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Gatsro 2 > Appetite > Flashcards

Appetite Flashcards

1
Q

What are the three main triggers through which the body controls thirst?

A
  • Body fluid osmolality
  • Blood volume is reduced
  • Blood pressure is reduced
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2
Q

Which thirst trigger has the most potent stimulus?

A

Plasma osmolality- an change of 2-3% induces a strong desire to drink

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3
Q

How does the body regulate osmolality?

A

Using ADH (vasopressin)

  • It acts on kidneys in the collecting duct through the aquaporin 2 channel to regulate the volume and osmolality of urine
  • When plasma ADH is low a large volume of urine is excreted → called water diuresis
  • When plasma ADH is high a small volume of urine is excreted → called anti diuresis
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4
Q

Where is ADH stored?

A

Posterior pituitary

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5
Q

How does the body detect changes in osmolality?

A

Through osmoreceptors, which are sensory receptors

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6
Q

Where are osmoreceptors found?

A

In the hypothalamus

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7
Q

Which 2 regions are the osmoreceptors found in in the hypothalamus?

A
  • Organum vasculosum of the lamina terminalis (OVLT)
  • Subfornical organ (SFO)
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8
Q

How do osmoreceptors respond when the plasma is hypertonic?

A

1) Under normal conditions, a set proportion of cation channels in osmoreceptor cells are active

2) Under hypertonic (more concentrated plasma) stimulation, the cell shrinks

3) This increases proportion of active cation channels- results in increasing positive charge influx which depolarises membrane

4) This sends signals to the ADH producing cells to increase ADH

5) Leads to fluid retention and invokes drinking

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9
Q

How do the osmoreceptors respond when plasma is hypotonic?

A
  • Cation channels are inhibited
  • Loss of cation influx causes hyperpolarisation and inhibits neuronal firing
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10
Q

Describe the RAAS

A

This is the less effective way of controlling thirst

  • When bp drops, JG apparatus secretes renin
  • Renin is aka angiotensinogenase, an enzyme, and cleaves angiotensinogen secreted by liver to activate it to become angiotensin I
  • Angiotensin I then converted into angiotensin II by ACE which happens in lungs
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11
Q

Describe the effects of angiotensin II?

A

-Induces thirst
-Leads to aldosterone release from the zona glomerulosa
-Aldosterone retains water through Na+Cl absorption and K+ secretion

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12
Q

What 2 important types of drugs are important in this system?

A
  • Direct renin inhibitors
  • ACE inhibitors
  • Both used to treat bp
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13
Q

What does the body do if fat mass is reduced?

A

Try to gain weight by
- Sympathetic NS energy activity decreases
- Energy expenditure decreases
- Hunger/food intake increases
- Thyroid activity decreased

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14
Q

What does the body do if fat mass is increased?

A

Try to decrease weight by:

  • Increasing sympathetic nervous system activity
  • Increasing energy expenditure
  • Decreasing hunger/food intake
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15
Q

Where does appetite regulation occur?

A

Hypothalamus

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16
Q

What peripheral stimuli are there that are involved in appetite regulation?

A
  • Ghrelin, PYY and other gut hormones- communicate through vagus nerve to brainstem which communicates with hypothalamus which then communicated with higher CNS regions like amygdala
  • Neural input from the periphery and other brain regions
  • Leptin (via leptin control system)
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17
Q

How does the hypothalamus sensitize a response?

A

By increasing or decreasing energy expenditure and food intake.

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18
Q

What is the arcuate nucleus responsible for?

A
  • It’s an aggregation of neurones in the medial basal part of the hypothalamus and is adjacent to the 3rd ventricle
  • It has:
    • orexigenic (appetite stimulating/increasing) neurones
    • anorectic (appetite suppressive) neurones
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19
Q

When does the arcuate nucleus decrease food intake?

A

When its pro-opiomelanocortin (POMC) neurones activate.

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20
Q

What does the paraventricular nucleus do?

A
  • Lays adjacent to 3rd ventricle
  • Contains neurones that project to posterior pituitary and secrete oxytocin and ADH, to regulate osmoregulation, appetite and stress reaction of the body
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21
Q

What does the lateral hypothalamus do?

A

Produces only orexigenic peptides

22
Q

What does the ventromedial hypothalamus do?

A
  • Associated with satiety
  • Lesions in this region in rats leads to severe obesity
23
Q

What other hypothalamic factors are implicated in appetite regulation?

A
  • Endocannabinoids
  • AMP (activated protein kinase)
  • Protein tyrosine phosphatase
24
Q

Arcuate nucleus - What does it do?

A
  • Brain area involved in regulation of food intake
  • Integrates peripheral and central feeding signals
25
Q

What is the arcuates BBB like and why?

A

Incomplete BBB to allow access to peripheral hormones

26
Q

What 2 neuronal populations does the arcuate nucleus have?

A

-Stimulatory neurones
-Inhibitory neurones

27
Q

Stimulatory neurones- what peptide do they produce?

A
  • neuropeptide Y (NPY)
  • Agouti-related peptide (Agrp)
28
Q

Inhibitory neurones- what peptide do they produce?

A

POMC

29
Q

What receptors for two other hormones does the arcuate nucleus have?

A

For leptin and insulin, activated by a decrease or increase of leptin or insulin signalling.

30
Q

What kinds of conditions lead to increased food intake through this mechanism?

A
  • Fasting
  • Uncontrolled diabetes
  • General leptin deficiency
31
Q

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

A
  • Cross incomplete BBB and penetrate arcuate nucleus
  • Either POMC neurones or NPY/Agrp neurones are activated which both go to the paraventricular nucleus
32
Q

Besides feeding, what other 2 important things is the arcuate nucleus involved in?

A

-Fertility regulation
-Cardiovascular regulation

33
Q

How does the melanocortin system work?

A
  • Melanocortin 4 receptors are expressed on paraventricular nucleus.
  • Agrp neurones release Agrp which act on MC4R as antagonists.
  • POMC neurones produce melanocortins, classic example is alpha-MSH, which act on MC4R as agonists → leads to decrease in appetite and weight along with food intake.
34
Q

What can POMC deficiency cause?

A

Morbid obesity

35
Q

What can MC4R mutations cause?

A

Morbid obesity

36
Q

What is the adipostat mechanism?

A

The body’s thermostat i.e. control of energy expenditure through thermoregulation (controlling body temp) which keeps individual’s fat mass within narrow range despite changes to diet or daily activity

37
Q

How does adipose tissue interact with hypothalamus for it to regulate food intake?

A
  • Circulating hormones are produced by adipose tissue- the more adipose tissue, the more hormones being produced
  • Hypothalamus senses conc of hormones then alters neuropeptides to increase or decrease food intake
38
Q

Which hormone regulates appetite and thermogenesis?

A

Leptin

39
Q

What produces leptin?

A

White adipose tissue and enterocytes.

40
Q

Where does leptin act?

A

Acts upon cell receptors in the arcuate and ventromedial nuclei

41
Q

Where are the arcuate and ventromedial nuclei found?

A

Arcuate nuclei- base of the hypothalamus

Ventromedial nuclei- middle of the hypothalamus

42
Q

What are leptin levels like in obese patients and what does this suggest?

A

Serum leptin higher, suggests obese people are resistant to endogenous leptin production.

43
Q

What are the 3 mechanisms through which the physiological effect of leptin may not work?

A
  • There is insufficient production of leptin
  • There is a defect in the regulatory signalling and reduced leptin levels despite high adipose tissue mass
  • There is a decreased sensitivity to leptin (similar to insulin resistance in T2DM)- this results in inability to detect satiety despite high energy stores and leptin levels
44
Q

Why do we feel full after a meal?

A

Hormone signals from the gut.

45
Q

What secretes GI hormones?

A

Enteroendocrine cells in the stomach, pancreas and small bowel.

46
Q

What is ghrelin?

A

Helps prep for food intake by increasing gastric motility and acid secretion.
Returns to lower levels after meal times.

47
Q

What is ghrelin also known as?

A

Hunger hormone

48
Q

How does ghrelin work in the hypothalamus?

A

Direcetly modulates neurones in the arcuate nucleus
- Stimulates NPY/Agrp neurones
- Inhibits POMC neurons

49
Q

When are POMC neurons activated.

A

When there is high blood sugar, leptin levels (post eating)

50
Q

What is peptide tyrosine tyrosine, where is it released from and what does it do?

A

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

-Reduces appetite by inhibiting NPY release and stimulating POMC neurons

51
Q

What causes PYY release?

A

Food arriving in the terminal ileum/colon.

Gatsro 2 (8 decks)

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