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Chapter 12

PSYC 211 Chapter Notes - Chapter 12: Adipose Tissue, Nucleus Accumbens, Cholecystokinin

Course Code
PSYC 211
Yogita Chudasama

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Chapter 12: Ingestive Behaviour
Notes taken by: Ashley Brown
Contact for mistakes: Ashley.brown@mail.mcgill.ca
Physiological Regulatory Mechanisms
Homeostasis: the process by which the body’s substances and characteristics (such as
temperature and glucose level) are maintained at their optimal level
Ingestive behaviour: eating or drinking (intake of food, water, and minerals)
A physiological regulatory mechanism is one that maintains the constancy of some
internal characteristic of the organism in the face of external variability
- ex: keeping body temperature constant despite changes in ambient
- Contains four essential features:
o System variable: a variable that is controlled by a regulatory
mechanism, for example, temperature in a heating system. AKA the
characteristic to be regulated
o Set point: the optimal value of the system variable in a regulatory
o Detector: a mechanism that signals when the system variable deviates
from its set point
o Correctional mechanism: the mechanism that is capable of changing
the value of the system variable
- Negative feedback: a process whereby the effect produced by an action
serves to diminish or terminate that action; a characteristic of regulatory
Ingestive behaviours are controlled by satiety mechanisms and by detectors that monitor
the system variables
- satiety mechanisms are a brain mechanism that causes cessation of hunger or
thirst, produced by adequate and available supplies of nutrients or water
o they monitor the activity of the correctional mechanism, not the
system variable themselves
Eating: Some Facts About Metabolism
We can achieve water balance by the intake of 2 ingredients: water and sodium chloride
Eating needs to obtain adequate amounts of carbohydrates, fats, amino acids, vitamins,
and minerals (other than sodium).
Control of eating involves: metabolism, regulation of body weight, the environmental and
physiological factors that begin and stop a meal, and the neural mechanisms that monitor
the nutritional state of our bodies and control our ingestive behaviour.

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Reasons we eat: to construct and maintain our own organs and to obtain energy for
muscular movements and for keeping our bodies warm.
Two reservoirs that store nutrients to keep the cells of the body nourished when the gut is
empty: a short-term one and a long-term one
Short-term reservoir is located in the cells of the liver and the muscles
- filled with a complex insoluble carbohydrate called glycogen which is oftern
referred to as animal starch
- cells in the liver convert glucose into the polysaccharide glycogen and then
store it. This process is stimulated by the presence of insulin
o insulin is a pancreatic hormone that facilitates the entry of glucose and
amino acids into the cell, conversion of glucose into glycogen, and
transport of fats into adipose tissue
o When glucose and insulin are present the body uses some glucose and
fuel and converts the rest to glycogen for use later
- This reservoir is used primarily for the CNS
o When glucose from the liver reaches the CNS it is absorbed and
metabolised by neurons and glia
The fall in glucose is detected by cells in the pancreas and in the brain
- pancreas responds by stopping its secretion of insulin and starting to secrete
glucagon which promotes the conversion of liver glycogen into glucose
- this causes the liver to release glucose from its stores
Long-term reservoir consist of adipose tissue
- filled with triglycerides which are the form of fat storage in adipose cells
o consist of a molecule of glycerol (a soluble carbohydrate, also called
glycerine. Can be converted to glucose by the liver) combined with
three fatty acids (stearic acid, oleic acid, and palmitic acid)
- adipose tissue is found under the skin and in various locations in the
abdominal cavity
o consist of cells that are capable of absorbing nutrients from the blood,
converting them to triglycerides, and storing them
these cell can expand enormously (difference in obese and
normal weight people is that determined by the amount of
triglycerides their fat cells contain)
- keeps us alive when we are fasting
o as we use the contents of our short term reservoir, fat cells convert
triglycerides into a form that we can use
o when you wake up with an empty digestive system the cells of the
body (not CNS) are living off fatty acids to spare the glucose for the
o sympathetic nervous system (which is primarily involved in the
breakdown and utilization of stored nutrients) increases in activity

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when digestive system is fasting esp the ones that innervate adipose
tissue, the pancreas, and the adrenal medulla
o all three effects (direct neural stimulation, secretion of glucagon, and
secretion of catecholamines) cause triglycerides in the long-term fat
reservoir to be broken down into glycerol and fatty acids
o fatty acids can be directly metabolized by cells in all of the body but
the brain which needs glucose
Insulin not only causes glucose to be converted to glycogen but has other functions like
controlling the entry of glucose in cells
- glucose is polar, so it can not pass through the nonpolar membranes of cells
without glucose transporters
o these transporters contain insulin receptors that control its activity:
only when insulin is bound to them can glucose come into the cell
o cells in the brain don’t need to have insulin bound for these
transporters to work so glucose can enter without insulin present
Fasting phase: the phase of metabolism during which nutrients are not available from the
digestive system; glucose, amino acids, and fatty acids are derived from glycogen,
protein, and adipose tissue during this phase
- see fig 12.12, page 411
- a fall in blood glucose level causes pancreas to stop secreting insulin and start
secreting glucagon
- absence of insulin cells of body can no longer use glucose only CNS
- presence of glucagon/absence of insulin liver starts drawing on the short-
term carbohydrate reservoir and converts glycogen into glucose
- fat cells start breaking down triglycerides into fatty acids and glycerol
o body uses fatty acids
o liver converts glycerol to glucose for the brain
- if fasting is prolonged, protein, esp that found in muscle, will be broken down
into amino acids which can be metabolized by everything but the CNS
Absorptive phase: the phase of metabolism during which nutrients are absorbed from
the digestive system; glucose and amino acids constitute the principal source of energy
for cells during this phase and excess nutrients are stored in adipose tissue in the form of
- as we start absorbing the nutrients, levels of blood glucose rise which is
detected by cells in the brain which causes the activity of the sympathetic
nervous system to decrease and the activity of the parasympathetic nervous
system to increase change tells the pancreas to stop secreting glucagon and
begin secreting insulin insulin allows all cells of the body to use glucose as
fuel extra glucose is converted to glycogen which fills the short-term
carbohydrate reservoir if glucose still left its converted to fat and absorbed
by fat cells
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