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PSYCH 1XX3 Study Guide - Final Guide: Neuropeptide Y, Blood Sugar, Glycogen

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Joe Kim
Study Guide

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Glucose is the primary source of energy for the brain
Blood glucose levels regulate feelings of hunger and satiation
To keep your brain constantly supplied with energy, your body can store glucose
in the form of glycogen which can be released in between meals
Some glycogen is stored in the muscles, but the main supply is in your
liver where it can be readily converted back into glucose when your
circulating blood glucose levels are low
This glucose-glycogen balance is mediated by the liver and a pancreatic
hormone called insulin
The pancreas secretes insulin to promote the uptake of glucose by cells in your body
for immediate use, but also the stimulate storage of excess glucose as glycogen
The liver and pancreas help to buffer extreme swings in blood glucose levels
As this cycle continues and the time since your feast increases, your glycogen
reserves in the liver will decrease and send a status signal to the brain
At some point, the glucose and glycogen levels get too low and you will feel hungry
Between eating and sleeping, the glycogen stores are being depleted, so eating
breakfast increases blood sugar for now
Another morning breakfast cue comes from Neuropeptide Y (NPY)
High levels of activity in the hypothalamus, driven by NPY are associated with
increased appetite and food seeking behaviours
NPY affects feeding behaviour similarly in fish, reptiles, birds, and other
The liver can send signals to the brain that trigger satiety
Also if a dog is eating and you inject glucose into a vein that connects directly to
the liver, the dog will stop eating
However, into another vein that doesn’t connect to the liver, the dog will
continue eating
The liver monitors glycogen stores and blood sugar levels
Low blood glucose and low glycogen levels serve as signals of “hunger” while
high levels are signals of satiety

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As food moves from the stomach to the gut, the small intestine produces
Cholecystokinin (CCK), a hormone responsible for feelings of satiety
Receptors in the brain detect CCK, which serve as a signal to stop eating
Researchers administered CCK to rats leading to shorter than average meal
The rats that received CCK ate more total meal per day, so the total food
intake was the same for the control group and the CCK group
This shows that CCK is a short term satiety signal
CCK appears to regulate short-term feeding behaviours, like ending a meal, but
not long-term energy consumption
Long-term energy storage takes place in the form of fat (i.e., adipose tissue, an
endocrine organ)
Both short and long term mechanisms interact to regulate overall energy
balance and body-weight
Animals store most of their excess energy in the form of fat rather than glycogen
because fat has more than twice the energy that carbohydrates like glycogen
1g fat= 9 units of kilocalories. 1g carbohydrates= 4 kilocalories
Also, unlike glycogen, fat is found in virtually all parts of the body
A 70kg man has 1200 kcal of energy stored in glycogen, (enough to fuel
his activities for 12-18 hours), but he has 120 000 kcal stored in fat
(enough to live off of for a couple months
Adipose tissue secretes a hormone called leptin (involved in long term energy balance
and correlated with fat mass)
When leptin levels rise, they act on receptors in the hypothalamus to reduce
appetite, therefore food consumption decreases
Leptin production is controlled by the OB Gene
In knock-out mice, lacking an OB Gene, leptin production stops; in this
state, mice are missing a key hormonal signal to regulate appetite and
become extremely obese
These studies suggest that a contributing factor for obesity may involve
defective OB genes on receptors (although this is not supported by
clinical findings)
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