Control of Food Intake

Question 1

Define:

1. Hunger
2. Appetite
3. Satiety
4. Aphagia
5. Hyperphagia

Answer 1

1. Discomfort caused when the stomach is emptied – Ghrelin is released
2. The psychological desire for food – hunger-stimulated
3. Where you feel full – stomach is distended as VIP/NO is released
4. Inability/refusal to swallow
5. Abnormally great desire for food (↑appetite)

Question 2

What is Vagotomy?

How does this affect stomach accommodation and gastric emptying? What will this cause?

Answer 2

• Cut of vagus nerve

- ↓Stomach accommodation and delays the rate of gastric emptying – causes EARLY SATIETY

Question 3

What mainly controls food intake?

What are the other controls of food intake? What is it affected by?

LOOK AT PICTURE!

Answer 3

• Hypothalamus, which has several nuclei that regulate energy homeostasis:

• Lateral Hypothalamus (LH) - FEEDING CENTRE - lesion in LH = APHAGIA
• Ventromedial Nucleus (VMN) - SATIETY CENTRE - lesion in VMN = ↑appetite (HYPERPHAGIA)
*Both the LH and VMN can restrain feeding if required

• Dorsomedial Nucleus (DMN) – hunger centre – release of NPY into DMN = ↑feeding
• Paraventricular Nucleus (PVN) – modulates feeding behaviour using NPY, GABA, Opioids
• Arcuate Nucleus – neurons produce Orexigenic (↑Appetite) signals
• Prefrontal Cortex and Limbic system control food intake - affected by habit

Question 4

What are the Anorexigenic factors?

Outline the Diurnal variation of food intake

Answer 4

• ↓Appetite e.g. Serotonin, Dopamine, GABA
• Carbs metabolised in the day, fats metabolised in the night - hypothalamus responds to the switch between carb and fat metabolism

Question 5

What mainly controls appetite?

How does temperature affect appetite?

How does the tone of the stomach affect appetite?

How occurs on fat ingestion?

Answer 5

• Plasma glucose – stimulate glucoreceptors in hypothalamus
  • ↓Plasma glucose = ↑Appetite
  • ↑Plasma glucose = ↓Appetite
• ↓Temperature = ↑Appetite
• Distension of full stomach inhibits appetite, contraction of empty stomach
  stimulates appetite
• Fat Ingestion = ↑CCK = ↓Gastric emptying causes the release of Satiety factors

Question 6

What’s the role of Leptin in the control of food intake?

Answer 6

SATIETY HORMONE!!

Is an Anorexigenic substance = ↓Appetite

• White adipose tissue = ↑Leptin = ↓Appetite
Leptin:
• Increases expression of Anorexigenic factors (CRH)
• Stimulates metabolic rate
• Inhibits NPY (Neuropeptide Y) and Ghrelin secretion

*OBESITY CAN LEAD TO LEPTIN RESISTANCE!

Question 7

What’s the role of Ghrelin in the control of food intake?

Answer 7

Is an Orexogenic substance = ↑Appetite

• Fast-acting and stimulates food intake – released by stomach, pancreas, adrenals - secretion is inhibited by Leptin
• ↑Ghrelin before meal, and ↓Ghrelin after meal. It:
o Increases expression of NPY
o Suppresses ability of Leptin to stimulate anorexigenic factors

Question 8

What’s the role of Obestatin in the control of food intake?

Answer 8

• Produced by Epithelial cells of stomach
• Imbalance of it may have a role in obesity
• Encoded by Ghrelin gene but has opposite effects on food intake
o ↓Appetite to ↓body weight gain
o Antagonises effects of Ghrelin and GH secretion

Question 9

What’s the role of Cholecystokinin (CCK)?

Answer 9

• Produced by I-cells of duodenum and CNS neurons. It:
o Inhibits gastric emptying and gastric acid secretion, stimulates release of digestive enzymes from Pancreas – Digestion of fat, protein, carbohydrates
o Increased production of Bile, stimulates contraction of Gallbladder and relaxation of Sphincter of Oddi – fat emulsification

• Mediates satiety by acting on CCK receptors