Apetite

Question 1

What are the three factors that regulate thirst?

Answer 1

1) Plasma osmolarity
2) Hypovolaemia
3) Hypotension

Question 2

Where is vasopressin released from?

Answer 2

Herring bodies of the posterior pituitary gland i

Question 3

Which types of neurones release vasopressin?

Answer 3

Magnocellular hypothalamic neurones

Question 4

Which hypothalamic nuclei release vasopressin?

Answer 4

Supraoptic and paraventricular nuclei

Question 5

Which receptors are stimulated by vasopressin?

Answer 5

V2 receptors on tubule cells of the collecting duct and distal convoluted tubule

Question 6

Which types of channels are synthesised in response to vasopressin?

Answer 6

Aquaporin-2 channel expression to increase water permeability and reabsorption

Question 7

What is the effect of low plasma ADH?

Answer 7

Water diuresis

Question 8

What is the effect of high plasma ADH?

Answer 8

Anti-diuresis

Small volume of concentrated urine

Question 9

Where are osmoreceptors found?

Answer 9

Circumventricular residing within the organum vasculosu, and the subfornical organ

Question 10

How do osmoreceptors induce ADH release?

Answer 10

1. Detection of increased plasma osmolarity.
2. Osmoreceptor cell shrinkage (due to water diffusing into extracellular environment).
3. Conformational change increases proportion of cation channels expressed on the cell surface membrane.
4. Increased influx of cations  Membrane depolarisation.
5. Transmits action potentials to ADH producing magnocellular hypothalamic neurones
6. Improved fluid retention

Question 11

What happens to the osmoreceptor when there is an increase in plasma osmolarity?

Answer 11

Cell shrinkage, due to water diffusing into extracellular environment.

Question 12

What happens to the osmoreceptors when there is conformational change?

Answer 12

Causes an increase in the expression of cation channels expressed on the cell surface membrane
-influx of cations, causing membrane depolarisation

Question 13

What effect does ADH do in hypertonic conditions?

Answer 13

increased fluid retention, by stimulating water reabsorption

Question 14

What happens in hypotonic conditions to ADH>

Answer 14

In hypotonic conditions, osmoreceptor cells maintain their structural shape, and cation channels are inhibited  Reduced cation influx induces a state of hyperpolarisation to inhibit firing.

Question 15

Where are thirst receptors located?

Answer 15

Mouth, pharynx, and oesophagus

Question 16

What is the effect of the stimulation of thirst receptors?

Answer 16

They are stimulated by detecting water consumption, and relieve the sensation of thirst in the short-term

Question 17

How is thirst sensation completely satisfied?

Answer 17

• Thirst sensation is completely satisfied once plasma osmolarity is corrected or blood volume/arterial pressure is restored to normal.

Question 18

What is the response to low renal perfusion pressure by JG cells?

Answer 18

Renin is secreted (increased sympathetic activity by stimulating beta-1 receptors).

Question 19

What is the effect of renin?

Answer 19

Converts angiotensinogen into angiotensin-I

Question 20

What is the effect of ACE?

Answer 20

Converts angiotensin-I to angiotensin-II

Question 21

What is the effect of angiotensin-II?

Answer 21

A potent vasoconstriction to increase systemic blood pressure and increases sympathetic activity.

• Promotes thirst
• Promotes ADH secretion
• Promotes aldosterone synthesis
• Increased sodium reabsorption

Question 22

What effect does aldosterone have on tubule cells of the distal convoluted tubule?

Answer 22

Sodium reabsorption

Potassium secretion

Question 23

What is the effect of ACE-inhibitors?

Answer 23

Inhibit the conversion of angiotensin -I to angiotensin-II
reduces vasoconstrictive properties of angiotensin-II
vasodilator

Question 24

What is an ARB?

Answer 24

Angiotensin-receptor blocker

Question 25

Where is aldosterone synthesised?

Answer 25

In the zona glomerulosa of the adrenal cortex

Question 26

What is the mechanism of an ARB?

Answer 26

• Angiotensin-II receptor blockers are receptor antagonists which prevent angiotensin-II from exerting hypertensive effects.

Question 27

What is adipose tissue expansion?

Answer 27

Reduces food intake and increases energy expenditure.

Question 28

What happens to energy expenditure when there is a reduction in fat mass?

Answer 28

Reduction in fat mass - Increased

Question 29

What is the ventromedial nucleus?

Answer 29

Ventromedial nucleus is associated with inducing a state of satiety, a lesion to the ventromedial nuclei increases the sensation to intake food contributing to severe obesity.

Question 30

What is the impact to a lesion to the ventromedial nucleus?

Answer 30

Increases the sensation of food intake - leading to severe obesity

Question 31

What is the role of the ventromedial nucleus?

Answer 31

Induces a state of satiety

Question 32

What type of factor is released from the lateral hypothalamic nucleus?

Answer 32

Releases orexigenic factors

Question 33

What is an orexigenic factor?

Answer 33

Behaves as an appetite stimulant

Question 34

Which structure includes both orixgenic and anorexigenic neurones?

Answer 34

Arcuate nucleus

Question 35

What are orexigenic neurones?

Answer 35

are appetite stimulating – releasing neuropeptide Y and agouti-related peptides. (LHN)

Question 36

Which peptides are released from orexigenic neurones?

Answer 36

Neuropeptide Y and agouti-related peptides (LHN)

Question 37

What are anorexigenic neurones?

Answer 37

POMC/CART neurones are appetite suppressive – releasing MSH. (VHN). These neurones are directly innervated and inhibited by the NPY neurones.

Question 38

Which peptides are released from anorexigenic neurones?

Answer 38

Alpha-MSH

Question 39

What directly inhibits POMC neurones?

Answer 39

NPY neurones

Question 40

Where do the neuronal projections terminate at?

Answer 40

Paraventricular nucleus of the hypothalamus, adjacent to the third ventricle.

Question 41

What does the paraventricular nucleus secrete?

Answer 41

Oxytocin and ADH

Question 42

How does the arcuate nucleus receive hormonal stimulation?

Answer 42

There is an incomplete blood brain barrier - enabling access for the arcuate nucleus to interact with circulating hormones

Question 43

Which hormones inhibit orexigenic neurones?

Answer 43

Leptin, peptide YY, and insulin

Question 44

Which hormone stimulates orexigenic neurones?

Answer 44

Ghrelin

Question 45

What is the hunger reflex?

Answer 45

Hunger: 1. Decreased stimulation of mechanoreceptors within the stomach 2. Decreased firing frequency of the vagal nerve to the solitary nucleus. 3. Solitary nucleus relays information to the arcuate nucleus within the hypothalamus 4. Activates the lateral hypothalamic nucleus via orexigenic factors 5. Supresses the ventromedial nucleus via the anorectic factors.

Question 46

Which nucleus relays information to the arcuate nucleus?

Answer 46

Solitary nucleus

Question 47

Which nucleus is activated during hunger?

Answer 47

Lateral hypothalamic nucleus

Question 48

Which factors are released during hunger from the lateral hypothalamic nucleus?

Answer 48

Orexigenic factors

Question 49

Which centres are suppressed during hunger?

Answer 49

Ventromedial nucleus

Question 50

Which hormone is released during hunger?

Answer 50

Ghrelin - stimulates the arcuate nucleus

Question 51

What effect does leptin have on appetite sensation?

Answer 51

Inhibits appetite sensation (binds to leptin receptors on both NPY and POMC neurones)

Question 52

Which peptide is released from POMC neurones?

Answer 52

POMC neurones of the arcuate nucleus release alpha-MSH peptides which induce an anorexigenic effect

Question 53

What type of effect is exerted by alpha-MSh neurones?

Answer 53

Anorexigenic effect on the paraventricular nucleus

Question 54

What type of receptors does alpha-MSH bind to?

Answer 54

MC-4, triggers the sensation of satiety

Question 55

What happens in an NPY and Agrp mutation?

Answer 55

This is associated with reduced appetite.

Question 56

What is the effect of a POMC deficiency or MC4-R mutation?

Answer 56

Cause obesity given that the induction of satiety is lost

Question 57

Which cells release leptin and circulating hormones?

Answer 57

Adipocytes

Question 58

Which tissue synthesises leptin?

Answer 58

White adipose tissue

Question 59

What is the effect of leptin?

Answer 59

Regulate intake and thermogenesis by inhibiting orexigenic neurones (NPY, AGRP) within the arcuate nucleus and lateral hypothalamic area Stimulates the anorexigenic neurones

Question 60

What is congenital leptin deficiency?

Answer 60

There is a significant reduction in circulating leptin, thus the inhibitory effect on orexigenic neurones is lost - promoting feeding behaviour and intake Manifests as severe early age obesity

Question 61

What is the treatment of congenital leptin deficiency?

Answer 61

Leptin injections can reduce body weight

Question 62

What is the relationship between serum leptin and body fat?

Answer 62

Serum leptin is higher in comparison to baseline patients in obesity, suggesting that hypothalamus is insensitive to endogenous leptin production

Question 63

What is the effect of Ghrelin?

Answer 63

Stimulates appetite and increases gastric emptying * Directly modulates neurones in the arcuate nucleus. Stimulates NPY/Agrp neurones. * Inhibits POMC neurones. * Increases appetite * Regulation of reward, taste sensation memory, circadian rhythm

Question 64

What is the relationship between plasma ghrelin and pre-prandial?

Answer 64

Plasma ghrelin increases twofold pre-prandially Decreases thereafter post-prandially

Question 65

What rhytmn is exhibited by ghrelin inter-prandially?

Answer 65

Diurnal

Question 66

Which cells secrete peptide YY?

Answer 66

Enteroendocrine L cells, throughout the mucosa of the terminal ileum, colon and rectum

Question 67

What is the effect of peptide YY?

Answer 67

Increases post-prandially, to reduce appetite and food intake Inhibits NPY orexigenic release Stimulates POMC anorexigenic releases N.B: Also reduces intestinal motility, gall bladder contractions and inhibits pancreatic exocrine secretion. -Can cause nausea.

Question 68

What comorbidities are associated with obesity?

Answer 68

``` Depression Sleep apnoea Bowel cancer Stroke Osteoarthritis Gout Peripheral vascular disease Diabetes Hypertension MI ```