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Gastrointestinal > Control of Food Intake > Flashcards

Control of Food Intake Flashcards

(103 cards)

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1
Q

What enables food to be stored in the stomach?

A

The autonomic nervous system enables involuntary food storage in the stomach

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2
Q

What is the role of the ANS?

A

ANS controls bodily functions unconsciously

e.g. breathing, heartbeat and digestive processes

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3
Q

What is satiety?

A

When food is present in the gut - full sensation

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4
Q

What is stomach emptying?

A

Elicits hunger

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5
Q

What controls gut motility and accommodation?

A

There are factors present in the gut that are important in the control of gut accommodation and motility / emptying ∴ energy fluxes

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6
Q

What is the role of ghrelin?

A

Secreted by fundus
Increases sense of hunger stimulating gastric emptying
- stimulates NPY and AgRP

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7
Q

What is the role of PYY?

A

Opposes ghrelin

signals satiety, inhibits gut motility / emptying

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8
Q

What is the role of amylin?

A

Helps reduce food intake through medulla of brain stem by delaying gastric emptying

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9
Q

What is an enterogastrone?

A

Hormones secreted by duodenum mucosa in response to dietary lipids
- inhibit aboral motion of chyme

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10
Q

Name some enterogastrones

A

CCK (cholecystokinin)
GIP (gastric inhibitory peptide)
secretin

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11
Q

What regulates gastric relaxation?

A

The relaxation of the gastric reservoir is regulated mainly by reflexes

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12
Q

How is gastric reservoir relaxed?

A 
Inhibitory vagal fibres release ACh 
Activating inhibitory anteric pathways that release:
- NO
- VIP
- PACAP
- and/or ATP

in order to relax muscle

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13
Q

What are the 3 types of relaxation that occur in the gastric reservoir (stomach)?

A
  1. Receptive relaxation
  2. Adaptive relaxation
  3. Feedback relaxation
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14
Q

What stimulates receptive relaxation?

A

Mechanical stimulation of pharynx via mechanoceptors / sight

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15
Q

What causes adaptive relaxation?

A

Vagal innervation via NO / VIP

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16
Q

What stimulates feedback relaxation?

A

Nutrients and enterogastrones (CCK)

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17
Q

What regulates the relaxation mechanisms of the stomach?

A

The receptive, adaptive and feedback relaxation of the stomach are mediated by NANC mechanisms (e.g. NO / VIP, PACAP etc.) and by reflex chains including the release of NA

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18
Q

What is PACAP?

A

pituitary adenylate cyclase - activating peptide

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19
Q

Where is PACAP found in the body?

A

isolated from the pituitary -> stimulates AC in anterior pituitary

High levels in the brain and gut
- myenteric and submucosal ganglia

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20
Q

What is the function of PACAP?

A

Mediates neuronal regulation of gastric acid secretion and intestinal motility

Stimulates relaxation of colonic smooth muscle

Stimulates pancreatic secretions; insulin + glucagon

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21
Q

What is a vagotomy?

A

Surgical procedure involving the removal of part of the vagus nerve

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22
Q

What is the effect of a vagotomy?

A

Vagotomy impairs:

  • accommodation
  • gastric compliance
  • emptying

can be a cause of early satiety in some patients

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23
Q

What causes gastroparesis?

A

Prior gastric surgery

Non motor factors may also be involved as symptoms don’t always correlate with delays in gastric emptying

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24
Q

What is gastroparesis?

A

Delayed gastric emptying

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25
What is gastric compliance?
Accommodation and perception of gastric distension
26
What effect will a vagotomy have on gastric compliance?
Denervation will have little to no effect; Peripheral signals from adrenals The pancreas, adipose tissue, GIT and CNS will continue to operate to control food intake and energy expenditure
27
What is hunger?
Discomfort caused by a lack of food and desire to eat | A strong physical craving for food / sensation of emptiness in the stomach
28
What is appetite?
A psychological desire / drive to satisfy body's need for food (hunger stimulated response) - can have an appetite and not be hungry (+ vice versa) - due to stress or illness
29
What is satiety?
State of being full after eating food
30
What is Aphagia?
The inability / refusal to swallow
31
How do hunger and satiety work together?
Hunger and satiety are cues that tell you when to stop and start eating Satiety signals prolong the interval until hunger or the onset of the next meal
32
What is hunger and satiety dependent upon?
Hypothalamic control and BMI (70% due to genes)
33
What is BMI?
Body mass index | each individual has a genetically determined weight + height set point
34
What regulates weight and BMI?
Body weight and BMI are tightly regulated by an energy homeostatic mechanism
35
What influences appetite?
- family gatherings - food palatability - emotional - habitual - circadian rhythms
36
What role does the hypothalamus play in control of food intake?
Hypothalamus is the control centre of food intake and appetite -> controls hunger and thirst
37
What enables the hypothalamus to carry out its functions?
The hypothalamus base contains several nuclei that regulate energy homeostasis -> control appetite; size of helping + ingestive behaviour
38
Describe the features of the prefrontal cortex that aid its role in controlling food intake
- 'food seeking' - Integrates sensory info from inside and outside body - receives emotional + cognitive info from limbic system - intimately related to cortical areas involved in motor planning and execution - translates all homeostatic + environmental info into adaptive behavioural responses
39
What is the limbic system?
Complex system of nerves and networks in the brain
40
Where is the prefrontal cortex found?
Covers front part of frontal lobe in the brain
41
What is the role of the limbic system?
- areas concerned with instinct and mood - controls emotions, fear, pleasure, anger, also drives hunger, sex, dominance, care of offspring etc.
42
Which hypothalamic nuclei are involved in modulating feeding behaviour?
- Lateral hypothalamus (LH) - Ventromedial Nucleus (VMN) - Dorsomedial Nucleus (DMN) - Paraventricular Nucleus (PVN) - Accurate Nucleus - Suprachiasmatic Nucleus
43
What is the specific role of the lateral hypothalamus?
LH is the hunger / thirst centre
44
What is the role of the VMN?
Ventromedial nucleus is the satiety centre
45
What is the significance of the LH and VMN?
LH and VMN both have the ability to restrain feeding if required lesion of VMN leads to increased appetite, with weight gain that persists
46
What is the function of the DMN?
Modulates energy intake hunger centre Releases NPY into DMN to increase feeding
47
What is the function of the PVN?
Modulates feeding behaviour PVN and perifornical hypothalamus control feeding behaviour NPY, opioids, GABA etc. increase feeding Leptin decreases food intake
48
What is the function of the Accurate nucleus?
Neurons produce orexigenic signals: - NPY - opioids - dynorphin - ꞵ-endorphin - POMC - amino acids - GABA - glutamate
49
What is the role of the Suprachiasmatic nucleus?
Location of human body clock - circadian rhythms control - perception of light-dark cycle - hunger / appetite sensation individual based requirements (neuronal, hormonal, metabolic) may affect feeding behaviour
50
What is the significance of the Serotonin 5-HT(2C) and 5-H(1A) receptors?
5-HT(2C) and 5-HT(1A) Serotonin ligand receptors are critical in the regulation of food intake - stimulate appetite - suppress appetite
51
How do 5HT receptors stimulate appetite?
Appetite stimulating neurons release AgRP and NPY MC4R isn't occupied -> so appetite is stimulated
52
How do 5HT receptors suppress appetite?
Appetite suppressing neurons release POMC POMC broken down into ꭤ-MSH ꭤ-MSH binds to MC4R which suppress appetite
53
What is mCPP?
meta-Chlorophenylpiperazine is a psychoactive drug that suppresses appetite
54
Explain how mCPP suppresses appetite?
1. mCPP binds to 5HT(2C) receptors on appetite suppressing POMC neurons 2. Activates POMC neurons to release ꭤ-MSH 3. ꭤ-MSH binds to MC4R to suppress appetite
55
Describe the diurnal variation in food intake
- Carbohydrates metabolised during the day - Fats metabolised at night - Hypothalamus responds to switch between carbohydrate and fat metabolism
56
How does Zimeldine suppress appetite?
Inhibits the re-uptake of 5HT from the synaptic cleft | 5HT persists and is able to mediate its effects in suppressing appetite
57
What are the side effects of Zimeldine?
- dry mouth - increased sweating - vertigo - nausea
58
Where is the satiety centre located?
The ventromedial hypothalamus (VMN)
59
What does the stimulation of VMN cause?
aphagia
60
What is the effect of VMN lesions?
hyper-aphagia
61
Where is the hunger centre in the body?
The lateral hypothalamus (LH)
62
What is the effect of LH stimulation?
increased feeding
63
What does lesions of LH cause?
aphagia
64
What factors increase appetite?
opioids | growth hormone releasing hormones
65
What is the effect of the opioid antagonist naltrexone?
Reduces the positive 'hedonic valence' of food
66
What is the role of orexigenic neurotransmitters?
increase appetite
67
What is the function of anorexigenic neurotransmitters?
decrease appetite
68
Where are orexigenic and anorexigenic neurotransmitters found?
the hypothalamus
69
What controls nutrient intake?
Signals from the periphery CNS controls nutrient intake
70
What modulates responses to the CNS and Periphery?
Higher centres
71
What environmental factors affect food intake
- food preferences - emotions - lifestyle - environment - circadian rhythm
72
Which receptors detect blood glucose?
[glucose]blood stimulates glucoreceptors in the hypothalamus
73
What is the effect of increased Blood glucose?
Upregulation of satiety
74
What is the effect of decreased blood glucose?
upregulation of hunger
75
Why do diabetics feel hungry despite high blood glucose?
Diabetic patients feel hungry due to the lack of insulin present to decrease feeding behaviour Individuals with insulin dependent diabetes melilitus (IDDM) are hyperphagic
76
Explain IDDM patients are very rarely obese?
Aren't obese because insulin is required for adipocytes to store fat Excess calories consumed are wasted via inefficient utilisation via urine excretion
77
What is calcitonin?
A hormone produced by the thyroid gland, involved in appetite reduction
78
How does temperature affect appetite?
Cold environments stimulate feeding | Hot environments inhibit appetite
79
How does the stomach regulate appetite?
Distension of a full stomach inhibits appetite Contraction of an empty stomach stimulates appetite Deposition of fat may control appetite via leptin
80
Explain the effect of hormones on inhibiting food intake
CCK and somatostatin inhibit further food intake via vagus nerve
81
Which pancreatic hormone helps regulate food intake and how?
Insulin is secreted into blood from the pancreas in direct proportion to the amount of fat stored in white adipose tissue
82
How is insulin transported to the brain?
As insulin circulates through brain capillaries, a small amount of insulin is transported into the brain where it acts on insulin receptors on neurons with either: - net catabolic activity - net anabolic activity
83
How do neurons and insulin receptors influence energy homeostasis?
These neurons influence - energy expenditure - food intake - amount of fat stored in body by exerting a net catabolic action
84
What effect does insulin have in adipocytes?
Insulin inhibits lipolysis in adipocytes
85
What induces lipolysis?
``` Gherlin Noradrenaline Adrenaline Growth Hormone Testosterone Cortisol ```
86
Which hormones secreted by the endocrine pancreas regulate energy homeostasis?
Insulin, glucagon, amylin | - these are anorexigenic agents
87
What is the function of insulin?
Reduces energy intake and suppresses hepatic glucose production by acting on the liver and forebrain
88
What is the effect of glucagon?
Acts mainly at liver where it increases glucose production while generating a signal to reduce energy intake -> relayed to hindbrain
89
Where does amylin produce its effect?
Amylin acts directly on the hindbrain to reduce energy intake NTS and Area Prostrema (AP) indicate stimulation
90
What is the area Prostrema?
medularly structure controlling vomiting and ANS functions in the CNS
91
What is the effect of leptin?
Administration can decrease food intake, induce weight loss and increase energy expenditure by increasing the expression of anorexigenic factors e.g. POMC, CART, cocaine and CRH
92
How does adipose tissue size affect leptin secretion?
Increased adipose tissue size = increased leptin secretion
93
Explain how insulin and leptin work together
Insulin and leptin act agonistically in reducing food intake via action on receptors in brain
94
What is the effect of increased leptin/insulin?
increased anorexigenic factors - increased energy expenditure - increased thermogenesis - diminished food intake
95
What is the effect of decreased leptin/insulin?
increased orexigenic pathways - low metabolic rate - enhanced appetite
96
How are leptin effects inhibited?
Binge eating (obesity) and Hyperaphia
97
Explain the relationship of leptin and body fat
High correlation of leptin levels with body fat in humans | Hyperaphia and severe obesity occur with leptin deficiency or leptin receptor defects
98
Outline the features of ghrelin
- fast acting - stimulates food intake; orexigenic agent - released by stomach, pancreas, adrenals in response to nutritional status - circulating ghrelin levels increased, preprandial and decreased after a meal
99
How does ghrelin induce food intake?
Increases central orexins (NPY and AgRP) to generate hunger signals Suppresses leptin's ability to stimulate anorexigenic factors
100
What inhibits ghrelin secretion?
leptin
101
What are the effects of obestatin?
suppresses food intake | antagonises ghrelin induced food intake
102
How does obestatin mediate its effects?
Via different receptors to ghrelin - encoded by ghrelin gene but opposing effects produced
103
Where is obestatin produced?
By stomach epithelial cells

Gastrointestinal (18 decks)

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