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Gastro 2 > Appetite > Flashcards

Appetite Flashcards

1
Q

What are the 3 factors that control thirst?

A

Blood fluid osmolality
Reduced blood volume
Reduced blood pressure

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2
Q

What is osmolality?

A

Concentration of solute in 1Kg of solvent

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3
Q

What is osmolarity?

A

Concentration of solute in 1L of solvent

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4
Q

What is the most potent stimulus for thirst?

A

Reduced blood osmolality

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5
Q

Which 2 regions of the hypothalamus are osmoreceptors found in?

A

Organum vasculosum of the lamina terminals
Subfornical organ

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6
Q

How do osmoreceptors respond to hypertonic plasma?

A

1) Cell shrinks
2) Increases proportion of active cation channels resulting in increasing positive charge influx which depolarises the membrane
3) Sends signals to the ADH producing cells to increase ADH
4) Leads to fluid retention and invokes drinking

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7
Q

How do osmoreceptors respond to hypotonic plasma?

A

1) Cell expands
2) Decreased proportion of active cation channels resulting in decreased positive charge influx so less depolarisation the membrane
3) Inhibit signals to the ADH producing cells so decreased ADH
4) Leads to fluid loss and invokes urination

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8
Q

How can over drinking cause a problem?

A

There is a delay between water absorption in GI tract and plasma osmolality correction as water circulates around the body
Kidney can expel excess water but wastes energy and can interfere with nutrient absorption as it is sodium driven

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9
Q

How is the sensation of thirst initially satiated?

A

Receptors in mouth, pharynx, oesophagus are involved in the relief of the thirst sensation in the short term

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10
Q

When is the sensation of thirst completely satisfied?

A

When plasma osmolality has decreased/ blood volume corrected/ arterial pressure corrected

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11
Q

What 2 drugs are important in the renin-angiotensin aldosterone system?

A

Direct renin inhibitors
ACE inhibitors
(Both used to treat blood pressure)

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12
Q

How does the body try to gain weight if fat mass is reduced?

A

Sympathetic NS energy activity decreased
Energy expenditure decreased
Hunger/food intake increases
Thyroid activity decreased

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13
Q

How does the body try to reduce weight if fat mass is increased?

A

Increasing sympathetic nervous system activity
Increasing energy expenditure
Decreased hunger/food intake

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14
Q

Where does appetite regulation occur?

A

Hypothalamus

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15
Q

What peripheral stimuli are there involved in appetite regulation?

A

Ghrelin, PYY and other gut hormones
Neural input from the periphery and other brain regions
Leptin

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16
Q

How are ghrelin, PYY and other gut hormones involved with appetite regulation?

A

Communicate through the vagus nerve to brainstem
Brainstem communicates with hypothalamus
Hypothalamus communicated with higher CNS regions like amygdala

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17
Q

How does the hypothalamus sensitise a response?

A

By increasing or decreasing energy expenditure and food intake

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18
Q

What is the arcuate nucleus?

A

Aggregation of neurones in the medial basal part of the hypothalamus adjacent to the 3rd ventricle

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19
Q

What are the 2 types of neurones in the arcuate nucleus?

A

Orexigenic neurones= appetite stimulating
Anorectic neurones= appetite suppressive

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20
Q

When does the arcuate nucleus decrease food intake?

A

When its pro-opiomelanocortin neurones activate

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21
Q

What is the paraventricular nucleus?

A

Adjacent to the 3rd ventricle
Neurones that project into the posterior pituitary and secrete oxytocin and ADH

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22
Q

What is the paraventricular nucleus involved in?

A

Osmoregulation
Appetite
Stress reaction of the body

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23
Q

What does the lateral hypothalamus do?

A

Produces only orexigenic peptides

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24
Q

What does the ventromedial hypothalamus do?

A

Satiety
Lesions in this region in rats leads to severe obesity

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25
Q

What other hypothalamic factors are involved in appetite regulation?

A

Endocannabinoids
AMP (activated protein kinase)
Protein tyrosine phosphatase

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26
Q

What does the arcuate nucleus do?

A

Brain area involved in regulation of food intake
Integrates peripheral and central feeding signals

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27
Q

How is the BBB like near the arcuate nucleus??

A

Incomplete BBB to allow access to the peripheral neurones

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28
Q

What are the 2 types of neurones in the arcuate nucleus?

A

Stimulatory neurones
Inhibitory neurones

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29
Q

What peptides do stimulatory neurones release?

A

Neuropeptide Y (NPY)
Agouti-related peptide (Agrp)

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30
Q

How do the peptides produced by the stimulatory neurones in the arcuate nucleus stimulate food intake?

A

Increasing NPY signalling
Reducing melanocortin signalling via release of Agrp

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31
Q

What peptides do inhibitory neurones release?

A

Pro-opiomelanocortin

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32
Q

What receptors for 2 other hormones do they have?

A

Leptin and insulin

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33
Q

How are the leptin and insulin receptors in the arcuate nucleus activated?

A

Increase/decrease in of leptin/insulin signalling

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34
Q

What conditions lead to increase food intake through leptin/insulin mechanism?

A

Fasting
Uncontrolled diabetes
General leptin deficiency

35
Q

What does the paraventricular nucleus control?

A

Osmoregulation
Appetite
Stress reaction of the body

36
Q

What does the lateral hypothalamus do?

A

Produces orexigenic peptides

37
Q

What does the ventromedial hypothalamus do?

A

Satiety
(Lesions in this region in rats leads to sever obesity)

38
Q

What other hypothalamic factors are involved in appetite regulation?

A

Endocannabinoids
AMP (activated protein kinase)
Protein tyrosine kinase phosphatase

39
Q

What does the arcuate nucleus do?

A

Involved with food intake
Integrates central and peripheral feeding signals

40
Q

What is the BBB like in the arcuate nucleus and why?

A

Incomplete BBB to allow access to peripheral hormones

41
Q

What peptides do the orexigenic neurones produce?

A

Neuropeptide Y (NPY)
Agouti-related peptide (Agrp)

42
Q

How do orexigenic peptides stimulate food intake?

A

Increasing NPY signalling
Reducing melanocortin signalling via release of Agrp

43
Q

What is Agrp?

A

An endogenous melanocortin receptor antagonist

44
Q

What 2 other hormones have receptors in the arcuate nucleus?

A

Leptin
Insulin

45
Q

What conditions lead to increased food intake through insulin/leptin?

A

Fasting
Uncontrolled diabetes
General leptin deficiency

46
Q

What do circulating factors do when they reach the hypothalamus in the blood?

A

Cross incomplete BBB and penetrate the arcuate nucleus
POMC/NPY/Agrp neurones activate and go to the paraventricular nucleus

47
Q

What 2 other important functions is the arcuate nucleus responsible for besides feeding?

A

Fertility regulation
Cardiovascular regulation

48
Q

What receptors are expressed on paraventricular nucleus?

A

Melanocortin 4 receptors

49
Q

What is a melanocortin?

A

A group of peptide hormones involved in feeding and other functions

50
Q

How does the melanocortin system work?

A

1) Melanocortin 4 receptors are expressed on paraventricular nucleus
2) Agrp neurones release Agrp which acts on MCRP 4 as an antagonist
3) POMC neurones produce melanocortins

51
Q

What is an example of a melanocortin produced by POMC neurones?

A

Alpha-MSH

52
Q

What is the impact of alpha-MSH?

A

MC4R agonist which decreases appetite, weight and food intake

53
Q

What do NPY and Agrp mutations do to appetite?

A

Nothing as they are not involved with appetite

54
Q

What can POMC and MC4R deficiencies cause?

A

Morbid obesity

55
Q

What 3 signals from other brain regions are involved with controlling appetite?

A

Higher centres of the brain
Lateral hypothalamus and ventromedial hypothalamus
Vagus communication

56
Q

How does vagus communication work in controlling appetite?

A

Vagus communication from digestive tract to brain stem
Brain stem to hypothalamus
Hypothalamus to amygdala

57
Q

What is one of the peripheral signals of body homeostasis?

A

Leptin

58
Q

What is leptin?

A

A hormone made by white adipose tissue and enterocytes in small intestines which circulates in plasma

59
Q

Where does leptin act?

A

Receptors in arcuate and ventromedial nuclei

60
Q

What homeostatic mechanisms is leptin involved in?

A

Appetite
Thermoregulation (adipostat mechanism)

61
Q

What is the adipostat mechanism?

A

The body’s thermostat

62
Q

What is an example of the adipostat mechanism?

A

Control of energy expenditure through thermoregulation which keeps an individual’s fat mass in a narrow range despite changes in diet/daily activity

63
Q

How is leptin involved in appetite control?

A

1) Adipose tissue produces circulating hormones (circulating hormones proportional to amount of adipose tissue)
2) Hypothalamus senses concentration of hormones then alters neuropeptides to increase/decrease food intake

64
Q

What is the ob/ob mouse experiment?

A

1) Mouse with mutation has no gene to produce leptin
2) Mouse eats excessively and becomes obese
3) Develops high blood sugar→pancreatic islet enlargement→increased insulin levels

65
Q

What roles does low leptin levels cause in disease?

A

-Development of atherosclerosis through innate immune system (esp complete system)
-Alzheimer’s disease
-Depression

66
Q

What is congenital leptin deficiency

A

Rare genetic disorder
Low leptin levels
Some are born with normal weight but always hungry and constantly eat so gain weight

67
Q

What are serum leptin levels in patients with obesity?

A

Significantly higher as it correlates with percentage body fat

68
Q

What are the 3 main causes of leptin dysfunction?

A

1) Insufficient production of leptin
2) Defect in signalling for leptin release
3) Decreased sensitivity to leptin

69
Q

Is leptin effective as a weight control drug?

A

No

70
Q

What makes us feel full after a meal?

A

Hormones from the gut

71
Q

What secretes GI hormones?

A

Enteroendocrine cells in stomach, pancreas and small bowel

72
Q

What are the 2 important hormones in appetite regulation?

A

Ghrelin= stimulates appetite, increases gastric emptying
Peptide YY= Inhibits food intake

73
Q

When is ghrelin levels the highest?

A

Before meals to help prep food intake by increasing gastric motility and acid secretion
After meals it returns to normal

74
Q

Where is the name ghrelin derived from?

A

Its role as a growth hormone-releasing peptide (GHRE)

75
Q

How does ghrelin work in the hypothalamus?

A

Directly modulates neurones in the arcuate nucleus
Stimulates NPY/Agrp neurones
Inhibits POMC neurones

76
Q

What are the roles of ghrelin?

A

Increases appetite
Regulation of reward, taste sensation, memory and circadian rhythm

77
Q

What is the correlation between ghrelin and age?

A

Ghrelin levels increase with age

78
Q

What is the effect of ghrelin on food intake?

A

More ghrelin correlates with increased food intake

79
Q

What is peptide tyrosine tyrosine (PYY)?

A

Short peptide released in terminal ileum and colon in response to feeding

80
Q

What does PYY do?

A

Reduces appetite (digested or IV)

81
Q

How does PYY act in the hypothalamus?

A

Inhibits NPY release
Stimulates POMC neurones

82
Q

What causes PYY release?

A

Food arriving in the terminal ileum and colon

83
Q

What food types increase PYY release?

A

Dietary fibres
Wholegrains
Enzymatic breakdown of crude fish proteins

Gastro 2 (11 decks)

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