147: Appetite Regulation and Energy Expenditure

Question 1

Which neuropeptides are anorexogenic? (2)

How does leptin affect them?

Answer 1

POMC

CART

Leptin stimulates POMC, CART, which binds MC4R

• > satiety, decreased food intake
• Anorexogenic = decreased appetite

Question 2

What is the effect of a mutation in the MC4 receptor? (MC4R)

Answer 2

MC4R is part of the signaling pathway that tells us that we are full

If mutated, no feeling of fullness

• -> hungry all the time
• -> obesity

Leptin -> increased AgRP, POMC -> bind MC4R

Question 3

List the GI peptides that regulate appetite (5)

Answer 3

• CCK (satiety)
• GLP-1 (satiety)
• Amylin (satiety)
• PYY (satiety)
• Ghrelin (hunger)

They inform our brain about our food intake status

Question 4

When trying to lose weight, why is exercise less effective as a treatment than dietary restriction?

Answer 4

Net calorie burn is usually not significant enough to cause a meaningful difference in energy balance

(Net calorie burn = calories burned during exercise - what would have been burned just sitting on the couch)

65% of calories are burned from Resting Metabolic Rate

Only 15-30% through PA

Question 5

What is the primary hormone from fat cells that signals overall energy stores?

Answer 5

Leptin

• Produced by fat tissue
• Correlates with amount of body fat
• More fat cells→ more leptin released→ we have enough energy!
  
  • Decreased in fat→ decreased leptin→ panic! We are starving

Question 6

What condition is associated with leptin resistance?

What are the implications?

Answer 6

Obesity

• Fat stores increase and extra leptin is released
• However, receptors are saturated; we cannot sense extra body fat

Leptin is more effiecient at signaling depletion of energy stores (dropping when weight is lost) than signaling energy surplus (increasing when weight is gained)

Question 7

Which neuropeptides are orexigenic? (2)

How does leptin affect these hormones?

Answer 7

AgRP

NPY

Inhibited by leptin;
low leptin = increased AgRP, NPY -> increased appetitie

• Orexigenic = appetite stimulating
• AgRP and NPY inhibit MC4R (catabolic)
  
  • Leptin inhibits AgRP and NPY to remove the inhibition on MC4R

Question 8

Describe the hypothalamic response to a high fat diet

Answer 8

High fat diet ->

• Microglial and astrocyte activation
• -> Inflammation
• -> Resistance of CART and POMC to leptin signaling
  
  • CART/POMC are satiety signals (anorexigenic)
• -> hungry all the time

Question 9

Which hormone regulates day to day energy intake?

Answer 9

Ghrelin

• Regulatory sensor within the GI tract
• Causes us to feel hungry when energy intake is low
• Leptin regulated long term energy intake

Grehlin creates grouchy, hungry gremlins

Question 10

Which cells produce leptin?

Answer 10

Fat cells (adipocytes)

• Fat cells release leptin - function to signal long-term energy stores
• A decrease in leptin -> increased appetite
  
  • One reason people feel hungry all the time when they lose weight

Question 11

Which nutrients stimulate CCK, GLP-1, GLP-2, PYY, amylin release? (4)

Answer 11

These are the satiety signals.

Glucose

Amino acids

Short chain fatty acids

Long chain fatty acids

Question 12

What is the largest proportion of daily energy expenditure

Answer 12

Basal Metabolic Rate (BMR)

65% of energy expenditure

All the energy needed for cellular function/homeostasis