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Gastroenterology > Appetite > Flashcards

Appetite Flashcards

1
Q

What are the three main stimuli in regulation of thirst?

A

body fluid osmolality
a reduced blood volume
a reduced blood pressure

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2
Q

What is the most potent stimulus?

A

changes in plasma osmolality

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3
Q

How does the body regulate osmolality?

A

Via anti diuretic hormone

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4
Q

What is the mechanism of action of ADH?

A

Mediates it effect via V2 RECEPTORS
increases the transcription and insertion of aquaporin -2 into the apical membrane of the collecting duct
this allows water to move down the osmotic gradient

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5
Q

What is water diuresis?

A

when plasma ADH is low a large volume of urine is excreted

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6
Q

What is anti diuresis?

A

when plasma ADH is high a small volume of urine is excreted

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7
Q

Where is ADH stored in the body?

A

the posterior pituitary gland

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8
Q

What are osmoreceptors?

A

sensory receptors found in the hypothalamus mediating osmoregulation

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9
Q

Which regions of the hypothalamus are osmoreceptors found in?>

A

the organum vasculosum of the lamina terminalis and the subfornical organ

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10
Q

How do osmoreceptors mediate the release of ADH?

A
  1. increase is plasma concentration results in hypertonic stimulation leading to cell shrinkage

the proportion of cation channels increase -> resulting in membrane depolarisation

the depolarisation is converted into signal which stimulate the posterior pituitary to release ADH

fluid retention invokes drinking

  1. decrease in plasma concentration results in hypotonic stimulation leads to cell swelling

proportion of cation channel decreases resulting in hyperpolarisation of the membrane

reduced signalling to the posterior pituitary inhibiting the production of the ADH

reduced fluid retention inhibits the need to drink

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11
Q

How is the sensation of thirst stopped?

A

relief of thirst once plasma osmolality decreases, or blood volume and arterial pressure is corrected

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12
Q

Outline the renin angiotensin system

A
  1. blood pressure drops
  2. the juxtaglomerular cells of renal afferent arteriole secrete renin
  3. renin cleaves angiotensinogen formed in the liver into angiotensin-1
  4. angiotensin 1 is converted by ACE in the lungs into angiotensin 2
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13
Q

What are the physiological effects of angiotensin 2?

A

vasoconstriction, increase sympathetic activity, ADH secretion, aldosterone secretion

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14
Q

How does angiotensin 2 lead to aldosterone release?

A
  1. angiotensin 2 binds to receptors on the intraglomerular mesangial cells
  2. results in contraction of blood vessels around the cells
  3. stimulating the release of aldosterone from the zona glomerulosa of adrenal cortex
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15
Q

What are the physiological effects of aldosterone?

A

h2o retention via NaCL absorptions and k+ excretion

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16
Q

What are common drugs that affect the renin angiotensin system?

A

ACE inhibitors and direct renin inhibitors

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17
Q

What do ACE inhibitors and direct renin inhibitors treat?

A

hypertension

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18
Q

Where does appetite regulation occur?

A

in the hypothalamus

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19
Q

Which gut hormones that travel through the vagus nerve regulate appetite?

A

ghrelin, PYY and other gut hormones

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20
Q

What is the arcuate nucleus?

A

aggregation of neurone in the medial basal part of the hypothalamus involved in the regulation of food intake

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21
Q

How is the arcuate nucleus involved in appetite regulation?

A

produces orexigenic (appetite stimulating) and anorectic (appetite supressing) neurones

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22
Q

What is the paraventricular neurone related to appetite?

A

orexigenic and anorectic neurones project terminally to the paraventricular nucleus

neurones to posterior pituitary -> which stimulate secretion of oxytocin and ADH which affects appetite

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23
Q

Which part of the hypothalamus is associated with satiety?

A

ventromedial hypothalamus - lesions can lead to severe obesity

24
Q

Which part of the hypothalamus is associated with hunger?

A

lateral hypothalamus which produces orexigenic peptides

25
Q

How are melanocortins associated with food intake?

A

food intake decreases when the arcuate nucleus pro opiomelanocortin neurones activate

26
Q

What are some hypothalamic factor implicated in appetite regulation?

A

endocannabinoids
AMP activated protein kinase
protein tyrosine phosphatase

27
Q

Describe the blood brain barrier around the arcuate nucleus

A

incomplete to allow access to hormones in the periphery

28
Q

What are the two neuronal populations in the arcuate nucleus?

A

stimulatory - NPY/ Agrp neuron

inhibitory - POMC neuron

29
Q

What are the breakdown products of POMC?

A

ACTH and MSH

30
Q

What is the function of nPY/Agrp neuron?

A

stimulate food intake by reducing melanocortin via release of Agrp and increase neuro peptide Y signalling

31
Q

How is the NPy/AGRP neuron stimulated?

A

activated by a decrease of leptin or insulin

32
Q

What conditions can result in stimulation of NPY/Agrp?

A

fasting, uncontrolled diabetes, genetic leptin deficiency

33
Q

What other systems is the arcuate nucleus involved in?

A

reproductive fertility and cardiovascular regulation

34
Q

What are melanocortins?

A

products of POMC such as alpha MSH

35
Q

How do melanocortins result in decreased food intake?

A

POMC protein breakdown results in melanocortins such as alpha MSH, which act on the melanocortin 4 receptors via ligand bonding. the receptor can now be acted on by serotonin, which results in reduction of appetite and weight and a decreased food intake

36
Q

What other brain regions also play apart in apetite?

A

amygdala and brain stem

37
Q

What is adipostat?

A

circulating hormone produced by fat

38
Q

What is the adipostat mechanism in apetite?

A

hypothalamus detects increase in concentration of adipostat -> alters neuropeptides to decrease or increase food intake

39
Q

What is the absence of leptin associated with?

A

severe obesity

40
Q

What is the function of leptin?

A

hormone made by adipose cells and enterocytes in the small intestine that inhibits hunger in order to regulate energy balance

41
Q

Where does leptin act on?

A

acts on the hypothalamus regulating appetite and thermogenesis

42
Q

When is leptin low?

A

when there is a low body fat

43
Q

When is leptin high?

A

high body fat

44
Q

What is leptin resistance?

A

leptin circulates in plasma in concentrations proportional to fat mass but does not inhibit hunger appropriately

45
Q

Where are gastrointestinal hormones secreted from?

A

enteroendocrine cells in the stomach, pancreas and small bowel

46
Q

Which hormones regulate appetite regulation gastrointestinally?

A

ghrelin, peptide YY

47
Q

What is the function of ghrelin?

A

increases appetite by directly modulating neurons in the arcuate nucleus. it stimulates npy and agrp neurones, and inhibits pomc neurons

48
Q

How do concentrations of ghrelin change?

A

increase before meal time

and changes with age

49
Q

How does ghrelin change weight?

A

food intake increases leading to excess weight gain

50
Q

What is peptide tyrosine tyrosine PYY?

A

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

51
Q

What effect does PYY have on appetite?

A

reduces appetite - can be digested or injected IV

52
Q

What stimuli affects PYY?

A

food arriving to the terminal ileum and colon

53
Q

How does PYY affect nPY?

A

inhibits NPY release

54
Q

How does PYY affect POMC?

A

stimulates POMC neurons

55
Q

What are the comorbidities of obesity?

A

depression, stroke, sleep apnoea, myocardial infarction, bowel cancer, osteoarthritis, gout, peripheral vascular disease, diabetes, hypertension

Gastroenterology (6 decks)

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