Appetite Flashcards
What factors determine when we get thirsty?
Body fluid osmolality
Blood volume is reduced
Blood pressure is reduced
Q. Which is the most potent stimulus?
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
What regulates osmolality and where does it work?
Antidiuretic hormone (ADH) or vasopressin
Acts on the kidneys to regulate the volume & osmolality of urine
—-Collecting duct - Aquaporin 2 channel
What happens when plasma ADH is low?
A large volume of urine is excreted (water diuresis)
What happens when plasma ADH is high?
a small volume of urine is excreted (anti diuresis)
Where is ADH stored?
posterior pituitary
What are osmoreceptors? What is their function? Where are they found?
Sensory receptors
Osmoregulation
Found in the hypothalamus
Which regions are these receptors found in the hypothalamus?
Organum vasculosum of the lamina terminalis (OVLT)
Subfornical Organ (SFO)
How do osmoreceptors work to release ADH>
How is thirst decreased? What receptors are involved? How is thirst completely satisfied?
-Thirst is decreased by drinking even before sufficient water has been absorbed by the GI tract to correct plasma osmolality
-Receptors in mouth, pharynx, oesophagus are involved
-Relief of thirst sensation via these receptors is short lived
-Thirst is only completely satisfied once plasma osmolality is decreased or blood volume or arterial pressure corrected.
What are changes in blood pressure and volume controlled by?
The renin-angiotensin-aldosterone system
How does the renin-angiotensin-aldosterone system work?
What does a reduction in fat mass increase?
Food intake and reduces energy expenditure
What does adipose tissue expansion reduce?
Food intake and increases energy expenditure
What happens in overfed state during weight homeostasis?
What happens in underfed state during weight homeostasis?
What information does the hypothalamus take in during appetite regulation?
What does the hypothalamus control in appetite regulation?
-Food intake
-Energy expenditure
What is the appetite stimulating peptide?
Orexigenic
What is the appetite suppressive peptide?
Anorectic
What is the arcuate nucleus’s function?
Synthesises information leading to the production of orexigenic and anorectic neuropeptides
Where is the arcuate nucleus?
Basal medial aspect of hypothalamus
Surrounding third ventricle
Where does the arcuate nucleus pass information to?
Paraventricular nucleus and this has neurones that terminate in the posterior pituitary
What does the lateral hypothalamus do?
Produces orexigenic neuropeptides
What do AGRP neurones do?
Inhibits POMC
What mutation can cause morbid obestiy?
POMC deficiency and MC4-R mutations cause morbid obesity.
What is involved in the melanocortin system?
What other brain regions send signals that are involved in appeitite?
Explain the Adipostat mechanism
Where is leptin made and where is it circulating?
Where does it act and what does it do?
Made by adipocytes in white adipose tissue and enterocytes
Circulates in plasma.
Acts upon the hypothalamus regulating appetite (intake) and thermogenesis (expenditure).
Explain the systemic effect of leptin?
Low when low body fat
High when high body fat
Replacement in the ob/ob mouse decreases weight
Hormone that decreases food intake and increases thermogenesis
Explain leptin resistance
Leptin circulates in plasma in concentrations proportional to fat mass
Fat humans have high leptin
Obesity due to leptin resistance- hormone is present but doesn’t signal effectively
Leptin is ineffective as a weight control drug.
Explain the mechanism of leptin
Why do we feel less hungry after a meal?
Hormonal Signal from the gut
Where are gastrointestinal hormones secreted from?
What are their functions?
Enteroendocrine cells in the stomach, pancreas & small bladder
Control various functions of digestive organs
What does Ghrelin do?
Stimulate appetite, increases gastric emptying
What does Peptide YY do?
Inhibits food uptake
When is Ghrelin highest?
What does it do?
What neurones does it modulate?
Why is PYY not a successful weight loss medication?
As the consequences are intolerable - nausea and vomitting
What is PYY?
Where is it released?
What are the consequences of obesity?
Depression
Sleep apnoea
Bowel cancer
Osteoarthritis
Gout
Stroke
Myocardial infarction
Hypertension
Diabetes
Peripheral vascular disease
