Appetite regulation

Question 1

What triggers thirst perception?

Answer 1

increase fluid osmolarity
reduced blood volume
BP reduced

small changes in plasma osmolarity more potent stimulus

Question 2

Where are osmoreceptors located?

Answer 2

hypothalamus
OVLT - organum vasculosum
SFO - subfornical organ

both are circumventricular organs not completely protected by blood brain barrier (allow sensing of circulation)

Question 3

What is the function of osmoreceptors?

Answer 3

sense changes in fluid osmolality
send signals to ADH producing cells in hypothalamus to alter ADH
also trigger thirst sensation in CNS

increase osmolality - drink, ADH release

Question 4

Removal of final correction of thirst?

Answer 4

need to correct plasma osmolality

thirst is initially decreased by drinking before sufficient water absorbed by GI tract

Question 5

What is the function of angiotensin II in terms of plasma osmolality?

Answer 5

triggers thirst
when plasma osmolality high
Ang2 reduced and SFO neurones stimulated to restore normal body fluid levels

Question 6

What releases renin?

Answer 6

juxtaglomerular cells of renal afferent arteriole

Question 7

How does the hypothalamus regulate body weight?

Answer 7

integrate neural input from periphery and other brain regions, leptin, ghrelin, PYY

result in differences in food intake/energy expenditure

Question 8

Why complex system of hunger regulation?

Answer 8

redundancy in case part of system fails

Question 9

What is the arcuate nucleus function?

Answer 9

circumventricular organ - can access peripheral hormones
regulates food intake
integrate peripheral and central feeling signals

two neuronal populations
stimulatory (NPY, Agrp)
Inhibitory (POMC)

Question 10

How does it work?

Answer 10

circulating factors enter arcuate nucleus

cells bodies and receptors of neurones found in arcuate nucleus
axons extend to paraventricular nucleus or to different parts of brain to influence appetite/food intake /TRH- metabolism

NPY/Agrp increase feeding
POMC decrease feeding
both via PV nucelus

Question 11

What is MC4R?

Answer 11

melanocortin 4 receptor
stimulation inhibits food intake

Agrp is an endogenous antagonist of MC4R –> feel hungry

POMC –> a-MSH

Question 12

What is the effect of POMC and MC4-R mutations?

Answer 12

people typically morbidly obese

POMC –> lose control of ACTH
MC4R –> red hair, obese so no restraint on food intake

Question 13

What else can influence appetite aside from arcuate nucleus?

Answer 13

higher centres
amygdala (emotion, memory)
lateral hypothalamus
brain stem

Question 14

What is the adipostat mechanism?

Answer 14

circulating hormone produced by fat

hypothalamus sense [] of hormone and alter neuropeptides to adjust food intake

Question 15

What is leptin?

Answer 15

made by adipocytes in white adipose tissue
circulates in plasma
acts on hypothalamus to regulate appetite and thermogenesis

• low when low body fat
• replacement decreases weight, increase thermogenesis and decrease food intake

Question 16

What is leptin resistance?

Answer 16

fat people have high lpetin

obesity is due to high resistance as hormone is present but doesnt signal effectively

Question 17

When can leptin be a useful treatment?

Answer 17

those with congenital leptin deficiency
mutation in ob gene
severely hyperphagic and obese

leptin effective in reducing body weight

Question 18

Why do you feel less hungry after a meal?

Answer 18

changes in hormone levels that signal to the brain
- PYY (satiety)
36 AA chain
(PYY3-36 makes you full after a meal after cleave first 2 AAs)

• Ghrelin (hunger)

Question 19

How does PYY modulate neurones in arcuate nucleus?

Answer 19

inhibit NPY release
stimulate POMC release
decrease appetite
raised for some time

Question 20

How does ghrelin directly modulate neurones in arcuate nucleus?

Answer 20

FA attached on Ser3 which affects how it travels in circulation

stimulate NPY/Agrp neurons
inhibit POMC
increase appetite

Question 21

What are consequences of obesity?

Answer 21

depression
sleep apnoea
bowel cancer
osteoarthritis
gout
stroke/MI
hypertension
diabetes
peripheral vascular disease