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PSYC 211
Yogita Chudasama

PSYC 211 FINAL NOTES 4/19/2012 12:30:00 PM CHAPTER 12 – INGESTIVE BEHAVIOUR Regulation of fluid that bathes our cells – homeostasis Ingestive behavior: intake of food, water and minerals such as sodium. A regulatory mechanism contains four essential features: the system variable (characteristic to be regulated), a set point (the optimal value of the system variable), a detector that monitors the value of the system variable, and a correctional mechanism that restores the system variable to the set point When a sufficient amount of drinking occurs, the satiety mechs stop further drinking in anticipation of the replenishment that will occur later. Drinking  The body contains four major fluid compartments: one compartment of intracellular fluid (2/3 of body’s fluid) and three of extracellular fluid (intravascular fluid – blood plasma, CSF, interstitial fluid – isotonic with intracellular fluid) o If interstitial fluid loses water (hypertonic) and water pulled out of cells  Hypovolemia – low volume of blood (loss of blood, vomiting and diarrhea) – adjustments for loss of blood volume by contracting the muscles in smaller veins and arteries, thereby presenting a smaller space for the blood to full, but this correctional mech has definite limits  Thirst – osmometric and volumetric – moisture lost through evaporation is pure distilled water.  Osmometric thirst is when solute concentration of interstitial fluid increases. Detectors = osmoreceptors and firing rate affected by level of hydration – located in lamina terminalis which has two circumventricular organs – OVLT and SFO and are located outside BB barrier o Eating salty meal – pure osmometric thirst o Thirsty subjects had activity in ACC and lamia terminalis but when allowed to drink, activity decreased only in ACC therefore ACC reflects thirst o Evaporation produces both osmometric and volumetric thirst  Volumetric thirst – kidneys detect decreases in flow of blood to them – when decreased, cells in there secrete renin which enters blood and catalyzes conversion of angiotensinogen into angiotensin – active form = AII – stimulates secretion of hormones by posterior pituitary and adrenal cortex causing kidneys to conserve water and sodium and increased blood pressure through constriction of arteries – initiates both drinking and salt appetite o Hypertension (high blood pressure) caused by oversecretion of renin – Captopril blocks enzyme that converts AI to AII (treatment) o Aldosterone, steroid hormone, that stimulates kidneys to retain sodium o Atria passively filled with blood being returned from the body by the veins. When the volume of the blood plasma falls, the atria become less full and the stretch receptors within them will detect this change  Neural Mechs of Thirst o Sensory info from baroreceptors in atria sent to nucleus of the solitary tract – sends efferent axons to lamina terminalis o Subfornical organ is site at which blood angiotensin acts to produce thirst – very low doses of angiotensin inje
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