Metabolism - Control of Food Intake:

Question 1

Control of Food Intake

Answer 1

• Human energy intake and body weight are thought to be regulated by homeostatic mechanisms and fluctuate only within narrow limits.
• A challenge to this theory is the current epidemic of obesity. Ready access to plentiful, palatable and affordable food may override any regulatory mechanisms we possess and may explain rising obesity rates
• Some researchers suggest that during millions of years of evolution, humans developed mechanisms that protect us from energy deficits but due to the lack of periods of food abundance in human history, we have not developed mechanisms that protect us from excess food consumption.

Question 2

Regulation of Food Intake: CCK and mechanoreceptors

Answer 2

See diagram in notes.
In the presence of food and drink in the stomach and intestine
In the presence of food and drink in the duodenum
Gastrointestinal Distension activates mechanoreceptors in the stomach
Cholecystokinin (CCK) is released by the duodenum
= Feeling of satiety

Question 3

Regulation of Food Intake: Nutrients

Answer 3

Digestion =
Carbohydrates - Glucose
Fats - Fatty acids
Proteins - Amino acids

All = The liver signals the presence of these nutrients to the brain via the Vagus nerve = satiety

Question 4

Control of Appetite

Answer 4

• The hypothalamus plays a major role in appetite regulation.
• In the arcuate nucleus of the hypothalamus, there are neurons which stimulate or inhibit food intake and influence energy homeostasis.
• Gut hormones act peripherally to modulate digestion and absorption of nutrients and they reach the hypothalamus from the circulation or via the Vagus nerve.
• However, there are other messengers that act as neurotransmitters within the central nervous system to control food intake.

Question 5

Neuroscience of Food Intake

Answer 5

Hormone / Neurotransmitter: Neuropeptide Y (NPY)
Effect on Appetite: Increases
Description: Potent stimulant of food intake.

Hormone / Neurotransmitter: Cholecystokinin (CCK)
Effect on Appetite: Decreases
Description: Producedby the duodenum; promotes satiety.

Hormone / Neurotransmitter: Insulin
Effect on Appetite: Decreases
Description: Potentiates the satiating effect of CCK.

Hormone / Neurotransmitter: Glucagon
Effect on Appetite: Decreases
Description: Major role in glucose metabolism. Decreases appetite.

Hormone / Neurotransmitter: Glucagon-like peptide 1 (GLP-1)
Effect on Appetite: Decreases
Description: Similar in function to Glucagon. Promotes satiety.

Hormone / Neurotransmitter: Bombesin
Effect on Appetite: Decreases
Description: A peptide found in the brain and GI tract; acts in similar fashion to CCK.

Hormone / Neurotransmitter: Ghrelin
Effect on Appetite: Increases
Description: Made by the stomach, increases with food deprivation and may trigger hunger.

Hormone / Neurotransmitter: Leptin
Effect on Appetite: Decreases
Description: Made by fat cells. Promotes satiety and stops feeding behaviour.

Question 6

Cholecystokinin (CCK)

Answer 6

• CCK is secreted in response to the presence of food in the duodenum:
  o It stimulates the gall bladder to release bile.
  o It stimulates the pancreas to release pancreatic juice (digestive enzymes).
  o It delays gastric emptying.
  o It acts on CCK receptors throughout the central nervous system (CNS) and in the satiety centres in the brain stem.
• Meals rich in protein and fat stimulate CCK more than meals that just contain carbohydrates.