Chapter 52. Hunger and Weight Control

hypothalamus

brain structure involved with motivation; monitors hunger and satiety signals to regulate our experienced hunger drive

incentive

perceived value of a stimulus that pulls us toward a particular type of behavior to obtain that stimulus

incentive value of food

attractiveness of the particular type of food that is available; based on our prior experiences

insulin

hormone released by the pancreas to regulate the level of glucose in the blood

leptin

hormone released by fat cells when they are full of fat; decreases hunger

pancreas

tube-shaped endocrine gland located near the stomach; releases insulin into the bloodstream

satiety

pleasant feeling of being full or having eaten enough

basal metabolic rate

amount of energy expended when the body is in a resting state

drive

a state of tension or motivational force that pushes us toward a particular type of behavior that will reduce the tension

ghrelin

hormone released by an empty stomach; increases hunger

glucose

type of sugar found in blood; main fuel burned by muscles and brain cells; low level of glucose triggers hunger

homeostasis

the body’s tendency to regulate its physiological systems so that each component stays within an optimal range

hormones

chemical messengers of the endocrine system; travel to their target through the bloodstream

hunger

unpleasant feeling of craving food; motivational drive that pushes us toward finding food and eating it

Hunger and Weight Control

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Learning Objectives:

Identify the major physiological and psychological factors that influence hunger.

Explain why it is so difficult for obese individuals to lose weight.

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The figure is a side image of the brain. The hypothalamus in the center of the brain, below the cerebral cortex, is labeled. Psychological signals and physiological signals are shown entering the hypothalamus.

1. Hunger is a drive that is important for our survival because it motivates us to search for and consume the food that our body needs for energy and tissue repair. The signals that influence hunger converge on a brain structure called the hypothalamus, which generates the urges that make us want to eat, or the feeling of satiety that makes us stop eating.

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The figure represents a scale. When the scale is balanced there is homeostasis and a normal glucose level. When the scale is unbalanced due to glucose being too high, the pancreas releases more insulin. This causes the body's cells to use and store more glucose. This results in a decrease in hunger and less food consumed. Homeostasis returns as glucose level returns to normal. When the scale is unbalanced due to glucose being too low, the pancreas releases less insulin. This causes the fat cells to release stored glucose into the blood stream. This results in an increase in hunger and more food consumed. Homeostasis returns as glucose level returns to normal.

2. Some of the physiological signals for hunger arise from homeostasis, the process of maintaining body chemistry within an optimal range. For example, when the level of glucose in the blood changes, the pancreas adjusts its release of insulin to keep glucose from getting too high or low. The hypothalamus monitors the level of glucose and insulin, and triggers hunger when glucose falls.

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3. Other physiological signals arrive at the hypothalamus from receptors that measure the level of fullness or the contents of the stomach, intestines, and fat cells. An empty stomach secretes the hormone ghrelin, which increases hunger. Fat cells stuffed with fat secrete the hormone leptin, a satiety signal that decreases hunger.

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4. In addition to the physiological signals, the hypothalamus also receives psychological signals based on our past experiences with food. When we see or smell food that we have learned is delicious, that food serves as an incentive, pulling us in the direction of eating. We will be motivated to eat that food even if our body doesn’t need more fuel at that moment.

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5. Cues from the social environment also influence hunger. We typically get hungry when the clock indicates our normal mealtime, even if we have just been snacking. Food also seems to taste better (has higher incentive value) when we are in the company of family or friends.

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The image is a bar graph. The X axis is labeled Weeks of dieting ranging from 1 to 8 in incremements of 1. The Y Axis is labeled Basal metabolic rate (calories burned per hour while sleeping) ranging from 50 to 90 in increments of 10. The approximate data for the graph is presented in the following table. The data represents a steady decline in basal metabolic rate over time as the weeks of dieting increase. The table for graph consists of two columns Weeks of dieting, Basal metabolic rate. The first row in the first column 1, in the second column 87, the second row contains 2 and 80, the third row contains 3 and 73, the fourth row contain 4 and 67, the fifth row contains 5 and 65, the sixth row contains 6 and 65, the seventh row contains 7 and 65, the eighth row contains 8 and 63.

6. When people try to lose weight by consuming less food, all of these hunger signals are working against them. The hypothalamus mistakenly assumes the body is starving, and then raises the hunger drive to a higher level. In addition, the hypothalamus lowers the body’s basal metabolic rate so that daily activities burn fewer calories.

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Practice: Exploring Hunger Signals

Roll over each of the labels to review the various signals that influence our experience of hunger.

Hypothalamus

Incentive value of food

Glucose and insulin

Ghrelin

Leptin

Description:

Hypothalamus: monitors the levels of all relevant hormones and other substances in blood, and regulates the level of experienced hunger

Incentive value of food: based on learned preferences; food that looks or smells delicious is a signal for the hypothalamus to increase hunger

Social setting: based on past experiences; mealtime with family or friends is a signal for the hypothalamus to increase hunger

Glucose and insulin: regulated by pancreas; high level of blood glucose triggers release of insulin, which lowers the level of blood glucose, signaling the hypothalamus to increase hunger

Ghrelin: released by an empty stomach; high level of the hormone ghrelin is a signal for the hypothalamus to increase hunger

Leptin: released by full fat cells; high level of the hormone leptin is a signal for the hypothalamus to decrease hunger

The figure is a side image of the brain. Physiological signals is listed at the top of the left side of the screen. Under physiological signals is glucose and insulin, ghrelin, and leptin. Psychological signals is listed at he top of the right side of the screen. Under psychological signals is incentive value of food and social setting. The hypothalamus is listed in the center of the image below the brain.

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Quiz 1

Match the terms to their descriptions by dragging each colored circle to the appropriate gray circle. When all the circles have been been placed, select the CHECK ANSWER button.

Select the NEXT button and move to Quiz 2.

Perhaps you should go back to review the physiological and psychological factors that influence hunger.

drive

ghrelin

glucose

homeostasis

incentive

insulin

leptin

satiety

hormone released by an empty stomach; increases hunger

perceived value of a stimulus that pulls us toward a particular behavior

aroused motivational force that pushes us toward a particular behavior

type of sugar found in blood; main fuel burned by muscles and brain cells

a state of internal balance that keeps body functions within an optimal range

hormone released by the pancreas to regulate the level of glucose in the blood

hormone released by fat cells when they are full of fat; decreases hunger

pleasant feeling of being full or having eaten enough

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Select the NEXT button and move to the Conclusion.

Try to respond to the statements again.

Quiz 2

For each of the statements, select one of the options to indicate whether the event described would lead to an Increase or Decrease in your experience of hunger. When responses are chosen for all statements, select the CHECK ANSWER button.

Increase	Decrease
		Your blood glucose level is falling rapidly.
		Your body’s fat cells are releasing leptin.
		The clock points to your normal lunch time.
		Your stomach is increasing its secretion of ghrelin.

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Congratulations!

You have completed the activity Hunger and Weight Control.