appetite & disorders

Question 1

what is the strongest stimulus for thirst

Answer 1

plasma osmolarity

over blood volume/arterial pressure

Question 2

action of vasopressin

Answer 2

regulates volume and osmolarity of urine
via aquaporin 2 channels on collecting duct
more adh = small amount of urine (less water)

Question 3

where are the osmoreceptors?

Answer 3

organum vasculosum of lamina terminalis
subfornical organ
within hypothalamus

Question 4

stimulus of thirst?

Answer 4

cells shrink via osmosis if plasma is more concentrated (no BBB)
proportion of cation channels increases - membrane depolarises
sends signals to ADH producing cells for ADH release
fluid retention and invokes drinking

Question 5

how is the sensation of thirst satiated?

Answer 5

decreased by drinking (before sufficient water has yet been absorbed to correct osmolarity)
receptors in mouth, pharynx and oesophagus
but SHORT LIVED release - only completely satiated when plasma osmolarity decreased/blood volume/arterial pressure

Question 6

how is a reduction in blood pressure regulated by the body, starting in the kidney

Answer 6

fall in bp detected by juxtaglomerular cells in renal afferent arteriole
renin produced
angiotensinogen converted to angiotensin I in liver
angiotensin I- II in lungs by ACE
results in vasoconstriction, thirst, stimulation of aldosterone secretion in zona glomerulosa, H2O retention and Na retention, ADH secretion

Question 7

where in the brain is responsible for appetite

Answer 7

hypothalamus:
arcuate nucleus
lateral hypothalamus (feeding centre)
ventromedial hypothalamus (satiety centre)

Question 8

what is the arcuate nucleus

Answer 8

brain area involved with regulation of food intake (via lateral and ventromedial hypothalamus)
with 2 neuron groups: neuropeptide Y/agouti-related peptide and POMC

Question 9

how is appetite regulated by the hypothalamus

Answer 9

stimuli - insulin and leptin (levels of circulating factors)ghrelin, vagus nerve stimulation of AN

arcuate nucleus - orexigenic and anorectic neurons send signals to inhibit/stimulate:

paraventricular nucleus - ADH

lateral hypothalamus - orexigenic peptides (feeding centre)

ventromedial hypothalamus - anorexigenic peptides /melanocortins (satiety centre)

Question 10

where is the arcuate nucleus

Answer 10

medial-basal part of hypothalamus, adjacent to 3rd ventricle

Question 11

what is the paraventricular nucleus

Answer 11

collection of neurons around 3rd ventricle in hypothalamus
controls energy expenditure and appetite
produces ADH and oxytocin
terminal field of arcuate nucleus neurons (appetite neurons)

Question 12

what mechanisms of weight homeostasis kick in if weight reduces

Answer 12

reduced sympathetic activity
reduced energy expenditure
reduced thyroid activity
increased hunger/food intake

Question 13

what weight homeostasis mechanisms kick in when weight is increased?

Answer 13

increased sympathetic activity
increased energy expenditure
reduced hunger/food intake

Question 14

how does peripheral input for appetite reach the brain (not through blood)

Answer 14

vagus nerve

Question 15

what are the orexigenic neurons

Answer 15

neuropeptide Y and AGRP neurons

Question 16

what are the anorexic neurons

Answer 16

POMC neurons

Question 17

how do melanocortins produce their effect

Answer 17

alpha-MSH (melanocyte stimulating hormone) released by POMC neurons in arcuate nucleus
binds to MC4R in paraventricular nucleus
this decreases appetite and suppresses food intake

Question 18

how does the arcuate nucleus know to increase appetite?

Answer 18

receptors for insulin and leptin

decrease of either will stimulate NPY/AGRP neurons to increase appetite

Question 19

what is leptin

Answer 19

anorexigenic hormone made by adipocytes
proportional to body fat
inhibits NPY and AGRP, stimulates POMC neurons

Question 20

what is ghrelin

Answer 20

orexigenic gut hormone from enteroendocrine cells

increase before every meal

Question 21

how does ghrelin work for appetite

Answer 21

stimulates NPY/AGRP neurons
inhibits POMC neurons
increases gastric motility and secretions
displays a diurnal rhythm

Question 22

what is peptide YY

Answer 22

anorexigenic gut hormone produced by terminal ileum and colon
suppresses appetite
inhibits NPY, stimulates POMC

Question 23

how does peptide YY work for appetite

Answer 23

inhibits NPY neurons
stimulates POMC neurons
suppresses appetite

Question 24

what gene mutations are associated with obesity?

Answer 24

POMC neuron mutations

Question 25

what hormone is related to obesity

Answer 25

lepin resistance

Question 26

what is secondary polydipsia

Answer 26

due to a medical issue disruptinf any step in osmoregulation or alter ADH

Question 27

causes of secondary polydipsia

Answer 27

``` diabetes I and M kidney failure conns syndrome addisons disease sickle cell diuretics and laxatives antidepressants dehydration ```

Question 28

name some causes of dehydration

Answer 28

``` sweating acute illness fevers vomiting diarrhoea underhydration ```

Question 29

causes of primary polydipsia

Answer 29

its mentaw iwwness innit brain injuries organic brain damage

Question 30

what issues may be caused by polydipsia

Answer 30

``` hyponatraemia causing: kidney/bone damage headaches nausea/cramps slowed reflexes/slurred speech low energy confusion/seizures ```

Question 31

what is adipsia

Answer 31

absence of thirst

Question 32

categories of anorexia nervosa

Answer 32

mild - BMI >17 moderate 16-16.99 severe - 15-15.99 extreme <15

Question 33

signs of anorexia nervosa

Answer 33

``` low BMI continuous weight loss amenorrhoea halitosis mood swings dry hair/skin/ thinning ```

Question 34

causes of anorexia nervosa

Answer 34

genetic environmental psychological sociological

Question 35

what is an eating disorder

Answer 35

mental illness characterised by altered eating habits

Question 36

what is the mechanism behind anorexia

Answer 36

serotonin

Question 37

what is the treatment of obesity?

Answer 37

best results - diet and exercise | bariatric surgery if severe

Question 38

when is bariatric surgery offered to an obese individual

Answer 38

BMI 40+ OR 35+ Comorbidities

Question 39

most common bariatric surgery

Answer 39

roux-en Y gastric bypass | 2nd most - sleeve gastrectomy

Question 40

what are the hormonal changes after bariatric surgery

Answer 40

ghrelin reduced | Glucagon-like peptide 1&2, PYY elevated

Question 41

role of lateral hypothalamus in appetite

Answer 41

produce only orexigenic (appetite) peptides

Question 42

role of ventromedial hypothalamus in appetite

Answer 42

produce anorexigenic peptides only

Question 43

types of appetite stimuli

Answer 43

``` ghrelin - orexigenic PYY - anorexigenic vagus nerve - mechanoreceptors in stomach (increased firing = anorexigenic) leptin - adipose tissue anorexigenic insulin - anorexigenic ```

Question 44

mechanisms of leptin dysfunction

Answer 44

not enough produced receptor signalling defective decreased sensitivity to leptin

Question 45

levels of leptin depend on

Answer 45

levels of body fat - doesnt fluctuate much during day | high fat = high leptin

Question 46

what is congenital leptin deficiency

Answer 46

constant hunger as a result of no leptin circulating body | leptin effective when replaced in body - body weight reduced