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Lecture5 - Temperature Regulation, Thirst, and Hunger

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Ayesha Khan

PSY290H5S – Introduction to Physiological Psychology Lecture 5 – July 29, 2013 Chapter 9 – Temperature Regulation, Thirst, and Hunger - Motivation o How can something like temperature of regulates affect the choices we make? Homeostasis - Homeostasis: Physiological equilibrium o The process that results in balance that the body has in place so that things don’t fall apart o An organisms ability to adjust its behaviour for an equilibrium to occur, is related to biological psychology - Motivation: Activating and directing behavior - Regulation of Body Temperature o Set point  tells your body if your temperature deviates from a set point, something needs to happy to bring the body back to the set point o Mechanisms for detecting deviation o Internal and behavioural elements to regain set point - Adaptations to Temperature o Endotherms  mammals, birds  Inside; have to reply on internal factors o Ectotherms  amphibians, reptiles, fish  Outside; have to rely on external factors Drive-Reduction Theory ** - There is a need for survival - Biological needs o Hunger, thirst, sleep, oxygen, elimination of bodily wastes o Body is assessing, “is this body in a state of balance?” If is not, ie not enough water, you think about drinking more water o This gives rise to a drive - Drive – internal state of tension or arousal o Any given moment in time, you had a meal, your body starts taking up the nutrients and either start to use them or store them o Leads to participate in goal erected behaviour - Goal-Directed Behaviour – Action to satisfy the need - Satisfaction of Need – hunger is satisfied thirst is quenched Homeostasis - Behavioral Responses to Heat and Cold o Ectotherms more dependent on behavioural devices o Changes in position, weight, colour, composition of fur - Endothermic Responses to Heat and Cold - Automatic internal response to deviations in temperature o Responses to lower temperatures PSY290H5S – Introduction to Physiological Psychology Lecture 5 – July 29, 2013  Shivering produces heat (internal mechanisms)  Body constricts blood vessels which takes blood away from the surface of the skin; therefore preserving heat (internal)  Thyroid gland releases an increase thyroid hormone, which increases metabolic activity (chemical reactions in the body) o Responses to higher temperatures  Blood vessels start to dilate (become bigger) then loses the heat through the skin (become red)  Sweating cools the skin through evaporation - Deviations in Human Core Temperature o Fever  If occurring because of bacteria/virus, a result can be pyrogens (chemical bi-products) which have the ability to cross the blood- brain barrier  Brain produces a response of increasing body temperature in order to kill any virus/bacteria o Heat stroke (hyperthermia)  If in a hot climate, and not drinking enough water to compensate because its cool in your hotel room  Body temperature is really high, even though you have no symptoms of being sick o Hypothermia  Body temperature drops - Brain Mechanisms for Temperature Regulation o Multiple mechanisms in order to safe guard the mechanisms for temperature regulation which is extremely important for survival o Preoptic area (POA) of the hypothalamus, anterior & posterior hypothalamus, and septum  Septum is located close to the corpus coliseum (close to the midbrain) o Proteins change in structure and function as a consequence of temperature - Temperature Regulation in Infancy o Relatively helpless in adapting to temperature because endothermic mechanism do not kick (develop like an adults until later) o (1) Ability to shiver is very immature (to generate that heat) o (2) The age related metabolism is very immature The Hypothalamus and Temperature Regulation - Located in the diencephalon - Hypothalamus, o Will start to regulate sweating, dilation of blood vessels - Posterior hypothalamus is responses to our responses to cold o Shivering - Hypothalamus receives a lot of information from the skin and thus spinal cord o The sensory information goes to the spinal cord, which sends a lot of information about the skin and temperature PSY290H5S – Introduction to Physiological Psychology Lecture 5 – July 29, 2013 The Body’s Fluids Are Held in Three Compartments - 2/3 of the body is contained in the intracellular fluid - 1/3 of the body is found within the extracellular fluid o Interstitial fluid – between cell fluid Osmosis Causes Water to Move** - What happens (for instance) someone is drowning in fresh water? - Or why is it recommended not to drink in the seawater? - Within the context of water, semi-permeable membrane o Helps to start making the analogy that there is a membrane between the intra and extracellular membrane - Equilibrium o Within the context of this slide, water can move through the semi-permeable membrane easily o However, the solutes (ie. Na), cannot move easily between the semi- permeable membrane o If you have a higher concentration of solution in the cylinder, water will move to the area of a high concentration of salt to maintain balance - If in the longer cylinder you add a lot of water o There will be a lower amount of concentration of solute, the water will move out of the longer cylinder into the beaker - If there is a high concentration of solute in one part of a two compartment system, water will go across membrane, and be attracted to high concentration of solute to dissolve it and attain equilibrium Thirst: Regulation of the Body’s Fluid - Intracellular and Extracellular Fluids o Extracellular fluid (33%) o Intracellular fluid (67%) - Osmosis Causes Water to Move PSY290H5S – Introduction to Physiological Psychology Lecture 5 – July 29, 2013 o Water moves from an area with lower concentration of solutes to an area with higher concentration o Hypotonic versus hypertonic (always think about the outside) - HYPOTONIC - If someone nearly drowns in fresh water o Take in a lot of fresh water, that doesn’t have a lot of salt o The extracellular fluid becomes hypotonic (Less concentration than the intracellular fluid) o The inside of the cell now has more solutes o Dangerous because if there is more solute inside the cell, all the freshwater (by osmosis), will go inside the cells where there is the additional of the solutes  can burst the cell o Treatment: give the person a lot of solutes - HYPERTONIC – If someone nearly drowns in salt water o Extracellular fluid becomes hypertonic (too much solute, salt) than the extracellular fluid o If the outside has a lot of solute, the inside of the cell will start losing water o The cells that are exposed will dehydrate and decrease in size because of the loss of water - The Role of the Kidneys o Excretes excess fluids and sodium o Important for filtering out the blood, done through the structure of nephrons o Filtered blood is functioning to prevent the idea of hypertonic and hypotonic - The Sensation of Thirst o Occurs as a result of osmotic and hypovolemic thirst  Osmotic thirst -  Hypovolemic thirst - Has to do with drops in blood volume o Double-depletion hypothesis - Mechanisms of Osmotic Thirst o Osmoreceptors located in the brain  Will respond to intracellular fluid changes  Neurons will start to change the rate of firing, based on fluid level changing o Organum vasculosum of the lamina terminalis (OVLT)  Locates around 3ed ventricle, and implicated to a large extend of this area  Detection of intracellular fluid changes (the most active) - Mechanisms of Hypovolemic Thirst o Baroreceptors measure blood pressure  If blood volume decreases, the blood pressure decreases  Blood flow detector – volume flow of the blood o Receptors in the heart and kidneys  Through baroreceptors, of heart and kidneys, you can detect bood flow and volume, pressure PSY290H5S – Introduction to Physiological Psychology Lecture 5 – July 29, 2013  Based on the blood flow, able to tell the volume of blood in a given area Detecting Osmotic Thirst - OVLT located close to the 3 ventricle that has ability to detect fluctuations of solutes in the blood - The blood brain barrier tends to be weaker, where the neurons have access to the blood supply relative to other neurons Thirst: Regulation of the Body’s Fluid - Hormones, Sodium, and Thirst o Cellular dehydration o Hypovolemia  Blood volume changes o Osmoreceptors o Baroreceptors o Posterior pituitary  o Kidneys o Adrenal glands Antidiuretic Hormone Begins a Sequence of Events Leading to Fluid Conservation - How does the pituitary gland play a role in managing thirst - Osmoreceptors detects intracellular dehydration - Baroreceptors – sense blood volume - All of this sends information to the pituitary gland, the posterior pituitary gland - It releases ADH which will: o Signal the kidneys to reduce the urine production o Stimulate the kidney to release the renin hormone - Renine will trigger the conversion of angiotensinogen (a blood protein) into: o Angiotensin 1 o Angiotensin 2 - Angiotensin 2 will constrict blood vessels to help maintain blood pressure and trigger the release aldosterone o Released from the adrenal gland - Aldosterone will send message to the kidney to retain sodium (rather than excrete it in the urine) o If there is not enough sodium in extracellular space, then the solution will become hypotonic PSY290H5S – Introduction to Physiological Psychology Lecture 5 – July
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