensitive. Warm sensitive neurons inhibit cold sensitive in response to high body T. As body t drops, warm ones fire less and cold ones are activated. Temp-insensitive have constant firing Experiements showed that temperature sensors in hypothal can override input from skin sensors. Rats can press leaver to get a puff of cold air. Skin temp mirrors room temp Hypothal manipulated by bathing it with warm/cool water through surgically applied micropipette. If skin/hyp t raised, rat presses leaver more often. Cool hypo alone suppresses p
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