Motivation: Feeding - 15

Question 1

What are some obesity trends?

Answer 1

At least 60% of adults in the UK are overweight, 20% are considered obese. Over 30,000 death a year are caused by obesity in England alone. Disruption of biological control systems is thought to be a major factor. Social & culture factors play a major role in development of eating disorders.

Question 2

What are 3 life threatening eating disorders?

Answer 2

1. Anorexia nervosa - a syndrome in which individuals severely deprive themselves of food.
2. Bulimia - marked by periodic gorging and purging by vomiting or laxatives
3. Binge eating - gorging with more food than is necessary to satisfy hunger.

Question 3

How does the body use energy?

Answer 3

The body uses energy in 3 primary ways:

1. Basal Metabolism: 55% of energy usage is to maintain body heat and other resting function
2. Digestion of food: 33% of energy is used to process food and break it down into molecules to be used by the body
3. Active Behavioural processes: 12-13% of energy usage is for behaviours other than rest - varies greatly depending on activity level.

Remaining energy is typically stored as energy reserves.

Question 4

What are sources of energy?

Answer 4

1. Carbohydrates (Saccharides): 4kcal per gram, carbs get converted to glucose and provide principle source of energy. Storable form of carbohydrates are called glycogens - stored in live and muscles - short term storage (non-essentials)
2. Amino Acids (Protein): 4 kcal per gram. Comes from proteins, basic building blocks for all cells. 20 amino acids, 9 cannot be produced by the body = essential amino acids. Amino acids can be converted to glucose.
3. Lipids (Fats): 9kcal per gram. Long term energy storage. Fats can be converted to free fatty acids as alternate energy source (essential).
4. Vitamins and Minerals: needed to assist in bodily functions (digestion, cell building, homeostasis, etc.) (essential)

Question 5

What is homeostasis and drive reduction?

Answer 5

Maintaining a stable internal state.

1. Set-point - physiological parameter
2. Error detector - compares actual versus set-point state
3. Error correction mechanism - negative feedback mechanism

Motivational (feeding) drive emerges from need to avoid deviations from the narrow set-point.

Question 6

How does feeding maintain homeostasis?

Answer 6

Traditional ideas saw absolute blood glucose as likely signal for hunger: glucose is the main source of energy, lack of glucose would represent nutrient deficit. Two basic types of set-point are thought to regulate food intake:

1. Glucostatic Set-Point Theory: eating is controlled by deviations from a hypothetical blood glucose set-point (Glucostat receptors)
2. Lipostatic Theory: Eating is controlled by a hypothetical body-fat set-point (long-term homeostatic maintenance)

Question 7

What is the dual-centre hypothesis?

Answer 7

VMH lesions increase feeding and weight (satiety centre). LH lesions decrease feeding and weight (hunger centre). Damage to lateral hypothalamus (LH) causes a large decrease in feeding (aphagia) and reduced body size - hunger centre. Damage to the ventromedial hypothalamus (VMH) has opposite effect by increasing feeding (hyperphagia) - satiety centre.

Question 8

What are problems with the dual centre hypothesis?

Answer 8

LH brain self-stimulation is rewarding in rats. Brain sites where stimulation causes eating are the same sites where self-stimulation is rewarding. LH stimulation sometimes produces feeding, but just as often other behaviours (e.g. drinking, aggression) - effects of LH stimulation depends on the situation.

Question 9

What are peripheral hunger signals?

Answer 9

Ghrelin and orexin - peptide hormones secreted in the gut and from adipos tissue and hypothalamus. Administration of these hormones increase hunger.

Question 10

What are peripheral satiety cues?

Answer 10

Cholecystokinin (CCK) is a hormone released in the intestines in response to fat - CCK injections inhibit subsequent feeding. 
Polypeptide YY (PYY) is also released in the gut in response to food - Injections of PYY inhibit eating. PYY may be abnormally low in obsess individuals. 
Leptin - leptin deficiency associated with obesity. Leptin binds to receptors in the ventromedial nucleus of the hypothalamus.

Question 11

How does appetite work as a motivational system?

Answer 11

Appetite as a negative feedback homeostatic system based competitions between hunger and satiety signals:
Dedicated drive signals indicating the need for nutrients (hunger)
Lateral Hypothalamus
Hormones, e.g., Ghrelin, orexin
2) Dedicated signals relating to food ingestion (satiety)
Ventral Medial Hypothalamus
Hormones, e.g., CCK, PYY, Leptin
But, signals for food (e.g., smells or tastes) often increase feeding even under food sated conditions
Stimulation of appetite through taste and smell
Learned associations – Garcia and Koeling Taste Aversion Experiment