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GASTROENTEROLOGY 2 > APPETITE > Flashcards

APPETITE Flashcards

1
Q

What are the 3 stimulants that control thirst and which one has the greatest effect?

A

Body fluid osmolality - strongest
Blood volume
Blood pressure

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2
Q

What is the function of ADH?

A

Acts on kidneys to regulate volume and osmolality of urine. More ADH = less urine and vice versa

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3
Q

How does the body sense blood osmolality and how does it correct changes?

A

Osmoreceptors:
Cell shrinks when plasma more concentrated
Cation channel proportion increase and cation influx
Membrane depolarisation
Signal sent to neurons of hypopituitary to increase ADH
Fluid retention and drinking

Vice versa

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4
Q

Where are osmoreceptors found?

A

Hypothalamic regions:

  • Organum vasculosum of lamina terminalis (OVLT)
  • Subfornical organs (SFO)
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5
Q

How does temporary relief of thirst come about and why?

A

Receptors in mouth, pharynx and oesophagus sense fluid before it has even been absorbed by the GI tract and causes temporary relief in order to prevent fluid overload

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6
Q

How does complete satisfaction of thirst come about?

A

Only once plasma osmolality is decreased or blood volume/pressure is corrected

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7
Q

How does the body correct low blood pressure/volume?

A

Low BP/BV senses by juxtaglomerular cells of renal afferent arteriole via stretch receptors. Renin is produced which converts angiotensinogen (liver) into angiotensin I. ACE (respiratory organs) then converts angiotensin I to II.

Angiotensin II increases thirst, aldosterone, ADH, vasoconstriction via sympathetic activity

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8
Q

Describe the laws of body weight homeostasis

A 
Reduction in fat mass:
Decreased SNS activity
Increased food intake 
Decreased energy expenditure
Decreased thyroid activity

Adipose tissue expansion:
Increased SNS activity
Decreased food intake
Increased energy expenditure

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9
Q

What signals regulate appetite and where?

A

Ghrelin, PPY and other gut hormones
Neural input from periphery/brain regions
Leptin

Signals to hypothalamus which provides a link between higher brain circuits and stimulus.

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10
Q

What is the definition of orexigenic and anorectic?

A

Orexigenic - appetite stimulant

Anorectic - appetite suppressive

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11
Q

List the regions of the hypothalamus involved in appetite regulation and their roles

A

Paraventricular nucleus - a terminal of NPY/Agrp/POMC neurones, also has neurones which project to hypopituitary

Ventromedial hypo - satiety, lesions here lead to severe obesity

Arcuate nucleus - POMC neurones decrease food intake when activated

Lateral hypo - produces orexigenic peptides

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12
Q

Which region of the hypothalamus is the most important for energy balance?

A

Arcuate nucleus

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13
Q

How is the arcuate nucleus able to integrate peripheral and central feeding signs?

A

Incomplete blood brain barrier allowing access to peripheral hormones

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14
Q

What are the two populations of neurones present in the arcuate nucleus?

A 
NPY/Agrp neurones (stimulates feeding)
POMC neurones (inhibits feeding)
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15
Q

How do the NPY/Agrp neurones work?

A

Makes orexigenic peptides NPY and Agrp

Agrp is a melanocortin receptor antagonist
Both peptides come from the same neurone

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16
Q

What are the effects of leptin on the arcuate nucleus?

A

Leptin stimulates POMC neurones and inhibits NPY/Agrp neurones

17
Q

What is the role of the melanocortin system?

A

Central regulator of energy balance in both feeding behaviour and energy expenditure

It is a collection of central nervous circuits

18
Q

Describe/draw the melanocortin system

A

Agrp and POMC neurones from arcuate nucleus produce Agrp and alpha-MSH (melanocortin) respectively.

These bind to MC4R (melanocortin 4 receptor) on a second order neurone in the paraventricular nucleus

Agrp is a MC4R antagonist
Alpha-MSH is a MC4R agonist

Activation of MC4R causes decreased food intake

19
Q

What are melanocortins?

A

Products of POMC cleavage

20
Q

What human CNS mutations cause a change in appetite?

A

POMC def and MC4R mutations cause morbid obesity

No NPY/Agrp mutations associated with appetite

21
Q

List the other brain regions that signal to the hypothalamus

A

Higher centres
Amygdala
Other parts of hypothalamus e.g. lateral hypo
Vagus nerve to brainstem to hypothalamus

22
Q

What is the role of the adipostat mechanism?

A

The bodies control and sensitivity to adiposity and thus weight. Signal to control appetite and energy expenditure

23
Q

How does the adipostat mechanism work?

A

Leptin produced by adipocytes in white adipose tissue. Hypothalamus senses the concentration of the hormone and alters neuropeptides to increase/decrease food intake

24
Q

Where does leptin act?

A

Arcuate and ventromedial nuclei to regulate appetite and thermogenesis (energy expenditure) in adipostat mechanism

25
Q

Other than the adipostat mechanism what other roles does leptin have?

A

Development of atherosclerosis via innate immune system

Low levels in Alzheimer’s disease and depression

26
Q

What is congenital leptin deficiency?

A

Lack of leptin causing severe obesity in early life as children are constantly hungry and eating

Exogenous leptin effective in reducing weight
Rare

27
Q

What is the relationship between leptin and obesity?

A

Serum leptin concentrations correlated to percentage body fat suggesting obese individuals become insensitive to endogenous leptin production

Exogenous leptin ineffective as weight control drug

28
Q

What 3 ways can go wrong in leptin’s mechanism of action?

A

Absent leptin e.g. congenital leptin def
Leptin resistance e.g. in obese people
Mutation in leptin/receptor

29
Q

When body fat is high, what is leptin?

A

High and vice versa

Proportional to fat mass

30
Q

What causes us to feel less hungry after a meal?

A

Bulk in stomach
Nutrients in circulation

BUT MOST IMPORTANTLY
Hormones from gut

31
Q

What cells secrete GI hormones?

A

Enteroendocrine cells of stomach, pancreas and small intestine

32
Q

Which two GI hormones regulate appetite?

A

Ghrelin - increase appetite

Peptide YY - reduces appetite

33
Q

How does ghrelin work?

A

Highest levels before meals to help prepare food intake by increasing gastric motility and acid secretion.

Stimulates NPY/Agrp neurones
Inhibits POMC neurones

Increases appetite
Regulates reward, taste sensation, memory and circadian rhythm

34
Q

How does PYY work and where is it secreted?

A

Short peptide secreted in terminal ileum and colon in response to food arriving to TI and colon

Inhibits NPY neurones
Stimulated POMC neurones

Decreases appetite - can be injected as a drug

35
Q

What comorbidities is obesity associated with?

A 
Depression
Stroke
MI
Hypertension
Diabetes - PVD
Gout
Osteoarthritis
Bowel cancer and others
Sleep apnoea

GASTROENTEROLOGY 2 (7 decks)

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