control of food intake Flashcards
What organs make up the GI tract?
• Mouth • Oesophagus • Stomach • Small intestine • Large intestine • Anus Note: the liver, pancreas and gallbladder are part of the digestive system but DO NOT form the GI tract
How is the food stored in the stomach?
ANS (autonomic nervous system) enables the storage of food in the stomach
What are the 3 control factors important for accommodation (decrease in gut motility)?
VIP (vasoactive intestinal peptides)
NO (nitric oxide)
PYY secreted by the pancreas
What is the 1 control factor important for emptying of the GI tract, which results in the feeling of hunger?
Ghrelin
What is Ghrelin?
Ghrelin is secreted by the stomach fundus and increases the sense of hunger and stimulates gastric emptying
There are many mediators involved in the relaxation of the stomach during accommodation. Describe these mediators and their mechanisms in detail.
The relaxation of the gastric reservoir is mainly regulated by reflexes. Three kinds of relaxation are:
1. Receptive relaxation (from mechanical stimulation of the pharynx mechanoreceptors)
2. Adaptive relaxation (inhibitory vagal fibre via NANC inhibition)
3. The inhibitory vagal fibres release Ach, activating inhibitory pathways which release NO, PACAP, VIP, and/or ATP in order to relax
Feedback relaxation (CCK and nutrients)
What is a vagotomy?
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).
This process reduces:
• Accommodation
• Gastric compliance
What are potential changes that occur in the functioning of the GI tract due to a vagotomy?
• Nausea • Easy filling • Bloating • Early satiety However, this is not common due to the fact that satiety is controlled primarily by the ANS rather than the physical size of the stomach.
Define hunger
it is the discomfort caused by the lack of food and the desire to eat - a strong craving/ drive for food/ sensation of emptiness in the stomach
Define appetite
the desire/ desire to satisfy the body’s needs for food - a hunger-stimulated response
Define satiety
the 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)
Hunger, satiation and satiety are cues that tell you when to start and stop eating
• Hunger tells you to start eating
• Satiation tells you to stop eating
Satiety is the satisfaction between meals
Give a summary of the factors that influence food intake
Hypothalamic control: balance of stimulating and inhibiting forces in the hypothalamus regulates feeding
What is the reason for people having different BMIs?
- Genes accounts for 70% of the reason
2. How much we eat and its composition
What factors are appetite influenced by?
• Family gatherings
• Food palatability (food preference)
• Emotional (stress, anxiety, depression)
• Habitual (lifestyle)
• Environment
• Circadian
Limits food intake to certain times (in some people)
Explain the mechanism by which the hypothalamus controls food intake
The hypothalamus is the control centre for appetite and food intake (controls hunger and thirst)
The base of the hypothalamus has several nuclei that regulate energy homeostasis. This controls the appetite, size of helping and our ingestive behaviour
What is the role of the prefrontal cortex and limbic system in the control of food intake?
Pre frontal cortex: food-seeking
• Integration of sensory information from inside and outside the body
• Receives emotional and cognitive information from the limbic system
• Helps one to make choices by translating all of the homeostatic and environmental information into adaptive behavioural response
Limbic system: complex system of nerves and networks in the brain; areas concerned with instinct and mood. May control emotions such as pleasure, fear, anger etc
• The satiation of feeding behaviour is associated with motor planning and execution
Cortico-limbic mechanisms of reward are under executive control
What is the limbic system?
This is a complex system of nerves and networks in the brain. It involves area around the cortex concerned with instinct and mood.
It has control over the following emotions: fear, pleasure, anger; it also drives hunger, sex, dominance, care of offspring, etc.
Feeding behaviour/food intake is modulated by many hypothalamic sites.
List some of them
1) Lateral Hypothalamus (LH) = hunger centre
2) Ventromedial Nucleus (VMN) = satiety centre
Ventromedial nucleus and lateral hypothalamus
• Has the ability to restrain feeding if required
3) Dorsomedial Nucleus (DMN) = modulates energy intake (hunger centre)
releasing NPY into the DMN = increases feeding
4) Paraventricular Nucleus (PVN) = modulates feeding behaviour
Paraventricular nucleus and perifornical hypothalamus
• controls feeding behaviour
• NPY, opioids, GABA etc increases feeding
• Leptin decreases food intake
5) Arcuate Nucleus (ARC) neurons produce orexigenic signals: • NPY • Opioids • Dynorphin • B-endorphin • POMC • Galanin • Amino acids • GABA Glutamate
What can a lesion of the VMN result in?
Increases appetite
Weight gain that tends to persist
Where is the suprachiasmatic nucleus located and what is its function?
Nuclei in the hypothalamus
It is responsible for controlling circadian rhythms
Describe the regulation of appetite in the hypothalamus by the 5-HT2C agonist
Appetite is regulated by the balance between an appetite-stimulating pathway that releases agouti-related peptide (AgRP) and neuropeptide Y (NPY), and an appetite suppressing pathway that releases α-melanocyte stimulating hormone (α-MSH).
The appetite suppressing neurons make the precursor pro-opiomelanocortin (POMC), which is broken down into α-MSH, which in turn binds to melanocortin 4 receptors (MC4R) to suppress the appetite. When there is no occupancy of MC4R receptors by α-MSH, there is stimulation of the appetite.
A serotonin 5-HT2C agonist, such as meta-chlorphenylpiperazine (mCPP), hypothetically binds to 5-HT2C receptors on POMC neurons in the appetite suppressing pathway, activating POMC neurons and leading to the release of α-MSH, which binds to MC4R to suppress the appetite.
Name a 5-HT2C agonist and describe its function in the control of food intake
mCPP (meta-chlorphenylpiperazine)
A serotonin 5-HT2C agonist, such as meta-chlorphenylpiperazine (mCPP), hypothetically binds to 5-HT2C receptors on POMC neurons in the appetite suppressing pathway, activating POMC neurons and leading to the release of α-MSH, which binds to MC4R to suppress the appetite.
