PS263 Lecture Notes - Lecture 9: Hyperinsulinemia, Somatostatin, Lipogenesis

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22 Feb 2017
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Hunger, Eating and Health
Digestion and Metabolism
-The benefits of eating are not realized until the food that we consume is digested.
-Digestion of food delivers energy to the body in three forms
1)Lipid (fats)
2)Amino acids (products of proteins)
3)Glucose (simple sugar broken down from complex carbohydrates)
-Since consumption is intermittent and energy use is constant the energy from food consumption is
stored in the form of fats (85%), glycogen (0.5%), and proteins (14.5%)
-Fat is the most efficient form of energy storage because it can store almost twice as much energy as
glycogen (at equivalent weight values)
-There are three phases of energy metabolism by the body.
1)Cephalic (preparatory) and absorptive phases level of insulin are high to promote immediate energy
use and storage.
-Glucagon levels are low to inhibit conversion of stored energy to useable energy during these two
phases. The reverse is true during the fasting phase. During this phase glucagon levels are high and
energy stores are "trapped" while insulin levels are low, inhibiting energy storage
Body Weight Regulation
-First influential study of the physiological basis of hunger was conducted in 1912 by Cannon and
Washburn. Washburn swallowed a balloon on the end of a thin tube. The balloon was partially inflated,
and a pressure gauge was attached to the other end of the tube.
-Each time the pressure gauge recorded a large stomach contraction, Washburn reported a hunger
pang. This was the scientific origin of the view that stomach contractions are a major factor in initiating
eating.
-If you remove the stomach from an experimental animal, or denervate the stomach (cut the part of the
vagus nerve that sends interoceptive input to the brain), that animal will still eat and maintain
bodyweight
Glucostatic Theory
-Research on feeding has been very strongly influenced by the idea that feeding is controlled by
deviation from two set points.
-One set point for blood glucose (glucostatic theory) which operates over a short term and one is a set
point for body fat (lipostatic theory) which operates over the long term.
-Based on a negative feedback system- changes in one direction of input to the system lead to
compensatory changes by the system
-Under normal conditions, blood glucose varies very little. In fact, our metabolism is designed to
maintain blood glucose at near constant levels by the release of the pancreatic hormones insulin and
glucagon.
-When feeding (the nutrient absorptive phase), insulin is secreted into the bloodstream which causes
glucose utilization (i.e reduces blood glucose).
-When fasting, glucagon is released which causes glucose to be released into the bloodstream (glycogen
in the liver is converted into glucose). If the Glucostatic theory were correct there would be large dips in
glucose levels prior to eating and then large increases of blood glucose after feeding
-Glucostatic theory would predict that these large dips in blood glucose prior to feeding would be the
impetus for feeding. This is not the case. While it is true that there is a small dip in blood glucose prior to
eating, it has been found experimentally that in order to cause feeding by dropping blood ucose
(achieved by increasing the levels of insulin), one needs to produce a very large drop in blood glucose
(50% as apposed to 6-7% which is about the average seen)
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