Appetite Flashcards
1
Q
What are the 3 main triggers of the control of thirst?
A
- plasma osmolality
- reduced blood volume
- reduced blood pressure
2
Q
What is the most potent stimulus for thirst control?
A
Plasma osmolality
3
Q
What change in plasma osmolality is required to induce thirst?
A
2-3%
4
Q
What change in blood volume/arterial pressure is required to induce thirst?
A
10-15%
5
Q
How does the body regulate osmolality?
A
Anti-diuretic hormone (ADH)/vasopressin
6
Q
Where does ADH act?
A
- on the kidneys to regulate the volume and osmolality of urine
- collecting duct, V2 receptor
7
Q
What happens when ADH is low?
A
large volumes of urine is excreted (water diuresis)
8
Q
What happens when ADH is high?
A
small volumes of urine are excreted (anti-diuresis)
9
Q
Where is ADH stored?
A
in the posterior pituitary gland
10
Q
How does the body measure osmolality?
A
via osmoreceptors in the hypothalamus
11
Q
What are osmoreceptors? DELETE
A
- sensory receptors
- involved in osmoregulation
- found in the hypothalamus
12
Q
Where are osmoreceptors in the hypothalamus?
A
- Organum vasculosum of the lamina terminalis (OVLT)
- Subfornical Organ (SFO)
13
Q
How is ADH release regulated in a dehydrated condition?
A
- cells shrink when plasma is more concentrated
- the proportion of cation channels increases, and the membrane depolarizes
- sends signals to ADH producing cells to increase ADH
- fluid retention, invokes drinking
14
Q
How is ADH release regulated in a hydrated condition?
A
- cells expand when plasma is less concentrated
- cation channels are inhibited, the membrane is hyperpolarised
- inhibits signals
- excretion of fluid
15
Q
What causes a decrease in thirst?
A
drinking
16
Q
What detects that drinking has occured in order to stop thirst?
A
receptors in the mouth, pharynx and oesophagus
17
Q
When is thirst completely satisfied?
A
when plasma osmolality is decreased or blood volume/arterial pressure is corrected
18
Q
What type of relief is provided by mouth/pharynx/oesophagus receptors?
A
temporary
19
Q
What else can prompt thirst?
A
- habit
- cravings
- desire
20
Q
What are the negatives of excessive fluid consumption?
A
- energy wastage
- decreased plasma osmolarity
- interference with nutrient absorption (dependent/driven by sodium)
21
Q
What system responds to changes in blood pressure/volume?
A
the renin-angiotensin-aldosterone system
22
Q
What happens when blood pressure drops?
A
juxtaglomerular apparatus secretes renin
23
Q
Where is the juxtaglomerular apparatus?
A
The hilus of the glomerulus
24
Q
What happens when renin is released?
A
activates the renin-angiotensin system by cleaving angiotensinogen into angiotensin I
25
What secretes angiotensinogen?
the liver
26
What happens to angiotensin I?
it is converted into angiotensin II by (angiotensin converting enzyme) in the lungs
27
What is the effects of angiotensin II?
- induces thirst
- release of aldosterone
- ADH secretion
- vasoconstriction (increased sympathetic activation)
28
What does aldosterone do?
```
Influences:
- sodium reabsorption
- potassium excretion
and therefore,
- water retention
```
29
What happens when there is a reduction in fat mass?
- increase in food intake
- reduction in energy expenditure
- reduces the effect of the thyroid gland
- sympathetic inhibition
30
What happens when there is adipose tissue expansion?
- reduces food intake
- increases energy expenditure
- sympathetic activation
31
What is the impact of changes in adipose tissue?
activates responses that favour the return to the previous/original weight
32
Which part of the brain regulates hunger?
hypothalamus
33
What are the 2 main gut hormones involved in appetite regulation (peripheral signalling)?
- Ghrelin
- PYY
34
What is the long term hormonal appetite regulation?
leptin system
35
What are the 3 main factors involved in appetite regulation?
- Ghrelin/PYY
- neural input from periphery/other brain regions
- Leptin
36
What does orexigenic mean?
appetite stimulant
37
What does anorectic mean?
appetite supressive
38
What is the role of the arcuate nucleus?
- regulation of food intake
- both orexigenic and anorectic
- integrates peripheral and central feeding signals
39
How does the arcuate nucleus allow access to peripheral hormones?
Incomplete blood-brain barrier
40
What are the two neuronal populations of the arcuate nucleus?
- stimulatory NPY/AGRP neuron
- inhibitory POMC neuron
41
What is the role of the paraventricular nucleus?
- neurones to the posterior pituitary (oxytocin)
- regulates appetite
42
What is the role of the lateral hypothalamus?
produces orexigenic peptides
43
What is the role of the ventromedial hypothalamus?
satiety
44
What is the effect of lesions in the ventromedial hypothalamus?
severe obesity
45
What is the effect of arcuate nucleus pro-opiomelanocortin (POMC) neurones?
reduced food intake
46
What is also thought to be implicated in appetite regulation?
- endocannabinoids
- AMP (activated protein kinase)
- protein tyrosine phosphokinase
47
Where are NPY/Agrp neurones found?
only in the arcuate nucleus
48
How do NPY/Agrp neurones stimulate food intake?
make peptides that:
- increase NPY signaling
- reducing melanocortin signaling
by AGRP release
49
What is ARGP?
an endogenous melanocortin receptor antagonist
50
What can activate NPY/Agrp neurones?
decrease in:
- leptin
- insulin
51
What conditions cause an increase in food intake by impacting the NPY/Agrp neurones?
- fasting
- uncontrolled diabetes
- genetic leptin deficiency
52
What is the arcuate nucleus involved in?
- feeding
- fertility
- cardiovascular regulation
53
What is in the central melanocortin system?
- NPY
- AGRP neurones
- POMC
54
What are melanocortins?
products of the POMC
55
What is an example of melanocortin
alpha-MSH
56
What is the role of the central melanocortin system?
central regulator of energy balance
including:
- feeding behaviours
- energy expenditure
57
Where are melanocortin-4 receptors expressed?
paraventricular nucleus
58
What stimulates melanocortin-4 receptors?
serotonin
59
What is the effect of the stimulation of melanocortin-4 receptors?
- reduction of appetite
- weight loss
- reduced food intake
60
What has a encouraging/stimulating effect on melanocortin-4 receptor?
alpha-MSH
61
What has a inhibiting effect on melanocortin-4 receptor?
Agrp
62
What is the effect of Agrp and NPY mutations?
No associated effects to appetite
63
What is the effect of POMC deficiency and MC4-R mutations?
causes morbid obesity
64
What role does the amygdala play?
controls reward related motivation pathways, affects appetite
65
How is neural information from the digestive tract passed on to the hypothalamus?
carried by the vagus to the brain stem and eventually the hypothalamus
66
What is the adipostat mechanism?
- circulating hormones are produced by adipose tissue (more=more hormone)
- concentration sensed by the hypothalamus
- hypothalamus alters neuropeptides to change food intake
67
What produces leptin?
- adipocytes in white adipose tissue
- enterocytes
68
What does leptin do?
- acts on the hypothalamus
- decreases appetite (intake)
- increases thermogenesis (expenditure)
69
When is leptin low or high?
- low when low body fat
- high when high body fat
70
Where in the hypothalamus does leptin act?
- arcuate nuclei
- ventromedial nuclei
71
What is the role of leptin?
- regulation of adipose tissue mass
- development of atherosclerosis (innate system)
72
What conditions have been associated with low levels of leptin?
- Alzheimer's disease
- Depression
73
What happens in congenital leptin deficiency?
RARE
morbid/severe obesity
low serum leptin levels
74
How can congenital leptin deficiency be managed?
leptin replacement to reduce body weight
75
What happens to serum leptin in obesity?
- serum leptin concentration is correlated to the body fat %
- obesity due to leptin resistance
76
What are the mechanisms of leptin in obesity?
- absent leptin
- leptin resistance
- regulatory defect in leptin (signalling issue)
77
Would leptin be an effective weight control drug?
No, due to leptin resistance
78
What reduces hunger after a meal?
hormonal signalling from the gut
79
What secretes gut hormones?
enteroendocrine cells in:
- stomach
- pancreas
- small intestine
80
What are the roles of the gut hormones?
- motility regulation
- appetite regulation
- satiety
- salivation
81
What is the effect of Ghrelin?
- stimualtes appetite
- increases gastric emptying
82
What is the effect of Peptide YY?
inhibits food intake
83
When is Ghrelin highest?
- before meals
- increases gastric motility and acid secretion
- prepares for food intake
84
What impact does Ghrelin have in the hypothalamus?
- stimulates NPY/Agrp neurones
- inhibits POMC neurones
85
What does Ghrelin regulate?
- reward
- taste sensation
- memory
- circadian rhythm
- increases appetite
86
What rhythm is seen by Ghrelin levels?
diurnal rhythm
87
What does circulating Ghrelin correlate with?
- time of day
- positive with age
88
What is the physiological role of Ghrelin?
meal initiation
89
Where is Peptide tyrosine tyrosine (PYY) released?
- terminal ileum and colon
- response to feeding
90
What is the effect of PYY in the hypothalamus?
- stimulates POMC neurones
- inhibits NPY release
91
What types of food trigger PYY release?
- dietary fibres
- wholegrains
- enzymatic breakdown of crude fish proteins
92
What does PYY do?
induces satiety/reduces appetite
93
What is the degree of PYY release proportional to?
calorie intake
94
What are the side effects of PYY?
- nausea
- fullness
- less hunger
- early fullness
95
What co-morbidities are associated with obesity?
- depression
- stroke
- sleep apnoea
- MI
- hypertension
- diabetes
- bowel cancer
- osteoarthritis
- peripheral vascular disease
- gout
96
Which factors are most dominant in terms of increasing risk of obesity?
environmental factors and genetic predisposition
