What was discovered in the 1950s that sparked research?
A strain of mice that ate ravenously, gained weight, were inactive and had increased adipose tissue
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What did breeding experiments show about these mice?
They had two copies of the recessive allele, ob
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What did the dominant allele allow secretion of in mice?
Leptin
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What type of cells secrete leptin?
Adipose cells
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What do adipose cells do?
Fat storage
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What happens if the amount of adipose tissue in the body increases?
More leptin in bloodstream, more binds to receptors on cells in hypothalamus, long-term appetite inhibition and reduced food intake
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What is the target of leptin?
A group of cells in the hypothalamus
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What happened when ob/ob mice were injected with leptin?
Appetite declines, energy increased and body mass dropped
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What was the experiment done on humans to test leptin injections?
73 obese volunteers injected themselves with one or more leptin injections or a placebo. Double blind experiment until results were analysed and weight measured
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What were the findings of the human leptin injection experiment?
Injections caused skin irritation and swelling. 8 patients with highest dose lost 7.1kg average compared to 1.3kg loss of placebo participants. Any body mass lost was regained quickly and highest dose varied from loss of 15kg to gain of 5kg
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Why might obesity injections have failed in humans?
Humans different physiology to mice. Most cases of obesity due to hypothalamus target cells insensitive to leptin so increased dosage still caused a fail in response
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What is a possible cause of obesity?
Mutations in leptin gene
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What are problems with the leptin injection process?
Short-lived protein so has to be injected several times a day
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How does tiredness work?
Ganglion cells in retina detect if light or dark and send impulses to supra-chiasmatic nuclei in hypothalamus
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Where is melatonin secreted?
Pineal gland
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What do neurones in the SCN control?
Secretion of melatonin by pineal gland
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Melatonin levels are high...
In the evening/ night time
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Melatonin levels are low...
In the morning
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Which organ removes melatonin from the blood?
Liver
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What causes melatonin secretion to decline?
Age
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What happens if melatonin secretion declines with age?
Sleep patterns become more irregular
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What is a circadian rhythm?
A daily physical, mental or behavioural rhythm based on a 24hr cycle where you feel sleepy and sleep at night and energised in the morning
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