Appetite Flashcards
What 3 factors stimulate thrist?
- Body fluid osmolality is increased
- Blood volume is reduced
- Blood pressure is reduced
- 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
How is thirst decreased?
Drinking
Receptors in mouth, pharynx, oesophagus are involved
Thirst is decreased by drinking even before sufficient water has been absorbed by the GI tract to correct plasma osmolality and relief of thirst sensation via these receptors (in mouth, pharynx and oesophagus) is short lived. When is thirst completely satisfied?
- Once plasma osmolality is decreased or blood volume or arterial pressure corrected
What happens when there is an increase in osmolarity (6 steps)?
- Osmoreceptor cells shrink when plasma is more concentrated
- Proportion of cation channels increase - membrane depolarises
- Send signal to the ADH producing cells to increase ADH
- Antidiuretic hormone (ADH) / Arginine vasopressin (AVP) / Vasopressin acts on the kidneys to regulate the volume & osmolarity of urine
- Increase in ADH causes a decrease in urine and an increase in urine osmolarity
- Fluid retention causes drinking
What are osmoreceptors?
Sensory receptors
Where are osmoreceptors found withing the hypothalamus (2)?
- Organ vasculosum of the lamina terminalis (OVLT)
- Subformical organ (SFO)
Where does ADH act?
- Aquaporin 2 channel in the collecting duct
What happens when there is a decrease in blood pressure (6 steps)?
- Decrease in BP causes the juxtaglomerular cells of renal afferent arteriole to release renin
- Renin is converted to Angiotensin I (ca. Angiotensinogen) in the liver
- Renin is Angiotensin I to Angiotensin II (ca. ACE) in the lungs
- Angiotensin II causes: Thirst / Vasoconstriction, increase sympathetic activity / ADH secretion
- Angiotensin II causes the zona glomerulosa of adrenal cortex to release aldosterone
- Aldosterone causes H2O retention via Na+CL- absorption and K+ excretion
What happens when there is a reduction in fat mass (4)?
- Increased in food intake / hunger
- Decreased energy expenditure
- Decreased thyroid function
- Decreased SNS activity
To encourage weight regain
What happens when there is an increase in adipose tissue (3)?
- Decreased in food intake / hunger
- Increased energy expenditure
- Increased SNS activity
To encourage weight loss
What factors influence food intake & energy expenditure (4)?
- Gherlin, PYY & other gut hormones
- Neural input from the periphery and other brain regions
- Leptin
Define orexigenic.
Appetite stimulant
Define anorectic.
Appetite suppressive
Name this structure in the hypothalamus.
Lateral hypothalamus
What is produced by the lateral hypothalamus?
Orexigenic peptides
Name this structure in the hypothalamus.
Ventromedial hypothalamus
What is the ventromedial hypothalamus associated with?
Feelings of Satiety and Hunger
Name this structure in the hypothalamus.
3rd Ventricle
Name this structure in the hypothalamus.
Paraventricular nucleus
What is the function of the paraventricular nucleus?
- Contains nurones that project to the posterior pituitary to stimulate the release of ADH & oxytocin
Name this structure in the hypothalamus.
Arcuate nucleus
What is the arcuate nucleus?
- An aggregation of neuorones in the medial basal part
- Produces both orexigenic and anorexic factors
What are the orexigenic factors released by the arcuate nucleus (2)?
- Neuropeptide Y (NPY)
- Agouti-related peptide (AgRP)
What are the anorexic factors released by the arcuate nucleus (2)?
- Proopiomelanocortin (POMC)
- Cocaine- and amphetamine-regulated transcript (CART)
What regions of the brain (outside the hypothalamus) influence food intake and energy expenditure (2)?
- Amygdala - emotion, memory
- Vagus nerve to brain stem to hypothalamus
What peripheral factors influence food intake and energy expenditure (5)?
- Leptin
- Adipostat
- Ghrelin
- Peptide YY (PYY)
- GLP1 & GLP2
Where is leptin produced?
- Made by adipocytes in white adipose tissue and enterocytes
Leptin concentration is positively correalated with body fat
Where is leptin found?
Circulates in plasma
What is the effect of increased leptin?
- Increased leptin
- Decreased NPY / AgPR in the arcuate nucleus
- Decreased AgPR in arcuate nucleus
- Decreased food intake / Increased energy expenditure through the Melanocortin 4 Receptor (MC4R)
AND
- Increased leptin
- Decreased Melanin-concentrating hormone (MCH) / Orexins in the lateral hypothalamus
- Decreased food intake / Increased energy expenditure through the Melanocortin 4 Receptor (MC4R)
What is leptin resistance?
- POMC deficiency & MC4R mutations cause morbid obesity
No NPY / AgPR mutations associated with appetite disorders in humans
Where is adipostat produced?
Adipose tissue
Where is adipostat found?
Circulating in the blood
What is the function of adipostat?
Acts like a (complicated) thermostat:
* Hypothalamus senses the concentration of hormone
* Hypothalamus alters neuropeptides to increase or decrease food intake
What does ghrelin regulate (4)?
Gherlin is a gastrointestinal hormone
Gastrointestinal hormone: Secreted byenteroendocrine cellsin thestomach, pancreas & SB
- Regulation of reward, taste sensation, memory & circadian rhythm
What is the function of gherlin?
Gherlin is a gastrointestinal hormone
* Gastrointestinal hormone: Secreted byenteroendocrine cellsin thestomach, pancreas & SB
- Stimulates NPY / AgPR neurones
- Inhibits POMC / CART neurones
Increase appetite
When are gherlin levels the highest?
- Before meals: help prepare for food intake by increasing gastric motility and acid secretion
Where is peptide YY (PYY) released and in what response?
- Short pepdite released in the terminal ileum (TI) & colon in response to feeding
What is the function of peptide YY (PYY) (4 steps)?
- Food at terminal ileum & colon
- PYY released
- Inhibits NPY release & stimulate POMC neurones
- Decrease appetite
What is the function of GLP1 & GLP2 (2)?
- Stimulate insulin release
- Inhibit glucagon release
What comorbidities are associated with obesity (10)?
- Depression
- Sleep apnoea
- Bowel cancer
- Osteoarthritis
- Gout
- Stroke
- Myocardial Infarction
- Hypertension
- Diabetes
- Peripheral vascular disease
