Control of food intake Flashcards
Describe the volume of the stomach when we have not eaten (fasting)
In an empty stomach, the volume is small.
50ml
What happens to the stomach when we begin to eat food?
The fundic area of the stomach enlarges to accommodate food. NO and Vasoactive intestinal polypeptide allow this to happen.
1.5L
What motion allows the stomach to empty?
We get contraction of the antrum area of the stomach
What hormone stimulates appetite?
Ghrelin
What causes the stomach to relax when we swallow food?
Co-ordinated by:
- Receptive
- Adaptive
- Feedback relaxation
Inhibitory vagal fibres release acetycholine that activate the enteric pathways that release NO, PACAP, VIP and ATP to relax the muscle
In order to relax what do fats and lipids release in order for the stomach to relax to it can receive food?
CCK
What is vagotomy and what does it cause?
A surgical operation in which one or more branches of the vagus nerve are cut, typically to reduce the rate of gastric secretion (e.g. in treating peptic ulcers).
Reduces accommodation and gastric compliance
Define Hunger
Discomfort caused by lack of food and the desire to eat – a strong physiological craving/drive for food/sensation of emptiness in the stomach
Define appetite
Psychological desire/drive to satisfy the body’s needs of food; a hunger-stimulated response
Define satiety
State of being full after eating food (joyous moments – no longer need to continue eating)
Define aphagia
The inability or refusal to swallow
Define Hyperphagia/polyphagia
An abnormal desire for food (extreme unsatisfied drive to eat)
What is food intake controlled by?
It is controlled by the Hypothalamic control
Give 2 reasons for differences in BMI?
Genes (70%)
How much we eat and its composition
Foods are metabolised at different times in the day:
Carbs
Fats
When are they metabolised?
- Carbohydrates metabolised during the day
- Fats metabolised at night
- Hypothalamus responds to the switch between carbohydrate and fat metabolism
What else can appetite be influenced by?
Family gatherings, food palatability, emotional, habitual, and circadian factors
How does the hypothalamus control food intake?
• The base of the hypothalamus has several nuclei that regulate energy homeostasis
→ Control the appetite; size of helping, and our ingestive behaviour
What is the satiety centre in the body?
Hypothalamus (ventromedial nuclei - wall of paraventricular)
What happens when we get stimulation of ventromedial nuclei?
Aphagia
What happens when we get lesions of ventromedial nuclei?
Hyperphagia (an increased appetite or excessive hunger)
Where is the thirst centre located?
Lateral hypothalamus
Do opioids increase appetite
Yes
What does the dorsomedial nucleus control (DMN)?
Modulates energy intake (hunger centre)
What does the release of NPY cause and where does it act?
DMN and increases feeding
What does the Paraventricular nucleus (PVN) do?
Modulates feeding behaviour
NPY, opioids, and GABA all do?
Increase feeding, GABA has mixed effects
What does leptin do? (1)
Decreases food intake
What is the Suprachiasmatic nucleus and what does it control?
- Human body clock is located in the suprachiasmatic nuclei
* Perception of the light-dark cycle (circadian rhythms)? Appetite or the sensation of hunger → mood/drive to eat
What is the amyloid nucleus and what is its role?
• A role for medial amygdaloid nucleus in feeding
• behaviour has been proposed
It is a sub-region of the amygdaloid complex;
Participates in the regulation of food intake
What do Ligands: 5-HT (via 5-HT2C and 5-HT1A) do? (2)
a and fi
Decreases appetite
What does the release of 5-HT, dopamine and GABA cause?
Decreases appetite
What does zimelidine do?
Inhibits the reuptake of 5 - HT from the synaptic cleft, allowing 5-HT to persist in the Synaptic cleft
What other inputs control feeding behaviour?
- Orexigenic and anorexigenic neurotransmitters have been found in the hypothalamus
- Orexigenic neurotransmitters: ↑appetite
- Anorexigenic neurotransmitters: ↓ appetite
Higher functions can modulate the CNS and peripheral cues what does this cause as a result?
inhibition or stimulation of food intake
What overall factors affects how much we eat?
- Food preferences
- Emotions
- Environment
- Life style
- Circadian rhythm – limits food intake to certain times (in some people)
- Individual-based requirements (e.g., neural, metabolic, and hormonal) may alter feeding behaviour
What receptors does blood glucose stimulate?
Stimulates gluco-receptors in hypothalamus
What do glucostat receptors detect
o ↓[glucose]blood →induces hunger
o ↑[glucose]blood → induces satiety
Why do diabetic patients feel hungry despite ↑[glucose]blood?
- Cold environments stimulate feeding while hot environments inhibit appetite
- Afferent input
- Distension of a full stomach inhibits appetite; contraction of an empty one stimulates appetite
Describe what happens when the pancreas releases?
- Insulin is released.
- Transported to the brain capillaries
- Causes a catabolic reaction so we get reduced food intake and reduce body fat/ or an anabolic reaction occurs and we get increased food intake and increase body fat
- Produces white fat
Describe the regulation of energy homeostasis
On image
Where is leptin produced?
How does it work?
What are the results of leptin secretion?
- Fat cells (adipocytes) secrete leptin (16kDa protein) - gene expressed mainly in adipocytes
- Controls fat stores by operating a feedback mechanism between adipose tissue and brain
- ↑ adipose tissue size → ↑ leptin secretion: High correlation of leptin levels with body fat in humans and animals
- Administration of leptin can decrease food intake, induce weight loss and increase energy expenditure
Where is ghrelin released?
When are ghrelin levels high and low?
What does release of gherlin increase?
When can ghrelin be inhibited by?
• Released by stomach, pancreas, adrenals in response to nutritional status
Circulating levels of ghrelin ↑ preprandially and ↓ after a meal
• Increases central orexins, e.g. NPY, and AgRP (generate hunger signals)
• Secretion of ghrelin can be inhibited by leptin
• Suppresses the ability of leptin to stimulate anorexigenic factors
• Could loss of ghrelin activity determine the success of gastric bypass?
• Leptin and ghrelin act reciprocally on food intake
• Stimulation of their receptors in hypothalamus → changes in food intake
Where is Obestatin released and what does it cause?
• Produced by epithelial cells of stomach
• Encoded by ghrelin gene, but it opposes the effects of ghrelin on food intake
Suppresses food intake (suppresses appetite; ↓ body weight gain)
Antagonises ghrelin-induced food intake (and growth hormone secretion)
• Obestatin mediates its effects via different receptors to ghrelin
• Imbalance of ghrelin and obestatin may have a role in obesity?
[Decreased ghrelin/obestatin ratio characterise obesity in women?]
