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Lecture 6

PSYB64 Lecture 6.docx

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University of Toronto Scarborough
Elizabeth Page- Gould

PSYB64 Lecture 6 “Temperature, Regulation, Thirst, and Hunger” 1. Homeostasis 2. Temperature 3. Thirst 4. Hunger 5. Obesity & Hunger Disorders HOMEOSTASIS  Homeostasis: Physiological equilibrium  Motivation: Activating and directing behavior  Regulation of Body Temperature Set point Mechanisms for detecting deviation Internal and behavioral elements to regain set point  Adaptations to Temperature Endotherms maintain constant body temp. Ectotherms body temp. same as environment = amphibians, reptiles and most fish Surface-to-Volume Ratios Affect Temperature Regulation  The higher an animal’s surface to volume ratio the harder it must work to maintain core temperature  Small animals have larger surface to volume ratios hence maintaining core temperature is harder for them than for larger animals? Who works harder to maintain this ratio, the rat of the human?  Behavioral Responses to Heat and Cold Ectotherms more dependent on behavioral devices Changes in position, weight, color and composition of fur  Endothermic Responses to Heat and Cold Automatic internal response to deviations in temperature Responses to lower temperatures Shiver Blood vessels constrict Thyroid hormone increase Responses to lower temperatures Perspiration, licking Blood vessels dilate  Deviations in Human Core Temperature Fever Heat stroke (hyperthermia) Hypothermia Emergency Hypothermia video clip  Brain Mechanisms for Temperature Regulation See Fig 9.7  Temperature Regulation in Infancy Relatively helpless in adapting to temperature HYPOTHALAMUS CONTROLS TEMPERATURE REGULATION THIRST: REGULATION OF THE BODY’S FLUID  Intracellular and Extracellular Fluids Extracellular fluid (33%) Intracellular fluid (67%)  Osmosis Causes Water to Move Water moves from an area with lower concentration of solutes to an area with higher concentration Hypotonic versus hypertonic  The Role of the Kidneys Excretes excess fluids and sodium THE BODY’S FLUIDS ARE HELD IN THREE COMPARTMENTS Osmosis Causes Water to Move SOURCES OF TYPICAL DAILY FLUID LOSS AND INTAKE IN HUMANS THIRST: REGULATION OF THE BODY’S FLUID  The Sensation of Thirst Occurs as a result of osmotic (drops in the intracellular fluid volume) and hypovolemic (drops in blood volume) thirst Can you think of examples of when these may occur?  Mechanisms of Osmotic Thirst Osmoreceptors located in the brain Organum vasculosum of the lamina terminalis (OVLT)  Mechanisms of Hypovolemic Thirst Baroreceptors measure blood pressure Receptors in the heart and kidneys Detecting Osmotic Thirst HYPOVOLEMIC THIRST (mechanisms of hypovolemic thirst) THIRST: REGULATION OF THE BODY’S FLUID  Hormones, Sodium, and Thirst Antidiuretic hormone (ADH) or vasopressin Low blood volume stimulates hunger for sodium  Initiation of Drinking Begins when angiotensin II acts on subfornical organ (SFO)  Cessation of Drinking Fluid receptors in mouth, throat, digestive system Hyponatremia Antidiuretic Hormone Begins a Sequence of Events Leading to Fluid Conservation  Thirst and Sports Drinks Prov
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