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bio ch 12 .doc

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York University
PSYC 3250
Pauline Charlton

Ch 12 ingestive behaviour Homeostasis regulation of fluids that bathes our cells Ingestive behaviour includes intake of food water and minerals like sodium Physiological regulatory mechanisms Regulatory mechanisms are used to keep our body temperature regular despite changes of external temperaturethere are 4 features of a regulatory systemSystem variable variable which is controlled by the regulatory mechanism ie Temperature in the heating system Set pt the optimal value of the system variable in the regulatory mechanism Detector monitors the value of the system variable Correctional mechanism restores the system variable to the set ptuses a ve feedback to determine when the body is becoming too hot or cold Both drinking and eating requires regulatory mechanism and correctional mechanisms when the body is depleted of water or nutrients Satiety mechanisms are used in order to monitor the correlational mechanisms but not the system variable to initiate a stop when sufficient amounts of drinking or eating occurs DrinkingSome facts about fluid balance Body has 4 major fluid compartments 1 intracellular and 3 extracellular fluidsof body water is found in intracellular fluids the fluid part of cytoplasm of cells 13 is found in extracellular fluids which includes the intravascular fluid blood plasma CSF less than 1 of fluid and interstitial fluid seawater which bathes the cells The intracellular and intravascular fluids must be kept between strict limits Intracellular fluid is controlled by the of solutes in the interstitial fluids Normally the difference is isotonic or balanced so HO doesnt move in or out of the cells Hypertonic when the interstitial fluid looses water so the cell water will be pulled out Hypotonic when interstitial fluid becomes diluted HO moves into the cellsHypovolemia when blood volume falls too low the heart is unable to pump the bloodeffectivelywhen this happens the muscles contract blood into smaller veins and arteries so it has less space to flow in Two types of thirst The body can loose HO by evaporation pure distilled HO or by sweating sweating looses both HO and Na so a need for both is requiredOsmometric thirst Occurs when solute of the interstitial fluid increasesresults in a shrinkage of cells Osmometric refers to detectors responding to the changes in the interstitial fluid whereas osmosis is the movement of the water from a semipermeable membrane from a region of low solute to high soluteVerney suggested idea of osmoreceptors shrinkage of cells would result in a change in firing rate of their neurons and sends signals to other areas of the brain Osmoreceptors are located in the circumventricular organs the OVLT and SFOthese two organs are located in many areas of the brain including the area postrema OVLT and SFO are located outside of the bloodbrain barrier so substances in the blood can pass into the interstitial fluid to the organs easily Volumetric thirst Occurs when volumes of blood plasma intravascular volume decreases Evaporation causes both volumetric and osmotic thirst whereas hypovolemia caused by diarrhea loss of blood and vomiting only deplete the intravascular fluids Volumetric thirst leads to a salt appetite detectors used for initiating this thirst includes angiotensin in kidneys and atrial baroreceptors in the heart and large blood vessels
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