Neural & Hormonal Mechanisms (AQA A Level Psychology): Flashcards
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What is the role of the hypothalamus?
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What is the role of the hypothalamus?
It controls hormones, linking the nervous system to the endocrine system, and regulates homeostasis.
What did Hetherington and Ranson (1942) find?
Lesioning the ventromedial hypothalamus in rats caused them to become hyperphagic (overeat) and gain weight.
In the dual-centre model, the lateral hypothalamus is the 'feeding centre' or switch.
In the dual-centre model, the lateral hypothalamus is the 'feeding centre' or 'on' switch, initiating eating.
Define the ventromedial hypothalamus (VMH).
The VMH is the 'satiety centre' or 'off switch' in the dual-centre model, producing a feeling of fullness that stops eating.
What triggers the motivation to eat in the dual-centre model?
When glucose falls below a set point, glucose-sensing cells in the LH detect this and trigger eating behaviours such as searching for and preparing food.
How does the VMH signal that it is time to stop eating?
After eating, the liver provides glucose. Rising blood glucose is detected by cells in the VMH, which triggers satiety once past a set point.
True or False?
The LH and VMH work independently of each other.
False.
They work together in the dual-centre model to balance hunger and eating.
Define ghrelin.
Ghrelin is a hormone secreted from the lining of the stomach. Its concentration falls after each meal and rises until the next, acting as a marker of how long since the person last ate.
What happens when ghrelin is detected by the arcuate nucleus?
It signals the LH to secrete neuropeptide Y (NPY), a powerful hunger stimulant. Rats injected with NPY eat excessively even when sated.
Ghrelin also signals the pituitary gland to release .
Ghrelin also signals the pituitary gland to release growth hormones.
What did Wren et al. (2001) find?
Ghrelin given intravenously causes a short-term increase in food eaten. Circulating ghrelin roughly doubles before a meal and correlates with hunger.
Define leptin.
Leptin is a hormone produced by adipose (fat) cells and detected by the VMH, signalling that fat stores are high so that appetite decreases.
What happens to leptin when a person diets?
Fat is used up, fat cells stop producing leptin, blood levels fall, and the hypothalamus generates hunger.
In what two ways does leptin inhibit ghrelin?
It reduces ghrelin secretion in the stomach and suppresses ghrelin receptors in the neuropeptide Y system.
What did Nakazato et al. (2001) find?
Ghrelin injections stimulated feeding and weight gain in normal rats and in rats genetically deficient in growth hormone.
True or False?
Shiiya et al. (2002) found ghrelin levels were higher in obese people.
False.
Ghrelin was lower in obese people and higher in those with anorexia, supporting its role as an appetite stimulant.
What did Licinio et al. (2004) find?
People with a rare genetic inability to produce leptin lost over 40% of their weight on 18 months of leptin-replacement therapy, with food intake initially down 49%.
What real-world application does understanding these mechanisms offer?
Treatment possibilities for obesity, as we better understand how the nervous system and hormones regulate eating.
Why are neural and hormonal mechanisms only part of the picture?
Other factors such as biological rhythms affect eating. Rats become active and eat after dark regardless of when they last ate (Kraly et al., 1980).
True or False?
Leptin injections are a universally effective treatment for obesity.
False.
They have not been universally effective, so more research is needed on whether leptin aids weight loss or prevents weight gain.
Why does this explanation challenge free will?
It assumes eating is biologically determined by automatic hormonal signals, downplaying conscious decision-making and self-control.
Research into ghrelin and leptin is , using large samples to find general laws about eating.
Research into ghrelin and leptin is nomothetic, using large samples to find general laws about eating, but may overlook individual differences.
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