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Oct 9 Lec 5.docx

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Michael Inzlicht

Oct 9 Lec 5 Homeostasis: • 3 main thermostats in nervous sys: o 1) hypothalamus = smallest set point o 2) brainstem o 3)spinal cord (has the largest set point = zone where temp is okay, 35-39) • Endotherm = maintains constant body temp, like a human • Ectotherm = body temp is same as enviro, like a reptile • Surface to volume ratio affects temperature reg o Higher the s.a. to volume ratio, harder it must work to maintain core temp  Ex. Small animals like a mouse have to work harder • Endotherms are more dependent on behv devices to maintain temp o Changes in position, weight, color, and composition of fur • Also internal responses: o Shiver, blood vessels constricting away from surface area of skin, thyroid hormone increasing. o OR for hot: perspiration, licking self, blood vessels dilating towards skin surface (flushed skin) Deviations in Human Core Temparature: • Fever • Heat stroke = hyperthermia • Hypothermia • Raynaud’s Disease: o Blood vessels constrict too extremely causing sudden spasms in arteries, often in fingers and toes in response to cold o More frequent in women • Preoptic area = responds to warm temperatures • Posterior hypothalamus = responds to cool temparatures • Infants are helpless in adapting to temp changes Thirst Regulation • Extracellular = 33% of our total volume of fluid comp • Intracellular = 67% of our total volume of fluid comp • Osmosis causes water to move from an area of low solute concn to high solute concn • Kidneys excrete excess fluids and sodium • Isotonic = equal concns on both sides • Hypertonic =higher concn of solutes, so water will move towards this • Hypotonic = lower concn of solutes • daily intake should be roughly equal to daily output • sensation of thirst = occurs as a result of 2 kinds of thirst: o 1) osmotic: drops in intracellular fluid, osmoreceptors  Organum vasculosum of the lamina terminalis (receptors in the OVLT) o 2) hypovolemic: drops in blood volume  Baroreceptors measure blood pressure  Receptors in heart and kidney  lower blood volume  lower blood pressure  less blood volume detected by receptors in heart and kidney initation of thirst  kidneys try to conserve remaining fluids (you won’t urinate that much) • when we are thirsty, a message is sent to the posterior pituitary gland to release ADH = antidiuretic hormone = vasopressin o this sends a message to kidneys to reduce urine prod to release renin o renin produces angiotensin II all we really need to know for renin o angiotensin II = constricts blood vessels, sends message to adrenal glands to release aldosterone which sends a message to kidneys to retain sodium • Low blood volume stimulates hunger for sodium as well • Drinking begins when angiotessin II acts on subfornical organ (SFO) • Drinking stops bc of fluid receptors in mouth, throat, digestive sys o Hyponatremia = electrolye disturbance
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