Week 9. Appetite Flashcards
What does leptin do?
decreases appetite
What are second order hormones?
LHA releases orexins –> stimulate appetite
PVN releases NPs that decrease food intake
Outline the function of ARC.
Arcuate nucleus.
- at the base of the hypothalamus, where the BBB is broken
- signals from periphery can enter
What does insulin do when directly added to brain?
decreases food intake
How is cephalic phase detected?
Stretch receptors in stomach detect empty stomach and low blood sugar
What does cholecystokinin (CCK) do?
- released from duodenum in response to fat
- reduces food intake by activating melacortin pathway in hypothalamus
Define the cephalic phase?
Pre injestion/hunger phase
When is peptide YY released?
Made in response to food entering GI tract
Produced at same time and in proportion to GLP1
How are leptin and insulin similar?
- both circulate in proportion to fat levels
- both decrease food intake
- body can become resistant to both
What are first order hormones?
- ARC contains two clusters of hormones
- ones that secret NPY –> increase appetite
Neurones that secret melanocortins - suppress appetite
What is neuropeptide Y(NPY)?
- potently stimulates food intake
- but knocking out gene has no effect on appetite
Outline the function of PVN.
Paraventricular nucleus.
- integrating centre
- most number of peptides regulating appetite produced here
What is the intestinal phase?
Induction of satiation
Why do diets fail?
10 week low calorie diet resets homeostatic peptides.
- increase in ghrelin
- decrease in satiety hormones
- 30% increase in weight after diet
Outline the function of VMN.
Ventromedial nucleus.
- largest nuclei
- satiety centre
- site of action for peptides
What is ghrelin and when is it released?
- secreted by gastric mucous in empty stomach
- peaks when fasting just before a meal
- function is to ensure you eat enough fat
Outline the function of LHA.
Lateral hypothalamic area
- only one that produces peptides that cause hunger
What is the pattern of hunger. Define each stage.
- hunger - desire to eat (anything)
- appetite - desire to eat specific food or nutrient
- Satiation - desire to stop eating at the end of the meal
- satiety - delaying the next meal
Where is leptin produced?
adipose tissue
Where does the input into the hypothalamus come from?
- neural input from cerebral cortex and limbic system
- peptide hormones from GI tract
- adipocytokines from adipose
What is Agouti related peptide?
- stimulates food intake
- antagonist in melacortin system
What compounds are related to hedonic behaviour?
Dopamine –> mood and addiction. Associated with wanting sweet things
Serotonine –> feel good hormone.
Endocannaboids –> pain, appetite, memory
- antagonists will reduce food intake
What is alpha melanocyte stimulating hormone (αMSH)?
- inhibits food intake
- agonist in melacortin system
Which nutrients are the most satiating?
Protein - most satiating
complex carbohydrate - satiating
fat - makes you want to eat more
What hormone imbalances exist in obese people?
Less PYY satiation hormones.
Unclear pattern of ghrelin.
What are the motor events of the cephalic phase?
- relaxation of sphincter
- gall bladder contractions
Name six things about glucagon like peptide 1 (GLP1)
- proglucagon gene
- expressed in pancreas –> cleaved to form glucagon
- also expressed in intestinal L cells
- decreases food intake by reducing gut motility
- encourages energy expenditure
What happens to leptin and ghrelin in obese people?
Leptin and ghrelin –> homeostatic control of appetite
- in obese people, leptin stops working but ghrelin doesn’t
Which receptor in the brain does insulin bind to?
tyrosine kinase receptors
What is the gastric phase?
Consumption stage, release of gut and neuro peptides
What do insulin antibodies do to appetite?
increase it
What is the glucostatic theory?
- glucose levels ultimately control feeding and satiety centre
What are the secretory events of the cephalic phase?
- saliva
- pepsinogen
- pancreatic enzymes
What is the lipostatic theory?
- level of body fat regulates feeding and satiety
What is the difference between insulin and leptin?
Insulin:
Weight gain –> increased insulin and resistance
Weight loss –> decrease in insulin
Leptin:
As weight decreases, leptin dissociates from fat levels
- drop in leptin far greater than drop in body fat
How to peripheral signals interact with each other?
Release of ghrelin –> hunger –> stretch receptors in stomach activated –> parasympathetic nervous system –> increase in gastric secretions –> food –> stomach lining stretches –> CCK released
