Appetite

Question 1

What 3 factors stimulate thrist?

Answer 1

• Body fluid osmolality is increased
• Blood volume is reduced
• Blood pressure is reduced

• Plasma osmolality increase is the more potent stimulus – change of 2-3% induces strong desire to drink
• Decrease of 10-15% in blood volume or arterial pressure is required to produce the same response

Question 2

How is thirst decreased?

Answer 2

Drinking

Receptors in mouth, pharynx, oesophagus are involved

Question 3

Thirst is decreased by drinking even before sufficient water has been absorbed by the GI tract to correct plasma osmolality and relief of thirst sensation via these receptors (in mouth, pharynx and oesophagus) is short lived. When is thirst completely satisfied?

Answer 3

• Once plasma osmolality is decreased or blood volume or arterial pressure corrected

Question 4

What happens when there is an increase in osmolarity (6 steps)?

Answer 4

1. Osmoreceptor cells shrink when plasma is more concentrated
2. Proportion of cation channels increase - membrane depolarises
3. Send signal to the ADH producing cells to increase ADH
4. Antidiuretic hormone (ADH) / Arginine vasopressin (AVP) / Vasopressin acts on the kidneys to regulate the volume & osmolarity of urine
5. Increase in ADH causes a decrease in urine and an increase in urine osmolarity
6. Fluid retention causes drinking

Question 5

What are osmoreceptors?

Answer 5

Sensory receptors

Question 6

Where are osmoreceptors found withing the hypothalamus (2)?

Answer 6

• Organ vasculosum of the lamina terminalis (OVLT)
• Subformical organ (SFO)

Question 7

Where does ADH act?

Answer 7

• Aquaporin 2 channel in the collecting duct

Question 8

What happens when there is a decrease in blood pressure (6 steps)?

Answer 8

1. Decrease in BP causes the juxtaglomerular cells of renal afferent arteriole to release renin
2. Renin is converted to Angiotensin I (ca. Angiotensinogen) in the liver
3. Renin is Angiotensin I to Angiotensin II (ca. ACE) in the lungs
4. Angiotensin II causes: Thirst / Vasoconstriction, increase sympathetic activity / ADH secretion
5. Angiotensin II causes the zona glomerulosa of adrenal cortex to release aldosterone
6. Aldosterone causes H₂O retention via Na⁺CL^- absorption and K⁺ excretion

Question 9

What happens when there is a reduction in fat mass (4)?

Answer 9

• Increased in food intake / hunger
• Decreased energy expenditure
• Decreased thyroid function
• Decreased SNS activity

To encourage weight regain

Question 10

What happens when there is an increase in adipose tissue (3)?

Answer 10

• Decreased in food intake / hunger
• Increased energy expenditure
• Increased SNS activity

To encourage weight loss

Question 11

What factors influence food intake & energy expenditure (4)?

Answer 11

• Gherlin, PYY & other gut hormones
• Neural input from the periphery and other brain regions
• Leptin

Question 12

Define orexigenic.

Answer 12

Appetite stimulant

Question 13

Define anorectic.

Answer 13

Appetite suppressive

Question 14

Name this structure in the hypothalamus.

Answer 14

Lateral hypothalamus

Question 15

What is produced by the lateral hypothalamus?

Answer 15

Orexigenic peptides

Question 16

Name this structure in the hypothalamus.

Answer 16

Ventromedial hypothalamus

Question 17

What is the ventromedial hypothalamus associated with?

Answer 17

Feelings of Satiety and Hunger

Question 18

Name this structure in the hypothalamus.

Answer 18

3^rd Ventricle

Question 19

Name this structure in the hypothalamus.

Answer 19

Paraventricular nucleus

Question 20

What is the function of the paraventricular nucleus?

Answer 20

• Contains nurones that project to the posterior pituitary to stimulate the release of ADH & oxytocin

Question 21

Name this structure in the hypothalamus.

Answer 21

Arcuate nucleus

Question 22

What is the arcuate nucleus?

Answer 22

• An aggregation of neuorones in the medial basal part
• Produces both orexigenic and anorexic factors

Question 23

What are the orexigenic factors released by the arcuate nucleus (2)?

Answer 23

• Neuropeptide Y (NPY)
• Agouti-related peptide (AgRP)

Question 24

What are the anorexic factors released by the arcuate nucleus (2)?

Answer 24

• Proopiomelanocortin (POMC)
• Cocaine- and amphetamine-regulated transcript (CART)

Question 25

What regions of the brain (outside the hypothalamus) influence food intake and energy expenditure (2)?

Answer 25

* **Amygdala** - emotion, memory * **Vagus nerve** to brain stem to hypothalamus

Question 26

What peripheral factors influence food intake and energy expenditure (5)?

Answer 26

* Leptin * Adipostat * Ghrelin * Peptide YY (PYY) * GLP1 & GLP2

Question 27

Where is leptin produced?

Answer 27

* Made by **adipocytes** in white **adipose tissue** and enterocytes ## Footnote Leptin concentration is positively correalated with body fat

Question 28

Where is leptin found?

Answer 28

Circulates in plasma

Question 29

What is the effect of increased leptin?

Answer 29

1. **Increased leptin** 2. **Decreased NPY / AgPR** in the arcuate nucleus 3. Decreased AgPR in arcuate nucleus 4. **Decreased food intake / Increased energy** expenditure through the Melanocortin 4 Receptor (MC4R) AND 1. **Increased leptin** 2. **Decreased Melanin-concentrating hormone (MCH) / Orexins** in the lateral hypothalamus 3. **Decreased food intake / Increased energy expenditure** through the Melanocortin 4 Receptor (MC4R)

Question 30

What is leptin resistance?

Answer 30

* **POMC deficiency** & **MC4R mutations** cause morbid obesity ## Footnote No NPY / AgPR mutations associated with appetite disorders in humans

Question 31

Where is adipostat produced?

Answer 31

Adipose tissue

Question 32

Where is adipostat found?

Answer 32

Circulating in the blood

Question 33

What is the function of adipostat?

Answer 33

Acts like a (complicated) **thermostat**: * Hypothalamus senses the concentration of hormone * Hypothalamus alters neuropeptides to increase or decrease food intake

Question 34

What does ghrelin regulate (4)? ## Footnote Gherlin is a gastrointestinal hormone Gastrointestinal hormone: Secreted by enteroendocrine cells in the stomach, pancreas & SB

Answer 34

* Regulation of **reward**, **taste sensation**, **memory** & **circadian rhythm**

Question 35

What is the function of gherlin? ## Footnote Gherlin is a gastrointestinal hormone * Gastrointestinal hormone: Secreted by enteroendocrine cells in the stomach, pancreas & SB

Answer 35

* **Stimulates NPY / AgPR neurones** * **Inhibits POMC / CART neurones** ## Footnote Increase appetite

Question 36

When are gherlin levels the highest?

Answer 36

* **Before meals:** help prepare for food intake by increasing gastric motility and acid secretion

Question 37

Where is peptide YY (PYY) released and in what response?

Answer 37

* Short pepdite released in the **terminal ileum (TI) & colon** in response to **feeding**

Question 38

What is the function of peptide YY (PYY) (4 steps)?

Answer 38

1. **Food at terminal ileum & colon** 1. **PYY released** 1. **Inhibits NPY release & stimulate POMC neurones** 1. **Decrease appetite**

Question 39

What is the function of GLP1 & GLP2 (2)?

Answer 39

* **Stimulate insulin** release * **Inhibit glucagon** release

Question 40

What comorbidities are associated with obesity (10)?

Answer 40

* Depression * Sleep apnoea * Bowel cancer * Osteoarthritis * Gout * Stroke * Myocardial Infarction * Hypertension * Diabetes * Peripheral vascular disease