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Chapter 11
Ingestive Behavior
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• Chapter 11 Outline
• Physiological Regulatory Mechanisms
• Drinking
• Eating: Some Facts about Metabolism
• What Starts a Meal?
• What Stops a Meal?
• Brain Mechanisms
• Eating Disorders
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• Physiological Regulatory Mechanisms
• Object – maintain the ____________________.
• ________________
• The process by which the body’s substances and
characteristics (such as temperature and glucose
level) are maintained at their _______________.
• Ingestive behavior
• Eating or drinking.
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• Physiological Regulatory Mechanisms
• Regulatory mechanisms contain 4
components:
• 1. ______________
• A variable that is controlled by a regulatory
mechanism; for example, temperature in a heating
system.
• 2. ___________
• The optimal value of the system variable in a
regulatory mechanism.
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• Physiological Regulatory Mechanisms
• 3. ______________
• In a regulatory process, a mechanism that signals
when the system variable deviates from its set point.
• 4. ___________________
• In a regulatory process, the mechanism that is
capable of changing the value of the system variable.
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• Physiological Regulatory Mechanisms
• _____________feedback – an essential characteristic of
all regulatory mechanisms
• A process whereby the effect produced by an action
serves to diminish or terminate that action.
• _________________
• A brain mechanism that causes cessation of hunger or
thirst, produced by adequate and available supplies of
nutrients or water.
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Correctional mechanism – in a regulatory process, the
mechanism capable of ___________________ of the system
variable (fluid volume).
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• Drinking
• Some facts about fluid balance
• 4 fluid compartments
• 1. Intracellular fluid
• The fluid contained within cells. (___%)
• Extracellular fluid
• All body fluids outside cells: interstitial fluid, blood
plasma, and cerebrospinal fluid.
• 2. Intravascular fluid
• The fluid found within blood vessels. (__%)
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• Drinking
• Some facts about fluid balance
• 3. Interstitial fluid
• The fluid that bathes the cells, filling the space
between the cells of the body (interstices). (__%)
• 4. Cerebral spinal fluid (1%)
• Isotonic
• Equal in ______________________ to the contents of
a cell. A cell placed in an isotonic solution neither
__________________________.
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Relative size of fluid
compartments.
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• Drinking
• Some facts about fluid balance
• Hypertonic
(may endanger cells)
• The characteristic of a solution that contains enough
solute that it will _________________of a cell placed
in it, through the process of osmosis.
• Hypotonic
(may endanger cells)
• The characteristic of a solution that contains so little
solute that a cell placed in it will ________ water,
through
the process of osmosis.
• _________________
• Reduction in the volume of the intravascular fluid.
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Movement of water molecules.
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• Drinking
• Two types of thirst:
• The body needs two sets of receptors, one for blood
volume, and one for cell volume.
• 1. __________________ thirst
• Thirst produced by an increase in the osmotic
pressure of the interstitial fluid relative to the
intracellular fluid, thus producing ________________.
• Osmoreceptor
• A neuron that detects changes in the solute
concentration of the interstitial fluid that surrounds it.
If this volume is too low – ________________.
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The detectors in the ___________________________ respond
to changes in the interstitial fluids that surround them.
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MRI of brain stimulation from osmotic thirst.
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• Drinking
• Two types of thirst
• Volumetric Thirst
• Thirst caused by hypovolemia; occurs when the
___________________________________.
• Loss of blood causes volumetric thirst. In this case
there is a loss of (1) salt as well as (2) water. The
loss of salt produces a salt appetite.
• Two sets of receptors accomplish this dual function:
Set 1 is located in the kidneys (angiotensinogen).
Set 2 is located in the heart (atrial baroreceptors).
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• Drinking
• Two types of thirst: (1) When the flow of blood to the
kidneys decreases, the detector cells secrete an enzyme
called renin.
• Renin
• An enzyme secreted by the kidneys that causes the
conversion of a protein (angiotensinogen) in the blood
into a hormone called angiotensin.
• Role of angiotensin
This hormone causes _______________________
(increasing blood pressure), it causes the kidneys to
conserve water and sodium, and it initiates drinking
and a ______________.
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Detection of hypovolema.
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• Neural Mechanisms of Thirst
• Subfornical organ (SFO) – the receptor site the initiates
drinking.
• A small organ located in the confluence of the lateral
ventricles, attached to the underside of the fornix;
contains neurons that detect the presence of
angiotensin in the blood and excite neural circuits that
____________________.
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• Neural Mechanisms of Thirst
• Receptor neurons in the SFO send their axons to
the median preoptic nucleus.
• Median preoptic nucleus
• A small nucleus situated around the decussation of
the anterior commissure; plays a role in thirst
stimulated by angiotensin. Stimulation initiates
______________.
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The subfornical organ and
its connection to the median
preoptic nucleus.
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• Atrial Baroreceptors:
the second set of receptors for
volumetric thirst.
• When the blood volume falls, the atria of the heart becomes
less full, and stretch receptors located in the atria detect this
change. The decrement in blood volume is sent to the brain,
and drinking behavior is stimulated in about 30 minutes
(dogs).
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• Eating and Fasting
• The control of eating is more complicated than the control of
drinking and sodium intake.
• To stay alive all cells in the body must have a constant
supply of fuel and oxygen.
• Metabolism has two phases:
• Absorptive phase occurs when ______________ in the
digestive tract.
• Fasting phase occurs when the digestive tract is ______.
• Fuel reservoirs are necessary to keep the cells nourished
when the gut is empty.
The short-term reservoir stores _______________.
The long-term reservoir stores_____.
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• Liver, Insulin & Glycagen: (Short-term _____ calory
capacity). The liver soaks up excess glucose and
stores it as glycogen, and releases glucose from its
reservoir when the digestive tract is empty.
• When glucose and insulin are present in the blood, some of
the glucose is __________________________________.
• Cells in the liver convert glucose into glycogen, and
glycogen is stored in the liver. Insulin, a pancreatic hormone
regulates this process.
• When blood glucose begins to drop, the pancreas responds
by stopping the _________________________________
• _______________________________________________.
• The effect of glucagon is the reverse of that of insulin. It
stimulates the conversion of glycogen into glucose.
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• When the short-term glucose resevoir becomes empty
the body taps into the long-term reservoir (adipose
tissue).
• Adipose tissue is filled with fats (triglycerides).
• Stimulation by the sympathetic branch of the ANS innervate
adipose tissue, the pancreas and the adrenal medulla..
• ANS stimulation causes the triglycrides to be broken down
by glucagon and catecholamines into glycerol, & fatty acids.
• Fatty acids can be metabolized by all the cells in the body
__________________.
• The brain can only metabolize __________. The liver
takes up the _________________________________.
• The brain can absorb glucose in the absence of _______.
All the other cells in the body require insulin to absorb
glucose.
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• Eating: Some Facts about Metabolism
• ____________
• A polysaccharide often referred to as ____________;
stored in liver and muscle; constitutes the short-term
store of nutrients.
• Insulin
• A pancreatic hormone that facilitates entry of glucose
and amino acids into the cell, conversion of glucose
into glycogen, and transport of fats into adipose
tissue.
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• Eating: Some Facts about Metabolism
• Glucagon
• A pancreatic hormone that promotes the conversion of
liver ________________.
• Triglyceride
• The form of fat storage in adipose cells; consists of a
molecule of glycerol joined with three fatty acids.
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• Eating: Some Facts about Metabolism
• _______________
• A substance derived from the breakdown of
triglycerides, along with fatty acids; can be converted
by the_________________.
• Fatty acid
• A substance derived from the breakdown of
triglycerides, along with glycerol; can be metabolized
by most cells of the body except for the brain.
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• Eating: Some Facts about Metabolism
• 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
_________________________________________.
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• Eating: Some Facts about Metabolism
• Absorptive phase
• The phase of metabolism during which nutrients are
absorbed from the digestive system; ____________
• __________________________________________
__________________________________________
__________________________________________
__________________________________________
__________________________________________.
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Absorptive & fasting phase.
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• What Starts a Meal?
• One mechanism is needed to start feeding when
the fuel reservoir is being depleted, and a second
mechanism is needed to stop ingestion when we
eat more calories than needed.
• Signals from the environment
• An empty stomach is an important signal to eat.
• However, many environmental factors motivate us to
eat including:
Sight of food
Smell of food
Behaviors related to food preparation
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• What Starts a Meal?
• Signals from the stomach
• ______________
• A peptide hormone released by the stomach that
increases eating, also produced by neurons in the
brain.
• Duodenum
• The first portion of the small intestines, attached
directly to the stomach. The ghrelin receptors are in
the duodenum.
• The secretion of ghrelin is suppressed when ghrelin
receptors detect the presence of food in the
duodenum. This system is not sensitive to
_________________________.
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Ghrelin levels & the onset of feeding.
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• What Starts a Meal?
• Metabolic signals
• ________________
• A dramatic fall in the level of glucose available to cells;
can be caused by a fall in the blood level of glucose or
by drugs that inhibit glucose metabolism.
• ___________________
• A dramatic fall in the level of fatty acids available to
cells; usually caused by drugs that inhibit fatty acid
metabolism.
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• What detectors monitor the level of metabolic fuels?
• There are two sets of detectors:
• 1. Located in the __________
• 2. Located in the___________
• The liver receives blood from the intestines via the hepatic
portal vein. Receptors in the liver are sensitive to
glucoprivation, and lipoprivation. The vagus nerve sends
this signal to the brain.
• Receptors in the _________ also detect glucoprivation.
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• What Starts a Meal?
• Metabolic signals
• Methyl palmoxirate (MP)
• A drug that inhibits fatty acid metabolism and
produces lipoprivic hunger.
• Mercaptoacetate (MA)
• A drug that inhibits fatty acid metabolism and
produces lipoprivic hunger.
• Hepatic portal vein
• The vein that transports blood from the digestive
system to the liver.
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Blood flow to the liver
via the hepatic portal
vein exposes receptors
in the liver to changes in
lipid and glucose levels.
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• What Stops a Meal?
• Short-term regulation of the sense of satiety.
• 1. Liver sends satiety signals to the brain via the vagus
nerve.
• 2. Insulin receptors in the brain serve to indicate that the
body is in the ________________of carbohydrate ingestion.
• 3. Cholecystokinin
• A hormone secreted by the duodenum that regulates
gastric motility and causes the gallbladder (cholecyst)
to contract; appears to provide a satiety signal
transmitted to the brain through the vagus nerve.
Receptors are between the stomach & duodenum.
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• Long-Term Satiety: Signals from Adipose Tissue
• __ mouse
• A strain of mice whose obesity and low metabolic
rate is caused by a mutation that prevents the
production of leptin.
• Leptin
• A hormone secreted by ______________; decreases
food intake and increases metabolic rate, primarily
by inhibiting NPY-secreting neurons in the arcuate
nucleus.
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Untreated ob mouse
ob mouse treated with leptin
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• Brain Mechanisms
• Brain Stem
• Decerebration
• A surgical procedure that severs the brain stem,
disconnecting the _________________________.
• The only behaviors that a decerebrate animal can
display are those that are directly controlled by neural
circuits located within the ______________________.
• Animal studies indicate that the brain stem contains
neural circuits that can control at least some aspects
of food intake.
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• Brain Mechanisms
• Hypothalamus : Role in hunger
• Lesions of ___________hypothalamus produce cessation of
eating and drinking.
• Lesions of _____________hypothalamus produce gross
obesity.
• Melanin-concentrating hormone (MCH)
• A peptide neurotransmitter found in a system of
lateral hypothalamic neurons that stimulate appetite
and reduce metabolic rate.
• Orexin (AKA hypocretin involved in sleep regulation)
• A peptide neurotransmitter found in a system of lateral
hypothalamic neurons that stimulate appetite and
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reduce metabolic rate.47
Hypothalamic Centers
Ventromedial hypothalamus (VMH) depresses
hunger (stimulation). Destroy it and the animal
eats excessively.
Richard Howard
Revision 2006 PSB
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Feeding circuit
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• Brain Mechanisms
• Hypothalamus : Role in hunger
• Neuropeptide Y (NPY)
• A peptide neurotransmitter found in a system of
neurons of the arcuate nucleus that:
______________feeding
Stimulates insulin and glucocorticoid secretion
Stimulates the breakdown of triglycerides
Decreases body _______________
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• Brain Mechanisms
• Hypothalamus : Role in hunger
• _____________ nucleus
• A nucleus in the base of the hypothalamus that
controls secretions of the _____________ pituitary
gland; contains NPY-secreting neurons involved in
feeding and control of metabolism.
• ________________ nucleus
• A nucleus of the hypothalamus located adjacent to the
dorsal third ventricle; contains neurons involved in
control of the autonomic nervous system and the
_____________ pituitary gland.
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Hunger signal pathway to
the lateral hypothalamus.
Infusion of NPY to the
arcuate nucleus induces
______________.
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• Brain Mechanisms
• Hypothalamus: Role in hunger
• NPY neurons in hypothalamus release AGRP at their
terminals. This peptide induces eating for intervals up to 6
days in duration.
• Agouti-related peptide (AGRP)
• A potent and extremely long-lasting orexigen; A
neuropeptide that acts as an antagonist at MC-4
receptors and increases eating.
• THC may stimulate the AGRP pathway. Used to
stimulate ________________________.
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Satiety signal pathway.
Leptin receptors induce an
inhibitory effect on feeding, &
prevent a decrease in
metabolic rate. The satiety
signal from adipose tissue
________________ the brain
to ________________.
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• Brain Mechanisms
• Hypothalamus: Role in satiety
• CART (arcuate nucleus)
• Cocaine and amphetamine-regulated transcript; a
peptide neurotransmitter found in a system of neurons
of the arcuate nucleus that inhibits feeding.
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Set-Point Theory
Manipulating lateral and ventromedial
hypothalamus and alters the body’s “weight
thermostat.”
If weight is lost – food intake increases and energy
expenditure decreases. If weight is gained – the
opposite takes place.
Revision 2006 PSB
Hunger
• Under feeding – malnourishment
• Over feeding – obesity
• If you eat just one extra carrot a day (20 calories), you will
gain 2 pounds a year, 20 pounds a decade. Thus the
regulation of food intake must to very precise to defend a set
body weight.
Revision 2006 PSB
• Eating Disorders
• Obesity
• Obesity is a widespread problem that can have
serious medical consequences.
• In the United States, 67% of males and 62% of
females overweight (exceed a body mass index of
25).
• Known health hazards of obesity include
__________________________________________
_________________________________________.
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11.21
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2008 Data
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Change in Obesity Rates
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Hunger and Eating
• Identical twins are
•
Body Weights of Twins
more similar in body
weight than are
fraternal twins.
Genetic factors play
a large role in body
weight.
Revision 2006 PSB
Stress, food cues and appetite
• Stress:
•
____________body weight individuals lose
appetite with increases in stress while __________
individuals show the reverse pattern.
____________________________: overweight
individuals feel hungrier to food-related cues than do
average weight individuals.
Revision 2006 PSB
Can you “catch” obesity?
• There is a lot of good advice to help us avoid
becoming fat, such as eat less and exercise. But if
some researchers are right, you may soon be
hearing a surprising new piece of advice:
_________________.
Revision 2006 PSB
Catching Obesity
• There is growing evidence that some viruses may
•
cause obesity, thus making obesity contagious, said
Leah Whigham of the University of Wisconsin,
Madison, lead researcher in a new study on the
subject.
Her study found that a ______________________
AD-37 causes _____________.
Revision 2006 PSB
• Eating Disorders
• Obesity
• People with sedentary occupations eat slightly less than
active people (2400 kcal/day), but burn only about 300 k
cal in physical activity.
• If calories in exceed calories out, then obesity is the
result.
• Uncoupling protein (UCP)
• A mitochondrial protein that facilitates the conversion
of nutrients into heat. It strongly influences metabolic
efficiency.
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• Eating Disorders
• Anorexia Nervosa and Bulimia Nervosa
• ____________________
• A disorder that most frequently afflicts young women;
exaggerated concern with being overweight that
leads to excessive dieting and often compulsive
exercising; can lead to starvation.
• _____________________
• Bouts of excessive hunger and eating; often followed
by forced vomiting or purging with laxatives;
sometimes seen in people with anorexia nervosa.
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