Appetite

Question 1

What factors can control thirst?

Answer 1

• body fluid osmolality
• reduced blood volume
• reduced blood pressure

Question 2

What is the most potent stimulus of thirst?

Answer 2

plasma osmolality increase more potent stimulus (change of 2 - 3%) induces strong desire to drink

Question 3

Hormone that helps regulate osmolality?

Answer 3

ADH / vasopressin

Question 4

What does ADH act on?

Answer 4

collecting duct aquaporin 2 channel, acts on kidneys to regulate volume and osmolality of urine

Question 5

When plasma ADH is low?

Answer 5

large volume of urine excreted

Question 6

When plasma ADH is high?

Answer 6

small volume of urine excreted

Question 7

Where are osmoreceptors found?

Answer 7

in hypothalamus (organum vasculosum of lamina terminalis (OVLT) and subfornical organ (SFO))

Question 8

How do osmoreceptors lead to ADH release?

Answer 8

1. cells shrink when plasma more conc.
2. higher proportion of cations so membrane depolarizes
3. send signals to ADH producing cells to increase ADH
4. fluid retention, invokes drinking

Question 9

Describe the sensation of thirst?

Answer 9

• sensation decreased by drinking even before sufficient water absorbed by GI tract to correct osmolality
• receptors in mouth, pharynx and oesophagus involved
• relief of thirst sensation by these receptors is short lives
• thirst only completely satisfied once plasma osmolality decreased or blood volume or arterial pressure corrected

Question 10

What cells in the renal afferent arteriole respond to a drop in blood pressure?

Answer 10

juxtaglomerular cells respond by releasing angiotensinogen

Question 11

Where is angiotensinogen converted into angiotensin I?

Answer 11

in the liver

Question 12

How is angiotensin I converted into angiotensin II?

Answer 12

using ACE in the lungs

Question 13

What are some effects of angiotensin II?

Answer 13

• thirst
• acting on zona glomerulosa
• water retention
• ADH secretion
• vasoconstriction, increasing sympathetic activity

Question 14

What stimulus does the zona glomerulosa of the adrenal cortex respond to?

Answer 14

high potassium, low sodium and angiotensin II

Question 15

What does aldosterone and angiotensin II lead to?

Answer 15

water retention via Na+Cl- absorption and K+ excretion

Question 16

Outline body weight homeostasis

Answer 16

reduction in fat mass increases food intake and reduces energy expenditure whilst adipose tissue expansion reduces food intake and increases energy expenditure.

Question 17

What signals act on the hypothalamus to regulate appetite?

Answer 17

• Ghrelin, PYY and other hormones
• neural input from periphery and other brain regions
• leptin

Question 18

What is the role of the arcuate nucleus?

Answer 18

brain area involved in regulation of food intake

Question 19

What kind of barrier does the arcuate nucleus have?

Answer 19

incomplete BBB allowing access to peripheral hormones - integrates peripheral and central feeding signals

Question 20

What are the 2 neuronal populations of the arcuate nucleus?

Answer 20

stimulatory i.e. increases feeding (NPY/Agrp neuron) or inhibitory i.e. decreases feeding (POMC neuron)

Question 21

Which nucleus controls appetite and energy expenditure?

Answer 21

paraventricular nucleus