lecture 25 - control of energy balance

Question 1

How is food intake regulated?

Answer 1

Signals from gut

Hormones

Bloodborne signals related to energy stores

Psychological factors

Question 2

How is the hypothalamus involved in controlling food intake?

Answer 2

Hunger: the need to eat (stimulate orexigenic pathway)

Satiety: the feeling of fullness (stimulate anorexigenic pathway)

Regions of the hypothalamus include
Arcuate nucleus (ARC)
Lateral hypothalamic area (LHA)
Ventromedial nucleus (VMN)

ARC contains 2 distinct sets of neurons
NPY/AgRP
POMC/CART

NPY/AgRP act on LHA to increase feeding (orexigenic)

POMC/CART act on the VMN to reduce feeding (anorexigenic)

Question 3

How are signals from the gut involved in controlling food intake?

Answer 3

Activation of stretch receptors from stomach distension (vagal nerve) - stomach distends from filling up with food

Nutrients from food

stimulates anorexigenic pathway

Question 4

How are hormones involved in controlling food intake (short-term)?

Answer 4

Released during food absorption
Cholecystokinin (CCK)
Insulin

Released in the fasting state
Ghrelin (Ghr) - stimulates orexigenic pathway
Glucagon
Adrenaline

Question 5

How is leptin involved in controlling food intake (long-term)?

Answer 5

Related to amount of stored energy

Produced by adipose tissue (increase fat stores, increased leptin produced)

Reduces feeding by supressing NPY and stimulating CART neurons

Levels high during obesity (leptin resistance? doesn’t have effect)

Question 6

How is obesity treated?

Answer 6

Behavioural:
Diet
Exercise

Pharmacological:
Phentermine, Phendimetrazine, Diethylpropion - no longer legal - stimulants - amphetamines
Orlistat - only prescribed if obese, lipase inhibitor - fats can’t be broken down so aren’t absorbed into the bloodstream and are passed in the faeces

Surgical (bariatric surgery)
Malabsorptive surgery - take away parts of small intestine so less absorption can take place
Restrictive surgery (gastric band or bypass) - reduce size of stomach, stimulate stretch receptors earlier so full earlier
Bypass is band and removing part of small intestine
Surgery only offered if BMI over 40