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Homeostasis &
Hunger:
Your Body’s Constant
Drive to Stay in
Balance
Homeostasis
• A tendency to maintain a balanced or
constant internal state
• The regulation of any aspect of body
chemistry, such as blood glucose, around
a particular level
• Any change in levels, up or down, results
in being motivated to bring the level back
to normal.
Energy Balance
•Positive energy balance occurs when caloric intake exceeds
calories expended for energy. The excess glucose is converted
to body fat.
•Negative energy balance occurs when caloric intake falls short
of the calories expended for energy. Body fat stores shrink as the
reserve energy in fat cells is used
Basal Metabolic Rate (BMR)
AKA your metabolism!
• The body’s
resting rate of
energy
expenditure
• The rate at which the body
uses energy
for vital functions while at rest
• Factors that influence BMR
• Age
• Gender
• Size
• Genetics
• Food intake
There is a steep decline in the rate at which your body uses energy
for vital functions, such as heartbeat, breathing, and body heat.
Your BMR continues to decrease by about 2 to 3 percent during each
decade of adulthood.
At all points in the lifespan, women’s metabolic rate is 3 to 5 percent
lower than men’s
Body Mass Index:
A measure for
human body
shape based on an
individual’s
weight and
height.
(This equation
doesn’t account
for differences in
muscle vs. fat.)
We’re # 1!
Factors Contributing to Being
Overweight
• Highly palatable food—we eat because it tastes so
good
• SuperSize It—food portions are larger than
necessary for health
• Cafeteria Diet Effect—more food and more variety
leads us to eat more
• Snacking—does not cause us to eat less at dinner
• BMR—changes through the lifespan
• Sedentary lifestyles
Set Point
• A person’s average weight long term
• (NOT necessarily a person’s ideal weight!)
• When the body falls below this weight,
increased hunger and a lower basal
metabolic rate (BMR) may act to restore the
lost weight.
Physiology of Hunger
Hypothalamus – The Control Center
States of the Brain
Cerebral cortex
Hypothalamus
• The hub of
many central
drive systems
lies in the
hypothalamus
Portion of
limbic system
Pituitary
gland
Brainstem
Hunger Drive
• Two areas of the
hypothalamus,
the lateral and
ventromedial
areas, play a
central role in
the hunger drive
Hypothalamus
Hypothalamus
Ventromedial Area
• Decreases Hunger
• Lesions (tissue damage)
alter digestive and
metabolic processes
• Food is converted into fat
rather than energy
molecules, causing animal
to eat much more than
normal
and gain weight
• Lesions = Fat
rats!!
Hypothalamus
Hypothalamus
Lateral Area
• Increases Hunger
• Lesions reduce
hunger drive as
well as general
arousal
• Lesions =
Skinny rats!
Hypothalamus
Hypothalamus
The Appetite Hormones
• Insulin: Hormone secreted by pancreas; controls blood
glucose.
• Leptin: Protein secreted by “bloated” fat cells; when
abundant, sends a message to “stop eating” to brain
that increases metabolism and decreases hunger.
• Orexin: Hunger - triggering hormone secreted by
hypothalamus. As glucose levels drop, orexin levels
increase and person feels hungry
• Ghrelin: Hormone secreted by empty stomach; sends "I'm
hungry" signals to the brain.
• Corticotropin-Releasing Hormone (CRH): hormone in
hypothamalus that sends "I'm not hungry" signals to the
brain.
Eating Disorders
Eating Disorders
• Anorexia nervosa —characterized by
excessive weight loss, irrational fear of
gaining weight and distorted body image
• Bulimia nervosa —characterized by binges
of extreme overeating followed by selfinduced purging such as vomiting, laxatives
• Binge-eating —disorder characterized by
recurring episodes of binge eating without
purging.
• **Body Dysmorphic Disorder
Men’s & Women’s Body Images
According to surveys on body image, people in our society are much
more dissatisfied with their bodies now than they were a generation
ago. Women are still more dissatisfied than men, but today’s men are
more dissatisfied with their bodies than the men of a generation past.
Anorexia Nervosa
Key Features
1. Refusal to maintain a normal
body weight
2. Intensely afraid of being
overweight.
3. Suffer from delusions of being
overweight.
4. Denies there is a problem.
• Usually in adolescent females
• May put themselves on selfstarvation regimens
• May become dangerously
underweight
Bulimia Nervosa
• An eating disorder characterized by
episodes of overeating (usually high
calorie foods)
• Overeating is followed by vomiting, using
laxatives, fasting, or excessive exercise
• Usually stay within their normal weight.
• Usually recognize they have an eating
disorder.
Pica
•
•
•
•
Strange but True!
Hippocrates the first to describe the disorder
People display a compulsive craving for inedible
substances such as clay, dirt, laundry starch,
chalk, buttons, paper, dried paint, burnt
matches, ashes, sand, oyster shells or broken
crockery.
Seen most often in pregnant women or nursing
women but also with people with severe mental
disorders.
Could be a behavioral response to stress.