Lecture 32 - Feeding and weight control Flashcards
What are the short term satiety signals and what produces them?
Liver and stomach - CCK, Ghrelin
Vagus sends info to medulla to alter food intake - then goes to hypothalamus
Ghrelin stimulates
hunger - food intake
neuropeptide Y - does the same in the brain
What do adiposity signals do?
Long-term - keep the body weight the same
Leptin Insulin
What is CCK?
Satiety signal acts quickly
released in periphery but GIT. acts on the vagus nerve
antagonism of peripheral CCKa receptors increases food intake
what is Ghrelin?
Increases appetite and body weight
Predominately synthesised in the stomach
plasma levels inversely proporitional to BMI
Receptors located in hypothalamus
What is Leptin?
Secreted predominately from fat cells
plasma levels proportional to BMI and fat
Crosses BBB via a saturable process
receptors located in hypothalamus
inhibits food intake via CNS mechanism
What relevance does Leptin or Leptin deficiency have in obesity worldwide?
only relevant in a very small number of pateints - mainly other things
What is synthesised in the arcuate nucleus?
Stimulating appetite
NPY/AGRP neurons - inhibited by Leptin
inhibiting appetite:
POMC/CART - stimulated by Leptin
Both inhibit food uptake
What is NPY?
member of pancreatic polypeptide family
stimuates apetite, unlike other members of the family
Other members
Peptide YY - GIT
Pancreatic polypeptide - PANCREATIC ISLETs
Theses circulate and act acutely to inhibit food intake
NPY is one of the most potent…
appetite stimulating hormones known
stimulates feeling in satiated (full) animals - causes obesity
reduces energy expendature
Y1 and Y5 receptors are located
If leptin levels are low what happens in the hypothalamus?
less inhibition - more NPY being expressed
What is POMC?
Located in vairous regions in the brain but in particular the arcuate neurons -
undergoes post-translational processing to cause the producgtion of alpha-MSH
What is alpha-MSH?
released in PVN
inhibits food intake predominantly via MC4-receptor
Increases energy expendature
levels are regualted by feeding status and leptin (same as NPY)
Mutation in POMC or MC4R genes results in…
obesity - low levels of POMC
What is AGRP?
Endogenous antagonist at MC4R
inhibits a-MSH from binding to MC4R
-increases food intake
reduces energy expendature
level regualted by feed status and Leptin (again)
over-expressionof AGRP results in ____
obesity
do the diapgram which integrates all this,,
now
Circulating leptin levels are proportional to…
fat mass
What does Low Leptin (from decrease in fat mass) lead to…
NPY and AGRP increased
POMC decreased (decrease in a-MSH released) - increased body weight
What does High Leptin (from increase in fat mass) lead to…
NPY and AGRP decreased
POMC increased (increase in a-MSH released - decreased body weight)
What are the factors of obesity?
Genes sleep deprivation - increase in Grehlin food intake physical activity socioeconomic status cultural
While certain genes increase the susceptibility to obesity, the prevalence of obesity has almost ____ since 1980,
doubled
making purely genetic causes unlikely
What is the obesogenic environment?
Decline in physical activity
- decrease in rates of exercise
- increase in technology to complete activityof daily living, TV, computers
Food portion size - mistake quantity for quality
comsumption of suger-sweetened beverages
consmption of palatable energy-dense foods
- high fat/super
- cheaper (SES)
Bland foods not eaten in excess but what about palatable foods?
consumed after energy demands met
mjor contributing factor to obesity epidemic
the mesolimbic dompaminergic pathway activated in response to …
palatable food
VTA to NAc
important for natural reward
How is the reward sdystem invovled in appetite?
hnger enhances activation of meso-limbic pathway
leptin inhibits activity of VTA neurons
- VTA neurons express leptin receptor
Ghrelin stimulates activity of VTA dopaminergic neurons
- VTA neuron express ghrelin receptor
increases rewarding value of food
