Appetite regulation Flashcards

1
Q

When do we percieve thirst?

A
  • Body fluid osmolarity is increased.
  • Blood volume is reduced.
  • Blood pressure is reduced.
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2
Q

Where are osmoreceptors found?

A

Hypothalamus, OVLT (Organum Vasculosum) and SFO (Subfornical Organ)

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3
Q

What is special about osmoreceptors?

A
  • Have an incomplete blood-brain barrier so they can detect changes in the blood
  • Cells shrink or swell in response to osmolarity and thus send signals to the ADH cells in the hypothalamus to alter ADH release
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4
Q

Why is thirst is decreased by drinking even before sufficient water has been absorbed by the GI-tract to correct the osmolarity of the blood?

A
  • Due to receptors in the mouth, pharynx and oesophagus the are involved.
  • Relief due to these receptors is short-lived (thirst only satisfied once osmolarity corrected).
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5
Q

What does angiotensin 2 do?

A

Induces thirst when blood volume and pressure is reduced

Acts by activating the SFO neurones.

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6
Q

What controls our appetite

A

The hypothalamus

  • You can modify the hypothalamic output voluntarily (like with breathing) but at times when you are not, the hypothalamus takes over
  • Recieves many inputs from letptin, ghrelin, gut hormones and normal input from other brain regions
  • It organises food intake and energy expenditure
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7
Q

Which 2 nuclei are involved in central control of appetite?

A

arcuate nucles and paraventricular nucleus

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8
Q

Arcuate nucleus

A
  • Located at the base of the brain, and has an incomplete blood brain barrier
  • Has two neuronal populations NPY/Agrp neurones and POMC neurones
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9
Q

What do NPY/Agrp neurones and POMC neurones do and where are they located?

A

NPY/Agrp neurons stimulate food intake and are located medially. POMC neurons inhibit food intake and are located more laterally.

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10
Q

How do POMC neurones inhibit food intake?

A

The MC4R (Melanocortin 4 Receptor) exists in the paraventricular nucleus and when stimulated, decreases food intake.

  • So POMC stimulates MC4R to reduce feeding.
  • POMC is broken down to alpha-MSH which acts on MC4R
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11
Q

Mutations affecting POMC and NPY/Agrp neurones

A

No NPY or Agrp mutations have been associated with appetite regulation in humans.

POMC deficiency and MC4R mutations cause morbid obesity

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12
Q

What are some higher brain centres involved in appetite?

A
  • Higher centres, the amygdala, vagus nerve and other parts of the hypothalamus can all
  • Dieting is an example of a higher brain function limiting appetite.
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13
Q

Leptin

A
  • A circulating hormone produced by white adipose tissue that is detected by the hypothalamus
  • Leptin binds to receptors in the hypothalamic circuits and stimulates anorexigenic behaviours (i.e. suppresses appetite)
  • Awell-nourished adult will accumulate body fat, which in turn increases leptin secretion and suppressing appetite
  • This feedback mechanism can become dysfunctional as leptin resistance is associated with obesity
  • The hormone is present but doesn’t signal effectively
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14
Q

Why does the hypothalamus alter neuropeptides?

A
  • Regulate food appetite (intake).

- Alter thermogenesis (expenditure).

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15
Q

Congenital leptin deficiency

A
  • Very rare and occurs due to mutations in the ob gene
  • Results in people that are severely hyperphagic and obese
  • These people however can be given leptin (unlike the leptin resistant obese)
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16
Q

Ghrelin

A
  • Ghrelin drives hunger before a meal and then drops after consumption.
  • Ghrelin affects the neurones in the arcuate nucleus:
    Stimulates NPY/Agrp neurones
    Inhibits POMC
    Thus increases appetite
17
Q

Peptide YY 3-36

A
  • Satiety hormone and is secreted from cells in the ileum and colon in response to a meal
  • Binds to hypothalamic receptors and reduces the perception of hunger and the urge to eat
  • Regulates short-term appetite control by suppressing eating behaviours
  • Secreted post-prandial and the levels secreted are proportional the the amount of calories in the meal
  • Affects the neurones in the arcuate nucleus:
    Inhibits NPY release.
    Stimulates POMC neurones.
    Thus decreases appetite.
18
Q

Why are we interested in obesity and body weight regulation?

A

obesity is associated with many co morbidites e.g. stroke, depression, sleep apnoea, MI, bowel cancer, diabetes, hypertension, gout and oesteoarthritis