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Midterm 3 (Final) Chapter Notes P2.pdf

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McGill University
PSYC 211
Yogita Chudasama

PSYC211 Chapter 12 NotesNarrative Box Carrie was nursed poorly and she was thus underweight Her motor and cognitive development had also been slow Eventually she regained her appetite and had put on some weight She soon became heavier than she should be at her age and had developed compulsive behaviour skin picking collecting and lining up objects etc She also had a problem eating She would eat everything she could get her hands on at school and at home From her designated meals to leftovers to pieces of scrap food thrown into the garbage A specialist diagnosed her condition and limited her caloric intake to 1200 calories a day She was appointed a monitor to keep her on track at school Carrie has been diagnosed with PraderWilli syndrome caused by a deletion of several genes on chromosome 15 that are involved in the production of proteins that regulate the functioning of the hypothalamus This is caused by random accidents in the production of sperm cells IntroductionFor an organism to live in a possibly hostile environment it needs a barrier between its cells and the environment Within this barrier the internal uid of the cell has to be regulated For this regulation known as homeostasis to occur we have digestive respiratory circulatory and excretory systems Physiological Regulatory MechanismsPhysiological regulatory mechanism keeps constancy in the cell while the exterior of the cell face variability EX constant body temperature while exterior temperature changes 4 features of a regulatory mechanism1System variable the characteristic that is being regulated EX temperature2Set point the optimum value of the system variable the value we want to regulate to EX 37C3Detector device that monitors and signals when the system variable deviates from the set point 4Correctional mechanism mechanism that will restore the system variable to the set point Example room regulated by thermostatic heater Figure 121 System variable the air temperature of the room Detector thermostatSet point preset value for the desired temperatureCorrectional mechanism the coils of the heaterNegative feedback the effect produced by an action serves to diminish or stop that action EX the heater turns on to increase the temperature but turns off shortly after because it has felt the increase in heat Eating and drinking are correctional mechanisms that replenish the bodys water and nutrient supplies These ingestive behaviors are controlled by satiety mechanisms cessation of hunger or thirst Satiety mechanisms monitor the correctional mechanisms and not the actual system variables because it takes time for uid that is just ingested to replenish the system variable Figure 122Summary p 408409 Eating Some Facts About MetabolismWater balance can be achieved by the intake of two ingredients water and sodium chloride When we eat we must ingest enough carbohydrates fats amino acids vitamins and minerals not sodium Eating is more complicated than drinking Control of eating metabolism regulation of body weight environmental and physiological factors that begin and stop a meal and the neural mechanisms that monitor the nutritional state of our bodies and control our ingestive behaviour Eating disorders obesity and anorexia nervosa Why do we eat We eat to construct and maintain our own organs and obtain energy for muscular movement and body heat Building blocks and fuel Our cells needs fuel and oxygen to stay alive however our stomachs are sometimes empty We have two reservoirs that save our nutrients shortterm carbohydrates and longterm fats Shortterm in the liver cells and muscleslled with complex insoluble carbohydrate glycogenin the liver convert glucose to glycogen and store it with the presence of insulin peptide hormone When all the glucose is either used as fuel or converted into glycogen the glucose blood level falls and the pancreas and the brain detect this fall Pancreas response stop secretion of insulin start secretion of glucagon which turns glycogen into glucose Livers response soak up the excess glucose and store it as glycogen and the cycle repeats itself Reservoir used for the CNS your brain is fed by your liver which converts glycogen to glucose and sends it into the blood stream The neurons and the glia absorb and metabolize it When there is not enough glucose we usually eat more If we dont the brain taps into the longterm reservoir LongtermAdipose tissue fat tissue triglycerides contain glycerol and three fatty acidsFound beneath the skin and the abdominal cavityAble of absorbing nutrients from the blood and converting them to triglycerides to store them The cells can expand to an abnormally enormous size giant fat cellsKeeps us alive when we are fasting fat cells convert triglycerides into fuelWhen the brain uses the short term reservoir the other parts of the body use the fat tissue The reason why the other body parts leave the liver glucose to the brain is because glucose doesnt dissolve well in fatty tissues That means they need a transporter to get them through the double fat layer of cell membranes There are insulin receptors on these glucose transporters There needs to be insulin so that glucose can enter a cell The exception to this rule is the cells in the nervous system that dont have insulin receptors on the transporters Glucose can use the transporters in any condition to enter the cells Figure 1212Fasting phase metabolism that occurs when no food is available from the digestive system when glucose amino acids an fatty acid are derived from glycogen protein and adipose tissue Absorptive phase metabolism that occurs when food is available from the digestive system Glucose and amino acids are used up in this phase EX balanced meal of proteins carbohydrates and fats carbohydratesglucoseproteins amino acidsfatsfats1Absorb nutrients blood glucose increases The rise is detected by brain cells which causes the activity of the sympathetic nervous system to decrease and the activity of the parasympathetic nervous system to increase This cause the pancreas to stop secreting glucagon and start secreting insulin Glucose can now be used as fuel The extra glucose is converted into glycogen and is stores in the shortterm reservoirs The glucose left over is stored as fat cells in the longterm reservoir Some amino acids are used as building blocks and the rest are converted into fat 23Fats are stored in the longterm reservoir as adipose tissue Summary p 412 What Starts a MealRegulation of body weight balance between food intake and energy expenditure If energy expenditure is constant 2 mechanisms needed for control1Increase motivation to eat if the longterm reservoir is being depleted2Restrain food intake if we eat more calories than we need Signals from the EnvironmentOvereating is a biological evolutionary activity For our ancestors overeating when there was a lot of food assured they had enough in their longterm reservoirs to keep them healthy when food became scarce An empty stomach is the most obvious signal but there are psychological reasons why people eat hearing its time to eat seeing the time that you usually eat at etcSignals from the StomachThe gastrointestinal system releases a peptide hormone ghrelin controlling the release of the growth hormone Ghrelin increased with fasting and decreased with a large meal Blood levels of ghrelin increase right before a meal As Ghrelin increases food intake increases hunger Figure 1213Probable cause of overeating chronic elevation in the blood level of ghrelin it will stay high even after a meal The most common obesity surgery gastric bypass operation that suppresses ghrelin secretion The release of the hormone in normal organisms is controlled by the contents of the digestive system mostly the upper part of the small intestine and not by the availability of nutrient in the blood Ghrelin is not the only reason though because even after the gastric bypass surgery was successful and there is almost no ghrelin in the blood people still had the compulsion to eat food indicating that there is another activator of hunger Metabolic SignalsWe get hungrier and hungrier after not eating consecutive meals because there is aphysiological signal that is telling us we are tapping into our longterm reservoir
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