Neural and Hormonal Mechanisms the Control of EB

• Neural Mechanisms and role of hypothalamus

  • Involved in maintaining homeostasis – balancing bodily processes within certain limits
  • Homeostasis regulates the level of glucose in the blood
  • Glucose is the most basic form of sugar and the body’s main energy source
  • Glucose-sensing neurons in the hypothalamus can detect changes in glucose levels
  • The hypothalamus can then regulate glucose levels by releasing either insulin or anti-insulin hormones
• Dual-centre model of eating:

  • This model suggests that two structures of the hypothalamus provide homeostatic control:
  • Lateral Hypothalamus (LH)
  • The ‘on switch’ for hunger
  • Ventro-medial hypothalamus (VMH) 
  • The ‘off switch’ of eating behaviour 
• Lateral hypothalamus- LH: on switch

  • Contains cells that detect glucose levels
  • LH is activated when glucose levels fall below certain level
  • This causes individual to become hungry – increases motivation to eat
  • The neurotransmitter NPY is also linked to the LH. It is a powerful stimulant of hunger. Rats injected with NPY directly into hypothalamus eat excessively and become obese
• Ventro-medial hypothalamus (VMH) - off switch

  • Eating food provides glucose, so blood glucose levels increase 
  • These glucose levels are detected by cells in the VMH
  • The VMH is activated if glucose levels pass a set point. 
  • This also stops the LH from working so you stop eating
  • The individual feels full and stops eating
  • Damage to the VMH is linked to overeating past the point of satiety (feeling full)
  • Research found that tumour on woman’s VMH led to her weight doubling in two year
• Hormonal mechanisms - role of ghrelin:

  • Ghrelin is a hormone secreted by the stomach
  • It’s closely related to how empty our stomach is 
  • More ghrelin is released the longer we go without food
  • When the hypothalamus detects ghrelin levels have passed a certain point, NPY is released which stimulates hunger and motivates you to eat
• Hormonal - role of leptin:

  • Leptin is a hormone secreted by fat cells
  • It is an appetite suppressant (stops you feeling hungry)
  • Leptin levels in the blood increase along with fat levels
  • This increase is detected by the brain by the VMH
  • Once levels increase beyond a certain point, the individual stops eating and feels full
  • Research shows that a rare genetic conditions, in which individuals are unable to produce leptin naturally, is associated with severe obesity
• Neural and hormonal mechanisms :

  
• A03:

  • A strength of the dual-centre model is that there is research to support it from studies on rats
  • Research shows that by lesioning the VMH of rats, they became hyperphagic (they would overeat) and eventually became severely obese
  • When researchers have lesioned the LH of rats, the outcome was aphagia (not eating)
  • This supports the model because it suggests that the LH is the ‘on switch’ for eating and the VMH is the ‘off switch’
• A03:

  • A limitation of dual-centre model explanations of eating behaviour is that it is oversimplified
  • Valassi et al. (2008) point out that research continues to reveal more neural and hormonal influences on eating behaviour
  • For example, a hormone called CCK produced in the intestine may be an even more powerful appetite suppressant than leptin
  • Therefore, the dual-centre model does not accurately reflect the true complexity of how eating behaviour is controlled
• A03:

  • A limitation of neural and hormonal explanations in the control of eating behaviour is that they ignore social and cultural factors
  • The LH (on switch) only identifies drops in glucose levels in ‘emergency’ conditions when energy levels are severely low
  • Normal meal onset is much less controlled by neurochemical factors and is usually initiated by social and culture factors related to lifestyle (e.g. Meal times)
  • Therefore, a purely biological approach to understanding eating behaviour tends to ignore potentially important non-biological factors that may be more influential
• A03:

  • A strength of research into neural and hormonal mechanisms in eating behaviour is that this increased understanding can lead to treatments for obesity and anorexia
  • For example, the fact that researchers know that leptin suppresses the appetite means if someone has low leptin levels they can provide treatment to regulate leptin levels
  • This means they can treat individuals who may have genetically determined leptin deficiencies and treat their obesity
  • This would help the wider economy as it would reduce health costs for the NHS regarding health problems linked to obesity