BioPsych Chap 12
what are the three phases of energy metabolism?
1) cephalic phase (prepatory phase) 2) absorptive phase 3) fasting phase
Why did Campfield and Smith's (1990) study not support the glucostatic thory?
1) it is a simple matter to construct a situation in which drops in blood glucose levels do not preced eating 2) the usual premeal decreases in blood glucose seem to be a response to the intention to start eating 3) if an expected meal is not served, blood glucose levels soon return to their previous homeostatic level 4) the glucose levels in the extracellular fluids that surround CNS neurons stay relatively constant, even when blood glucose levels drop 5) injection of insulin does not reliably induce eating unless the injection are sufficiently great to reduce blood glucose levels by 50%
what does insulin do?
1) promotes the use of glucose as the primary source of energy by the body (cephalic phase) 2) it promotes the conversion of bloodborne fuels to form that can be stored (glucose to glycogen and fat, and amino acids to proteins; absorptive phase) 3) it promotes the storage of glycogen in liver and muscle, fat in adipose tissue, and proteins in muscle (fasting phase)
what has been shown agains the effects of VMH and LGs lesions?
1) the primary role of the hypothalamus is to regulate the energy of the metabolism -bilateral VMH lesions increase blood insulin levels which increases lipogenesis and decreases lipolysis 2) many of the effects of VMH lesions are not attributable to to VMH damage -other areas are damaged, such as fibers that project from the near by paraventricular nuclei, when there is a VMH lesion
What two major effect has the discovery of the hunger and satiety peptides had on the search for the neural mechanisms of hunger and satiety?
1) the sheer number of hunger and satiety peptides indicates that the neural system that controls eating likely reacts to many different signals, not just to one or two 2) the discovery that many of the hunger and satiety peptisdes have receptors in the hypothalamus has renewed interest in th role of the hypothalamus in hunger and eating
what are the two important features found by Teitelbaum and Epstein about the features of the L syndrome?
1) they found that the aphagia was accompanied by adipsia 2) they found that LH-lesioned rats partially recover if they are kept alive by tube feeding
what percentage of U.S. adolescents suffer from anorexia nervosa?
3%
what peptides have been reported to reduce food intake?
CCK (cholecystokinin) , bombesin, glucagon, alpha-melanocyte-stimulating hormone, and somatostatin
melanocortins
a class of gut satiety peptides
aphagia
a complete cessation of eating (bilateral electrolyic lessions to the lateral hypothalamus can produce this
adipsia
a complext cessation of drinking
leptin
a hormone produced by fat cells that serves as a negative feedback signal for fat deposition
glucagon
a pancreatic hormone that promotes the release of free fatty acids from adipose tissue, their conversion to ketones, and the use of both as sources of energy
set-point assumption
a prescribed optimal level that when energy resources fall below causes hunger and eating; it is not consistent with the bulk of evidence
what are the three components of a set-pont system?
a set-point mechanism, a detector mechanism and an effector mechanism
homeostasis
a stable internal environment; internal physiological equilibrium that the body strives to maintain; requires sensory mechanism, response system, and a control center (e.g., thermostat)
cholecystokinin (CCK)
a stomach peptide that causes hungry rats to eat smaller meals when injected in their stomaches; it can also induce illness specifically a conditioned taste aversion in animals and nausea in humans
gastric bypass
a surgical treatment for extreme obesity that involves short-circuiting the normal path of food through the digestive tract so that its absorption is reduced
effector mechanism
acts to eliminate the deviations
fasting phase
all unstored energy from the previous meal has been used and the body is withdrawing energy from its reserves to meet its immediate energy requirements
adjustable gastric band procedure
an alternative to gastric bypass, which involves surgically positioning a hollow silicone band around the stomach to reduce the flow of food through it
lipids
are stored as fats; involved with long term energy reserves
why is fats rather than glycogen the primary mode of energy storage?
because a gram of fat can store almost twice as much energy as a gram of glycogen and because glycogen, unlike fat, attracts and hold substantial quantities of water
why where there two different set-point theories?
because glucose levels determine when we eat, and fat stores determine the amount of consumption over long-term (explaining why weight tends to be constant)
How was it possible for the gastrointestinal tract to give off satiety signals?
because the transplanted stomach had no functional nerves, the gastrointestinal saiety signal had to be reaching the brain through the blood, and because nutrients are not absorbed from the stomach bloodborne satiety signals could not have been a nutrient only some chemical releasd from the stomach
dynamic phase
begins as soon as the subject regains consciousness after the operation, and is characterized by several weeks of grossly excessive eating and rapid weight gain
hypotonia
below-normal muscle tone
serotonergic agonists as a treatment
can produce long-term satiety signals based on fat stores (such as fenfluramine and defenfluramine)
what are the characteristics of the fasting phase?
characterized by high levels blood levels of glucagon and low levels of insulin
what is the first step (of eight) in digestion?
chewing breaks up food and mixes it with saliva
what are the enviornmental influences for obesity?
cultural practices and beliefs (e.g., three meals a day), food that are inexpensive and tasty are high in fat and/or carbohydrates, "supersizing" due to cultural vaue of getting the best value, and a decrease in daily activity due to technological advances
set-point mechanism
defines the set point
detector mechanism
detects deviations from the set point
What differences are there in why some people become fat and others do not?
differences in consumption, differences in energy expenditures (differences in the basal metabolic rate, diet-induced thermogenesis, and nonexercise activity thermogenesis), and genetic differences
what is the sixth step (of eight) in digestion?
digestive enzymes in the duodenum, many of them from the gall bladder and pancreas, break down protein molecules to amino acids, and starch and complex sugar molecules to simple sugars. simple sugars and amino acids readily pass through the duodenum wall into the bloodstream and are carri ed to the liver
what are the two phases of the hyerphagia?
dynamic and static
how is the set point system a negative feedback system?
eating is turned on when energy is needed, and off when a set point has been reached
absorptive phase
energy absorbed into the bloodstream from the mean is meeting the body's immediate energy needs
what are the possible evolutionary influences for obesity?
evolutionary the fittest individuals were those who preferred high-calorie foods, ate to capacity when food was available, stored as many excess calories as possible in the form of body fat, and used their stores of calories as efficiently as possible; indivdual with out these abilities were unlikely to survive
hyperphagia
excessive eating; caused by large bilateral electrolytic lesions to the ventromedial hypothalamus (VMH)
visceral fat
fat stored around the internal organs of the body cavity; insulin levels are more closely correlated with it
subcutaneous fat
fat stored under the skin; leptin levels are more closely correlated with it
lipostatic theory
fat stores determine set-point (thought to account for long-term regulation)
what are the majority of energy stores?
fats
what is the seven step (of eight) in digestion?
fats are emulsified (broken into droplets) by bile, which is manufactured in the liver and stored in the gall bladder until it is released into the duodenum. emulsified fat cannot pass through the duodenum wall and is carried by small ducts in the duodenum wall into the lymphatic system
amino acids
from protein
glycogen
glucose from carbohydrates; involved with short term energy reserves; glucose is the body's primary immediate energy (only energy source for neurons)
glucostatic theories
glucose levels determine set-point (thought to account for meal initiation)
positive-incentive theory
humans and other animals are not normally driven to eat by internal energy deficits but are drawn to eat by the anticipated pleasure of eathing; it is the presence of good food or the anticipation of it, that normally makes us hungry, not an energy deficit
why are peptides released into the bloodstream?
ingested food interacts with receptors in the gastrointestinal tract causing the release of peptides
what two pancreas hormones control the flow of energy druing the three phases of energy metabolism?
insulin and glyucagon
What three major properties does serotonin-produced satiety have?
it caused the rats to resist the powerful attraction of highly palatable cafeteria diets, it reduced the amount of food that was consumed during each mean rather than reducing the number of meals, and it was associated with a shift in food preferences away from fatty foods
what does 5-HT agonists cause in humans?
it decreases the urge to eat high-calorie foods, consumption of fat, intensity of hunger, size of meals, and the number of snaks and bingeing
what does the properties of serotonin suggest?
it is suggested that it might be useful in combating obesity in humans
what is the major tenet of teh positive-incentive perspecitve on eating?
it is that eating is controlled in much the same way as sexual behavior: We engage in sexual behavior not because we have an internal deficit but because we have evolved to crave it
what does low levels of insulin cause in regards to glucose?
it makes it difficult for glucose to enter most body cells, which allows glucose to be saved for the brain
what might the reduction in blood glucose levels before a meal contribute to?
it may contribute to hunger, but changes in blood glucose does not prevent hunger or satiety
what does leptin appear to do in the body?
leptin levels and fat deposits are positively correlated, wich injections in obese mice decreasing eating and body fat; this is because leptin (the receptors for which are in the brain) serve as a negative feedback signal for fat deposition
what are the three forms of energy storages?
lipids, glycogen, and amino acids
arcuate nucleus
located in the hypothalamus and contains receptors for leptin and insulin
How is leptin related in humans?
most humans have high levels of leptin, but leptin injections don't reliably reduce body fat in obese humans (so there must be other feedback signals involved)
what is the eighth step (of eight) in digestion?
most of the remaining water and electrolytes are absorbed from the waste in the large intestine, and the remainder is ejected from the anus
what peptides have been studied that increase appetite?
neuropeptide Y, galanin, orexin-A, and ghrelin
NEAT
nonexercise activity thermogenesis; generated by activies sucha as fidgeting and the maintenance of posture and muscle tone
satiety peptides
peptides that decrease appetite
hunger peptides
peptides that increase appetite; tend to be synthesized in the brain, particularly in the hypothalamus
cephalic phase
prepatory phase; often begins with the sight, smell or even just th thought of food, and it ends when the food starts to be absorbed into the bloodstream; insulin released by the pancreas promotes glucose use and storage at this phase
What did Koopmans (1981) study using a second stomach find?
rats eat less when a 2nd stomach loaded with food is transplanted and kept in their bodies (kept by a noose around the pyloric sphincter); the decrease in their eatting is proportionate to both the caloric content and volume of the other stomach (even though no innvervation not nutrients are absorbed)
prader-Willi syndrome
results from an accident of chromosomal 15 replication, they experience insatiable hunger, little or no satiety, and an exceptionally slow metabolism (they act as if they are always hungy)
what is the second step (of eight) in digestion?
saliva lubricates food and begins its digestion
peptides
short chains of amino acids that can function as hormones and neurotransmitters
free fatty acids
stored in adipose tissue
what is the third step (of eight) in digestion?
swallowing moves food and drink down the esophagus to the stomach
negative feedback systems
systems in which reedback from changes in one direction elicit compensatory effects in the opposite direction
What does the Cannon and Washburn (1912) study suggest?
that stomach contractions lead to hunger, and distension to satiety, but even if you revome the stomach from an animal hunger is still experienced
positive-incentive value
the anticipated pleasure of a behavior
what did Campfield and Smith (1990) find about the blood glucose of rats before a meal?
the blood glucose level dropped sharply about 10 min before a meal
lipolysis
the breakdown of body fat to utilizable forms of energy
energy metabolism
the chemical changes by which energy is made available for an organism's use
gluconeogenesis
the conversion of protein to glucose
duodenum
the first segment of the small intestine, which normally carries food away from the stomach
according to the positive-incentive perspective what influences the positive incentive value of eating?
the flavor of the food (learned preference for flavors), what we have learned about the effects of the food (past experiences), time since your last meal, social influences (e.g., eating alone or in a group), and blood glucose levels
digestion
the gastrointestinal tract and the process of breaking down of food and the absorbing of its constituents
neuropeptide Y
the gut hunger peptide
what is the fourth step (of eight) in digestion?
the primary function of the stomach is to serve as a storage reservoir. they hydrochloric acid in the stomach breaks food down into small particles, and pepsin begins the process of breaking down protein molecules to amino acids
lipogenesis
the production of body fat
what is the fifth step (of eight) in digestion?
the stomach gradually empties it contents through the pyloric sphincter into the duodenum, the upper portion of the intestine, where most of the absorption takes place
What two regions of the hypothalamus has been linked to eating behavior control?
the ventromedial hypothalamus (VMH; staiety) and lateral hypothalamus (LH; feeding)
what can the assumptions of set point assumption be likened to?
thermostat-regulated heatin systems in a cool climate
what did the 1990's study of obese mice find?
these mice lacked leptin
what does bilateral lesions of teh noradrenergic bundle or the paraventricular nuclei produce?
they also produce hyperphagia and obesity, just as VMH lesions do
what do serotonin agonists do?
they consistently reduce a rats' food intake -even intake of platable food is affected-; it reduces the amount eaten per meal (rather than # of meals); and causes preferences to shift away from fatty foods
What are the problems with the set-point theories?
they don't account for the epidemic of eating disorders, there are inconsistencies with evolutionary pressures, eating is not ver sensitive to changes in body fat or individual's caloric status prior to a meal, and they fail to acount for factors such as taste, learning, and social influences on eating
ketones
used by muscles as a source of energy during the fasting phase; is converted from free fatty acids
What happened in the Cannon and Washburn (1912) experiment?
washburn swallowed an empty balloon tied to the end of a thin tube, then Cannon pumped some air into the balloon and connected the end of the tube to a water-filled glass U-tube so that Washburn's stomach contractions produced a momentary increase in the level of the water at the other end of the U-tube. Washburn reported a "pang" of hunger each time that a large stomach contraction was recorded
static phase
when consumption gradually declines to a level that is just sufficient to maintain a stable level of obesity
what was serotonin agonists used against obesity associated with?
with heart disease in some users
