PSYC1017 Ingestion

Metabolism

All chemical reactions in the body

Respiration

The breakdown of glucose making energy available to the organism

Insulin

A hormone used in conversion of glucose to glycogen

Glucagon

A hormone used in conversion of glycogen to glucose

Cephalic Phase

Expectation of food
Increases insulin, decreases glucagon

Absorptive Phase

Meeting energy requirements by eating
Increases insulin, decreases glucagon

Fasting Phase

Energy withdrawn from energy stores
Decreases insulin, increases glucagon

Campfield & Smith (1990)

Drop in blood glucose levels starts a meal

Le Mangen (1981)

BG levels don't normally vary even under long periods of fasting
Diabetics get hungry even though they have high BG levels

Ghrelin

Peptide hormone released by the stomach to induce hunger

Cummings (2006)

Ghrelin levels increase in the blood before each meal

Schmid (2005)

Intravenous injections of Ghrelin enhanced appetite and elicited vivd images of the participants' favourite foods

Schaller (2003)

The release of Ghrelin is controlled by the contents of the stomach, not the availability of nutrients in the blood.

External Factors of Hunger

Smell of food
Adverts
Time of day
Places where you eat

Weingarten (1983)

Paired a buzzer with food and a bell with innter-meal times.
Dogs would press lever for food when they heard a buzzer, but not the bell

Birch (1989)

Children can also learn complex connections during classical conditioning

Wilson (1990)

Force feeding increases weight and decreases voluntary eating

Kahler (1998)

Leptin injections in normal mice stops hunger

Cannon & Washburn (1912)

Eating balloons imitates feeling full
Vagus nerve records stretching of stomach lining

Greenberg (1990)

Entry of food into the intestines inhibits feeding

Gibbs (1973)

Injections of cholecystokinin suppress feeding

Pederson-Bjerdgaard (1996)

Peptide YY released by stomach after meal in proportion to calories eaten

Batterham (2007)

Injection of Peptide YY inhibits the size of meals

Weingarten & Kulikovsky (1989)

Learning is an external factor that stops hunger

Rolls (1981)

Previous experience of foods is an external factor that stops hunger

Berry (1985) Polivy (1979)

Social factors are external factors that stop hunger

Arcuate Nucleus

A collection of neurons in the Mediobasal hypothalamus that repond to Ghrelin

Van den Top (2004)

The arcuate nucleus secretes neuropeptide Y as a response to Ghrelin

Anand & Brobeck (1951)

The lateral hypothalamus is a feeding centre
Electrical stimulation causes hunger
Lesions cause lack of hunger

What is the Lateral Hypothalamus is stimulated by the Arcuate Nucleus?

Neuropeptide Y stimulates activity of MCH and Orexin, which stimulate hunger and decrease metabolic rate

How does the Arcuate Nucleus stop hunger?

Leptin inhibits the release of NPY
The arcuate nucleus releases anorexigens that suppress appetite
Leptin activates anorexigens, which inhibit MCH & Orexin

Ravussin (1994)

Populations of similar genetic backgrounds but located in US & Mexico with different jobs & diets show different incidence of obesity

Levin, Eberhardt & Jensen (1999)

Overweight people are sedentary for 2.5 hours more than lean people

Bray, Neilsen & Popkin (2004)

Snack foods contain high-fructose corn syrup
Fructose doesn't stimulate insulin or leptin production

Sims & Horton (1968)

Same diet and life style in prisoners only caused obesity in some prisoners

Bouchard (1990)

Twins put on in weight in the same places

Price & Gottesman (1991)

Obesity is 85% due to heredity

Strunkard (1986)

Children of obese parents are more likely to be obese, even if their adoptive parents aren't obese

Licinio (2004)

Some people have a leptin deficiency

Schwartz (1996)

High leptin levels in people can lead to insensitivity

Caro (1996)

No leptin in cerebrospinal fluid

Finer (2014)

Influence of early experience on leptin sensitivity

Rose & Williams (1961)

Some people have more glucose left over after efficient metabolism

Levine, Eberhardt & Jensen (1999)

The amount of fat tissue that a person gained was inversely related to their level of non-exercise activity thermogenesis

Scarpace (2000)

Uncoupling protein (UCP) plays an important role in metabolism efficiency

Schrauwen (1999)

Increasing UCP levels linked with increasing metabolic rate, so less glucose left over

Dittman (2024)

Labradors have a genetic mutation for more efficient metabolism (more leftover glucose)