1

Chapter 9

Motivation

2

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

3

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

4

Why do we eat?

Repair & maintain body “building blocks”

Get energy Movement Warmth

5

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.

6

Immediately used Glucose (needs insulin to get into

cells)

Fatty acids

Amino acids

Metabolism

7

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

9

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

10

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

12

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)

13

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?

14

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?

15

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?

16

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?

17

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?

18

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?

19

20Copyright © 2004 Allyn and Bacon

Physiological Regulatory Mechanisms

Thermostat Metaphor