Control of food intake

Question 1

How do we control food intake?

Answer 1

Hunger

desire/need for food

Appetite

feeling of eating certain foods

Satiation

Feeling full after meal

Satiety

Feeling full and not eating any more meals

Question 2

What part of the body controls food intake?

Answer 2

The brain = Hypothalamus

Question 3

What is arcuate nucleus?

Answer 3

ARC have a role in integrating appetite signals

• within the hypothalamus
• not covered by BBB; gut hormones can pass into brain

Question 4

What is POMC?

Answer 4

Modifies to generate melanocortin peptides

• act at melanocortin receptors
• MC4R = mutation leads to hyperphagia (lose control of appetite = constant hunger) which then leads to severe obesity
• AgRP is an antagonist of the melanocortin-4 receptor = stimulate hunger

Question 5

Gastric distension leads to a release of a number of hormones from the _____ cells.

Name ALL hormones

How does all the hormones affect food intake?

Answer 5

Gastric distension leads to a release of a number of hormones from the enteroendocrine cells

cholecystokinin (CCK)

glucagon-like peptide-1 (GLP-1)

Oxyntomodulin

peptide YY

apolipoprotein A-IV

enterostatin

They all inhibit food intake

Question 6

What is Leptin?

How does it inhibit food intake?

Answer 6

Peptide hormone released from adipose tissue

Inhibits food intake by reducing leptin levels

Reversed by refeeding/insulin

Production of leptin correlates w/ amount of adipose tissue

Mutations causing absence of leptin leading to severe obesity

Leptin is transported into the brain + inhibits NPY AgRP release

• Activates POMC/CART neurons
• Switch from appetite stimulation to appetite suppression

Question 7

How does Insulin inhibit food intake?

Answer 7

Crosses BBB through receptor-mediated process

Decreases intake + body weight by acting on ARC

Insulin resistance leads to loss of apetite control

Question 8

When is Ghrelin secreted?

Answer 8

Secreted when anticipating food

Acts on ARC to stimulate food intake through NPY + AgRP

• Produced from GIT*
• Hunger at certain times of the day is due to ghrelin*

Ghrelin levels peak before meal + stimulate hunger

If obese but trying to lose weight, ghrelin levels increase

Ghrelin antagonist in development to cause weight loss

Question 9

Discuss PYY

Answer 9

Secreted from GIT

Dependent on certains food (more from protein)

Stimulated by CCK, gastric acid + bile

PYY _1-36 cleaved to PYY _3-36 at NPYY_{<strong>2</strong>} receptor

Inhibits food intake (via vagal inputs)

PYY levels stay elevated for 12 hours post meal

Question 10

How does CCK inhibit food intake?

Answer 10

Released from duodenum + jejunum in response to fatty acids

Act on vagal nerves

Cross BBB and act on hypothalamus

Question 11

Discuss reward centres + how it links to appetite

How does dopamine + cannabinoid affect reward processes?

What is bupropion?

Answer 11

Appetite linked to reward processes in the brain

Examples include:

• opioid receptors
• cannabinoid receptors
• dopamine receptors

As you eat food, more dopamine is released

Degree of pleasure correlates with the amount of dopamine rleased

Bupropion - dopamine reuptake inhibitor = weight loss

Food reward also depends upon CB1 receptor activation

• can regulate dopaminergic system
• Rimonabant - B1 receptor antagonist