7 - FAT + EATING

Question 1

fat tissue is subject to long-term regulation, how?

Answer 1

• some animals show seasonal variations is body fat
• eg fattening up during spring (eg for hibernation)
• eg slimming down during winter
• can also find in a lab when food is constantly available (eg squirrels which also show hibernation like behaviour in the lab)

Question 2

what effect does the surgical removal of fat tissue have on weight?

Answer 2

• a transient effect
• if fat tissue is removed, it either regenerates
• or other fat tissues increase

^depends on type of fat

Question 3

statement:

fat tissue plays an active role on eating control

Answer 3

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Question 4

what hormone does fat cells produce?

Answer 4

leptin

• involved in eating behaviour
• also to store fat

Question 5

control function of leptin

Answer 5

empirical evidence:

• genetically modified mice with two copies of the obese gene (ob/ob mice)(instead of the usual 1 or 0)
• 2/3x heavier than normal mice
• have more/larger fat cells
• but cannot produce leptin
• brain monitors leptin levels
• leptin receptors in several cortical and hypothalamic areas
• leptin acts as a satiety signal
• injecting ob/ob mice with leptin (especially directly into the hypothalamus) = drastic weight loss (stop eating as much)(same thing didn’t happen with glucose)
• animals with defective leptin receptions also become obese (drastically overeats)

Question 6

fat tissue and eating control model

Answer 6

NEGATIVE FEEDBACK LOOK

• arcuate nucleus (hypothalamus) produces two types of chemicals (NPY and AGRP - signals to other nucleus)
• PVN (hypothalamus) has two types of neurons (NPY-receptors and MC-receptors)
• LH (lateral hypothalamus)
• NPY = activates NPY receptor neurons
• AGRP = inhibits MC-receptor neurons
• LH produces chemical = orexins

EATING BEHAVIOUR

• NPY receptor neurons activated
• MC receptor neurons inhibited
• orexins produced
• keeps eating = fat cells become full and produce leptin
• leptin = affect hypothalamus
  1-deactivates production of NPY and AGRP
  2-inhibits LH = no orexins
  3-leptin activates arcuate nucleus to produce aMSH which activates MC receptor neurons
  4-hypothalamus now produces CRH (corticotropin releasing hormone)
  5-NO EATING
  6-after some time, fat cells become empty due to emptying reserves and start again

Question 7

does leptin play a similar role in humans?

Answer 7

• no evidence of a similar role in humans
• no evidence of defective leptin production in most obese people (obesity rather associated with high leptin production)
• perhaps leptin insensitivity might cause obesity in humans? (but no clear evidence)
• likely to be multiple interacting reasons for obesity (cause overeating)

Question 8

what can prolonged severe caloric intake reduction cause?

Answer 8

• reduces leptin production
• reduces basal metabolic rate
• is for some animals a part of normal eating behaviour
• can result in death

Question 9

statement:

leptin levels drops before the body’s fat reserves have become depleted

• so in people with restricted energy intake - their leptin levels on a graph would be dropping without seeing their body fat reserves deplete in a number of days

Answer 9

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Question 10

information:

• humans can go for months on very small rations
• four days on 2/3 of our normal intake will not deplete our fat reserves

Answer 10

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