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University of Toronto Scarborough
Janelle Leboutillier

PSYB64: Introduction to Physiological Psychology Lecture 5: Temperature, Regulation, Thirst, & Hunger Overview 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 o Set point o Mechanisms for detecting deviation o Internal and behavioral elements to regain set point  Adaptations to Temperature o Endotherms  Maintain constant body temp. o Ectotherms  Body temp. same as environment = amphibians, reptiles and most fish Multiple Thermostats in the Nervous System 1. Hypothalamus: Set zone = 37 degrees 2. Brain stem: Set zone = 36-38 degrees 3. Spinal cord: Set zone = 35-39 degrees 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 or the human? RAT WORKS HARDER TO MAINTAIN TEMPERATURE Homeostasis  Behavioral Responses to Heat and Cold o Ectotherms more dependent on behavioral devices o Changes in position, weight, color and composition of fur  Endothermic Responses to Heat and Cold o 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 Adaptations of Appendages to Climate  Animals in warm climates disperse heat by having slim bodies and long appendages  Animals in cold climates conserve heat by having compact, stocky bodies and short legs, tails, and ears  These foxes are found in (left) warm, (center) temperate, and (right) Arctic climates. Homeostasis  Deviations in Human Core Temperature o Fever  Controlled increases in core temp set point during illness o Heat stroke (hyperthermia)  Occurs when core temperature increases due to failure of compensatory mechanisms o Hypothermia  Usually results from exposure to extremely cold environments  Emergency Hypothermia video clip   Can hypothermia be a good thing for people who have cardiac arrest?  Raynauds Disease o Blood vessels constrict, keeping most of the blood away from the surface of the skin where heat loss is greatest o With this disease the blood vessel constriction is too extreme causing sudden spasms in arteries often in the fingers and toes in response to cold  Brain Mechanisms for Temperature Regulation See Fig 9.7  Temperature Regulation in Infancy o Relatively helpless in adapting to temperature o Consider also rat pups in social environment The Hypothalamus Controls Temperature Regulation (Figure 9.7)  The preoptic area (POA) of the hypothalamus, along with adjacent areas of the anterior hypothalamus and septum, coordinates incoming information from thermo-receptors with structures responsible for appropriate responses to higher core temperatures such as panting, sweating, and the dilation of blood vessels  The posterior hypothalamus is responsible for initiating responses to cooler core temperatures such as shivering and blood vessel constriction.  Backup systems for temp control are located in the brainstem and spinal cord  POA responds to warm temps  Posterior hypothalamus responds to cool temps Thirst: Regulation of the Body’s Fluid  Intracellular and Extracellular Fluids o Extracellular fluid (33%) o Intracellular fluid (67%)  Osmosis Causes Water to Move o Water moves from an area with lower concentration of solutes to an area with higher concentration o Hypotonic (lower solute conc.) versus hypertonic (higher solute conc.)  The Role of the Kidneys o Excretes excess fluids and sodium The Body’s Fluids Are Held in Three Compartments (Figure 9.8)  About two thirds of the body’s fluid is stored as intracellular fluid  The remaining third is stored as extracellular fluid, divided between the interstitial fluid (anything in between) surrounding cells (26 percent) and the blood supply (7 percent)  The cerebrospinal fluid accounts for less than 1 percent of the body’s fluids. Osmosis Causes Water to Move (Figure 9.9)  Water will move from an area of higher concentration of solutes to an area of lower concentration of solutes  When salt is added into a tube separated from a container by a membrane, water will enter the tube to equalize the concentration of solutes on both sides of the membrane  When water is added to the tube, water will move into the container Sources of Typical Daily Fluid Loss and Intake in Humans (Table 9.1) TYPICAL DAILY LOSS TYPICAL DAILY INTAKE Source Approximate Daily Source Approximate Daily Quantity Quantity Urine 1.4 Liters Fluids from 1.2 liters beverages Perspiration, Fluids contained in evaporation, 0.9 Liters food 1.0 liters respiration Feces 0.2 liters Water 0.3 liters TOTAL LOSS 2.5 liters TOTAL INTAKE 2.5 Liters Thirst: Regulation of the Body’s Fluid  The Sensation of Thirst o Occurs as a result of osmotic (drops in the intracellular fluid volume) = exercising and hypovolemic (drops in blood volume) thirst = loss of a lot of blood  Can you think of examples of when these may occur?  Mechanisms of Osmotic Thirst o Osmoreceptors located in the brain o Organum vasculosum of the lamina terminalis (OVLT)  Mechanisms of Hypovolemic Thirst o Baroreceptors measure blood pressure o Receptors in the heart and kidneys Detecting Osmotic Thirst (Figure 9.10)  The organum vasculosum of the lamina terminalis (OVLT), located near the third ventricle, contains osmoreceptors that detect osmotic thirst  The subfornical organ (SFO) initiates drinking in response to detection of angiotensin II  Along with the nucleus of the solitary tract, the SFO communicates with the median preoptic nucleus of the hypothalamus  The median preoptic nucleus communicates with the zona incerta by way of the lateral hypothalamus  The zona incerta connects with a number of motor areas responsible for drinking behavior.  OVLT detects cellular dehydration  SFO, solitary tract, MPOA, zona incerta connects with motor areas responsible for drinking behaviour Hypovolemic Thirst (extra-cellular) Thirst: Regulation of the Body’s Fluid  Hormones, Sodium, and Thirst o Antidiuretic hormone (ADH) or vasopressin o Low blood volume stimulates hunger for sodium  Initiation of Drinking o Begins when angiotensin II acts on subfornical organ (SFO)  Cessation of Drinking o Fluid receptors in mouth, throat, digestive system o Hyponatremia Antidiuretic Hormone Begins a Sequence of Events Leading to Fluid Conservation (Figure 9.11) Thirst: Regulation of the Body’s Fluid  Thirst and Sports Drinks o Provides more sodium than other beverages, which helps athletes retain fluids and may prevent hyponatremia o Saltier tastes encourages athletes to drink more  What is HYPONATREMIA? o An electrolyte disturbance in which sodium concentra
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