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Chapter 9

Chapter 9 Textbook Notes - Temperature Regulation, Thirst and Hunger

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University of Toronto Mississauga
Ayesha Khan

Notes From Reading CHAPTER 9 TEMPERATURE REGULATION THIRST AND HUNGER PGS 254283 LO1 Explain the terms homeostasis set point and motivation Homeostasis HomeostasisA physiological state of equilibrium or balance To achieve homeostasis regulatory systems defend set points for variables such as temperature fluid levels and weight o Set PointA value that is defended by regulatory systems such as core temperature or a particular body weightThe process of motivation both activates and directs behaviour o MotivationThe process of activating and directing behaviour When homeostasis is compromised nervous system activates behaviour by producing tension in the form of drive states ex Thirst hunger o Drive states arise in response to physiological needs and go away when needs are metOnce organism is activated by a drive state it will initiate behaviour to solve problem Regulation of Body Temperature Involves a precisely defined set point mechanisms for detecting deviations away from set point internal and behavioural elements designed to regain set pointExtreme temperatures limit life through their impact on the chemical properties of living cellsThe amount of heat loss in a function of the body surface area and body volume determines the amount of heat generated by metabolic activityLO2 Describe the mechanisms and behaviors that ectotherms and endotherms use to maintain core temperatureAdaptations to Temperature EndothermAn animal that can use internal methods such as perspiration or shivering to maintain body temperatureEctothermAn animal that relies on external methods such as moving into the sun or shade for maintain body temperature Maintenance of body temperature is influenced by an animals surfacetovolume ration o The larger the overall volume the more heat is produced by metabolic activityBehavioral Responses to Heat and ColdEctotherms are more dependent on these behavioural devices because they do not share the endotherms ability to sue internal mechanisms for temperature regulationOne simple behavioural strategy for regulating temperature is to move to the right type of environment Body position can be adjusted in response to changes in temp o Too hotstretch out body to increase SA and lose more heat o Too coldcurl up to reduce SAAnimals can change weight colour and composition of their fur in response to seasonal changes Endothermic Responses to Heat and ColdNotes From Reading CHAPTER 9 TEMPERATURE REGULATION THIRST AND HUNGER PGS 254283Endotherms demonstrate automatic internal responses to deviations from temperature set pointo Shivering results from muscle twitches o Blood vessels constrict keeping most of the blood away from surface of skin where heat loss is greatest Raynauds disease when blood vessel constriction too extremedisease produces sudden spasms of arteriesIf cold persists thyroid gland increases release of thyroid hormoneHigh levels of thishormone is associated with greater overall metabolic activity to warm the bodyIn infants and small animals the sympathetic nervous system responds to cold by stimulating greater metabolic activity in brown fat cells located in torsobrown from highof mitochondriaWarm temperatureso Perspiration cools skin through evaporation o Blood vessels near the surface of the skin dilate in hot environments allowing more heat loss to external environment Deviations in Human Core Temperature Core temperature refers to the temperature maintained for vital organs within the head an torso Disturbance in ability to maintain normal core temperature can lead to hot flashedo Hot flashes characterized by sweating flushing heart palpitations o May be caused by changes in estrogen associated with menopauseFevers due to illness result when chemicals byproducts of bacteria or viruses known as pyrogens enter the brain causing the brain to increase core temperature set point o FeverA carefully controlled increase in the bodys thermal set point that is often helpful in ridding the body of diseasecausing organisms o PyrogensA chemical produced by bacteria or viruses that contributes to the production of a fever Benefits of fevero Raising set point kills many invading organisms which assists the immune system in ridding the body of disease o Pathogens reduced by fever ex The viruses responsible for many upper respiratory diseases and the bacteria responsible for gonorrhea and syphilis o Since there are some benefits to fever doctors suggest only using medication to reduce fever if other health risk factors are present or if discomfort is excessive Hyperthermia heat strokeA lifethreatening condition in which core body temperature increases beyond normal limits in an uncontrolled manner o When bodys normal compensations cant keep core temperature within normal limitso Symptoms if temp is over 40 Cperson can be confrontational faint and confusedsweating stops thus confounding problem of overheatingo Causes strenuous activity or wearing heavy clothing in hot environments
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