appetite regulation :

Question 1

when does an individual perceive thirst?

Answer 1

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

Question 2

what is the most potent signal?

Answer 2

Plasma osmolality increased is the more potent stimulus

Question 3

how does ADH act?

Answer 3

Acts on the kidneys to regulate the volume and osmolality of urine

• when ADH is low a large amount of urine is made
• when ADH is high a small amount of urine is made

Question 4

where are osmoreceptors and ADH released from?

Answer 4

• Found in the hypothalamus, OVLT, and SFO

* **

Question 5

what do osmoreceptors do?

Answer 5

• Sense changes in body fluid osmolality
• Cells shrink or swell in response
• ## Send signals to the ADH producing cells in the hypothalamus to alter ADH release.

Question 6

what does increased plasma osmolarity result in?

Answer 6

• Invokes drinking and ADH release

- Increased ADH stimulates kidney to conserve water.

Question 7

what does decreased plasma osmolarity result in?

Answer 7

• Thirst is suppressed and ADH release decreased

- Absence of ADH the kidney excretes more water.

Question 8

what is the sensation of thirst?

Answer 8

• Receptors in mouth, pharynx, oesophagus seem to be involved.
• Relief of thirst sensation via these receptors is short lived

Question 9

how is thirst satisfied?

Answer 9

once plasma osmolality is decreased or blood volume or arterial pressure corrected.

Question 10

how is angiotensin ii involved in sensation of thirst?

Answer 10

• Evokes the sensation of thirst
• angiotensin ii is increased when blood volume and pressure are reduced.
• Activates SFO neurons
• all contributes to homeostasis

Question 11

what is the function of the hypothalamus in terms of body weight ?

Answer 11

• its part of homeostasis

- the hypothalamus decides the food intake you need and the energy expenditure

Question 12

why are there so many different hormones that make you hungry or full?

Answer 12

• different reasons for being hungry result in different hunger
  eg. being hungry for 2 hours compared to being hungry for 2 years

Question 13

what is the hypothalamus made out of?

Answer 13

LATERAL HYPO
PARAVENTRICULAR NUCLEUS
VENTROMEDIAL HYPO

Question 14

what is the arcuate nucleus?

Answer 14

• brain area involved in the regulation of food intake.
• Incomplete blood brain barrier, allows access to peripheral hormones
• Integrates peripheral and central feeding signals.

Question 15

what are the two neural populations?

Answer 15

Stimulatory (NPY/Agrp neuron)

Inhibitory (POMC neuron)

Question 16

how does the melanocortin system work?

Answer 16

• exists in the para ventricular nucleus and when stimulates decreases the food intake
• So POMC stimulates MC4R to REDUCE feeding.
• POMC is broken down to a-MSH which acts on MC4R.

Question 17

what mutations might affect appetite?

Answer 17

• POMC deficiency and MC4R mutations cause MORBID OBESITY.

- as there is no limit on food intake

Question 18

what are other signals from other brain regions?

Answer 18

Amygdala- emotion, memory

Vagus to brain stem to hypothalamus.

Question 19

how does the adipostat mechanism work?

Answer 19

• Circulating hormone produced by fat
• Hypothalamus senses the concentration of hormone.
• Hypothalamus then alters neuropeptides to increase or decrease food intake.

Question 20

what is leptin made by?
where does it circulate?
what does it do?

Answer 20

Made by adipocytes in white adipose tissue.
circulates in plasma

Acts upon the hypothalamus regulating appetite (intake) and thermogenesis (expenditure).

Question 21

what are leptin levels depending on body fat?

Answer 21

• low for low body fat

- high when high body fat

Question 22

what happens when you are obese?

Answer 22

people who are obese have high leptin but the leptin receptors are resistant to it

Question 23

for kids with a missing leptin gene who are fat what happens?

Answer 23

injecting leptin can cause loss of weight

Question 24

why do we feel less hungry after we have eaten a meal?

Answer 24

• hormones released from the gut are very important

- ghrelin and PYY

Question 25

how does PYY directly modulate neurones?

Answer 25

• Inhibits NPY release.
• Stimulates POMC neurons
• Decreases appetite.

PYY is secreted post-prandial and the levels secreted are
proportional the the amount of calories in the meal.

Question 26

how does ghrelin reduce appetite?

Answer 26

• Ghrelin drives hunger before a meal and then drops after consumption
• Stimulates NPY/Agrp neurones.
• Inhibits POMC.
• increases food intake

Question 27

compare ghrelin and PYY?

Answer 27

• they do the opposite to eachother

Question 28

what are some of the obesity epidemic theories?

Answer 28

• Thrifty Gene Hypothesis:
  thin people dont survive famines so they dont pass on their genes
• Adaptive Drift Hypothesis –
  Humans used to be eaten by wild animals. In this time, fat people were eaten and the thin starved, giving a
  normal distribution of weight.
• We then learnt to defend ourselves against these animals so the fat people were not eaten but the thin still
  starved.