1 chapter 9 motivation. 2 internal regulatory systems usually work, but… the percentage of obese...
TRANSCRIPT
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Chapter 9
Motivation
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Internal Regulatory Systems Usually Work, But…
The percentage of obese Americans jumped from 12% in 1991 to 21% in 2001.
At the same time, 1–3% of Americans are diagnosed with anorexia nervosa or bulimia nervosa.
© Annebicque Bernard/CORBIS SYGMA
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Cultural Factors Can Override Biological Systems
Prior to the introduction of American television programs in 1996, a “robust, well-muscled body” represented the Fijian ideal.
Anne Becker reports that dieting and eating disorders are now increasing among young women in Fiji.
© Craig Lovell/CORBIS
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Why do we eat?
Repair & maintain body “building blocks”
Get energy Movement Warmth
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Absorption of Nutrients
Carbohydrates are broken down into simpler sugars (ex. glucose).
Proteins are broken down into amino acids.
Fats are broken down into fatty acids.
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Immediately used Glucose (needs insulin to get into
cells)
Fatty acids
Amino acids
Metabolism
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Creating Energy Stores Short-term
Carbohydrates broken down into glucose Insulin from the pancreas turns glucose into
glycogen Stores glycogen in the liver & muscles
Long-term Fatty acids/amino acids turned into fats
(triglycerides) Stored in adipose tissue (fat cells)
Metabolism
8Copyright © 2004 Allyn and Bacon
Metabolism
acids
Insulin
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Diabetes Mellitus
Failure to move glucose out of blood supply due to insulin dysfunctions.
Type I: results from destruction of insulin-producing
cells. Type II:
obesity leads to insulin resistance.
Symptoms include extreme thirst, frequent urination, fatigue and weight loss
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Using Energy Stores (i.e., not using glucose already floating around in blood stream from eating) Fasting phase:
Glucagon:
Triglyceride:
Metabolism
Copyright © 2004 Allyn and Bacon
Metabolism
acids
Insulin
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What Starts a Meal? Hunger Cues
External cues Sight and smell of delicious food Time of day Other habits (e.g. must eat while watching TV)
Internal cues Stomach growling Lack of glucose availability to cells
(glucoprivation) Low quantities of stored fats (lipoprivation)
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Detectors Liver:
Receptors in liver detect glucose and fatty acid deficiency, influence how much insulin and glucagon the pancreas releases
Brain: Glucoreceptors in the hindbrain for
glucose send a signal to the lateral hypothalamus through the vagus nerve
What Monitors Food Intake?
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The signals that stop a meal (satiety signals) are different from the signals that start a meal
Satiety Signals Short-term (during act of eating)
Long-term (from adipose tissue)
What Stops a Meal?
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Short-term satiety Head factors
Taste and odor of food Act of swallowing Appearance of food
Gastric factors Receptors in stomach (detect
nutrients) Fullness
What Stops a Meal?
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Short-term satiety Intestinal Factors
Duodenum: Receptors for glucose and fatty acids Cholecystokinen (CCK):
A hormone secreted by the duodenum Prompts gallbladder (cholecyst) to contract
and produce bile Provides a satiety signal sent to brain
What Stops a Meal?
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Short-term satiety Brain areas (Ventral medial
hypothalamus) Lesions of the VMH produce
weight gains.
excess insulin production.
But VMH lesions may disrupt pathways linking other hypothalamic nuclei.
What Stops a Meal?
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Long-term satiety Adipose Tissue
Leptin: A hormone secreted by adipose tissue Decreases food intake
Increases metabolic rate
Ob mouse (obese): A strain of mouse whose obesity and low
metabolic rate is caused by a mutation that prevents the production of leptin.
What Stops a Meal?
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20Copyright © 2004 Allyn and Bacon
Physiological Regulatory Mechanisms
Thermostat Metaphor