Appetite regulation

Question 1

When do we percieve thirst?

Answer 1

• Body fluid osmolarity is increased.
• Blood volume is reduced.
• Blood pressure is reduced.

Question 2

Where are osmoreceptors found?

Answer 2

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

Question 3

What is special about osmoreceptors?

Answer 3

• 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

Question 4

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?

Answer 4

• 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).

Question 5

What does angiotensin 2 do?

Answer 5

Induces thirst when blood volume and pressure is reduced

Acts by activating the SFO neurones.

Question 6

What controls our appetite

Answer 6

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

Question 7

Which 2 nuclei are involved in central control of appetite?

Answer 7

arcuate nucles and paraventricular nucleus

Question 8

Arcuate nucleus

Answer 8

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

Question 9

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

Answer 9

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

Question 10

How do POMC neurones inhibit food intake?

Answer 10

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

Question 11

Mutations affecting POMC and NPY/Agrp neurones

Answer 11

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

POMC deficiency and MC4R mutations cause morbid obesity

Question 12

What are some higher brain centres involved in appetite?

Answer 12

• 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.

Question 13

Leptin

Answer 13

• 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

Question 14

Why does the hypothalamus alter neuropeptides?

Answer 14

• Regulate food appetite (intake).

- Alter thermogenesis (expenditure).

Question 15

Congenital leptin deficiency

Answer 15

• 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)

Question 16

Ghrelin

Answer 16

• 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

Question 17

Peptide YY 3-36

Answer 17

• 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.

Question 18

Why are we interested in obesity and body weight regulation?

Answer 18

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