neural and hormonal mechanisms in the control of eating behaviour Flashcards
role of the hypothalamus
crucial role in integrating the nervous and endocrine system
involved in maintaining homeostasis - balancing of bodily processes within certain limits
regulates the level of glucose in the blood
glucose - most basic of sugars and body’s main source of energy
fluctuations in blood glucose concentration are detected by glucose sensing neurons in the hypothalamus
can then regulate glucose levels by influencing the output of insulin and anti-insulin hormones
insulin and glucagon are secreted from the pancreas and play a key role in maintaining blood glucose homeostasis within a narrow range of values
dual centre model of eating behaviour
two areas of the hypothalamus provide homeostatic control over blood glucose levels
lateral hypothalamus (LH)
feeding centre - on switch
contains cells that detect levels of glucose in the liver
activated when glucose levels fall below a certain level
causes an indicuals to become hungry and triggers to motivation to eat
along with behaviours such as searching for and preparing food
secretion of a hypothalamic neurotransmitter - neuropeptide
closely associated with hunger and a reduction in physical activity
powerful stimulate of hunger
rats injected with NPY directly into the hypothalamus will eat excessively and evtually become obsessed as the injection continue
ventromedial hypothalumus (VMH)
satiety centre - off switch
eating food provides the body with glucose circulating in the blood stream and stored in the liver as glycogen rose again
these levels are detected by cells in the VMH
acitivity in the VMH is then triggered once glucose levels increase part a set point
LH activity is inhibited at the same time
individual become satiated - feel full and stop eating
damage to the VMH is linked with continued eating past the point of satiety
Reeves and Plum
reported a case of a women whose weight more than doubled in a 2 year peirod
post-mortem revealed that she had a tumour on her VMH which caused its normal stop eating function to fail
role of ghrelin
hormone secreted by the stomach
hormonal marker of how long since we have last eaten
the amount produced is closely related to how empty out stomach is
more ghrelin is released the longer we go without food
levels are detected by receptors in part of the hypothalamus - arcuate nucleus
when levels rise above a set point the arcute nucleus sends signals to the lateral hypothalamus to secrete NPY
known to be an appetite stimulus
wren- intravenously ghrelin caused short term increase in the amount of food eaten
amount of ghrelin circulating in the bloodstream closely correlates with subjective feelings of hunger
the role of leptin
hormone produced by adipose (fat cells)
levels of leptin in blood increase along with fat levels
detected in the brain by the VMH
as leptin is an appetite suppressant it contributes to the VMH satiety mechanism
once levels have increased to a certain amount the individual feels fill and stops eating
Licinio et al
studied an extremely rare genetic condition in which indouals are unable to procedure leptin naturally
associated with severe obesity
treatment involves leptin-replacement therapy over 18 month peirod
found that this led to an average weight loss of more than 40% and a reduction of food intake initially of 49%
strength
research support for dual centre model
lesion study with rats
surgical wounds are created in various strategic brain areas
Hetherinhgton and ransom
showed that ‘lesioning of the VMH of rats caused these animals to become hyperphgic(overeat)
eventually severely obsess
Anad and Brobeck
lesioned the LH of rats and the outcome was aphagia (starvation)
illustrates the homeostatic nature fo a mechanism
two brian centres with opposing functions as predicted by the model
limitation
oversimplified models
Valassi et al
highlight the tole of a hormone called CCK
produced in the upper intestine
activates the nerve that sends signals from the gastrotestinal tract to the hypothalamus
these signals indicate satitiet and contribute to the stop eating mechanism
CCK may be a more powerful appetite suppressant than leptin
shows that the true nature of neural and hormonal control of eating is complex
limitation
social and cultural factors underplayed
purely homeostatic view underplays social and cultural influences
woods
the view that LH defending centre always detects falls in blood glucose levels and stimulated hunger is outdated
only occurs in emergency conditions of severe energy deprivation
normal everyday eating neurochemsity plays a much lesser role
onset of eating is more controlled by social and cultural factors related to lifestyle
suggest a biological approach to understanding eating heavier ignores potentially importnat nonbiological factors that may be more influential
