Appetite Flashcards
What are the three stimuli that induce thirst?
Blood plasma osmolality increased
Blood volume reduced
Blood pressure reduced
Osmolality vs Osmolarity
Osmolarity refers to the number of solute particles per 1 L of solvent, whereas osmolality is the number of solute particles in 1 kg of solvent
Which of these is the most potent stimulus?
Blood plasma osmolality
What hormone is responsible for the homeostasis of blood osmolality and how does it do this?
ADH/Vasopressin - migrates to collecting duct and stimulates integration of aquaporin 2 receptors on apical side of collecting duct
ADH and urine output
High ADH = low urine output
Low ADH = high urine output
What are osmoreceptors
Sensory receptors that control osmoregulation.
Found in the hypothalamus
sensitive to blood osmolality
Which specific region of the hypothalamus are osmoreceptors found?
Subfornical Organ (SFO)
Organum Vasculosum of Lamina Terminalis (OVLT)
Describe the mechanism of ADH release at the site of osmoreceptors
Cells become hypotonic and shrink
Proportion of cation channels increases due to less SA
Positive charge influx results in ADH production
Fluid retention via drinking
When is thirst truly satisfied?
Plasma osmolality decreased or blood volume increased
Why is sensation of thirst important?
Time rq for water to reach the GI tract and plasma osmolality to be corrected.
Sensation provides short term relief and prevents excessive fluid intake - affect salt balance
Describe the renin angiotensin system
Low BP -> renin release from juxtaglomerular cells, converts angiotensinogen into angiotensin I in the liver, which is converted to angiotensin II by ACE.
What are the 4 effects of angiotensin II?
Thirst,
ADH secretion,
Vasoconstriction (sympathetic activation),
Aldosterone (using Na/K pump for H2O retention), Nacl absorption and k+ excretion
The impact of the change in fat mass
Increase in fat mass causes
- increased sympathetic activity
- increased thyroid function
- decreased appetite
What are the two nuclei in the hypothalamus involved in appetite control?
Arcuate Nucleus,
Paraventricular Nucleus
What is the function of the arcuate nucleus?
aggregation of neurons in the mediobasal hypothalamus
Store of neural peptides (NPY/AGRP , POMC)
Orexigenic peptides
Appetite stimulant neural peptides
Anorectic peptides
Appetite suppressive neural peptides
What is the function of the paraventricular nucleus?
Controls appetite and energy expenditure
Neurons project to posterior pituitary secreting vasopressin and oxytocin
Function of the lateral hypothalamus
Produces orexigenic peptides (stimulant)
L - Loves food
Function of the ventromedial hypothalamus
Associated with hunger
V - aVoids food
What structural property of the arcuate nucleus allows it to be able to respond to the peripheral environment?
Incomplete blood brain barrier, access for peripheral hormones
Neurons in the stimulatory pathway of ARC nucleus
- appetite stimulus
Neuropeptide Y (NPY),
Agouti-related Peptide (AGRP) - inhibits POMC
Neurons in the inhibitory pathway of the ARC nucleus
- appetite suppression
Pro-opio melanocortic hormone (POMC)
Describe the hunger inhibitory pathway release of neural peptides on MC4R?
POMC is released from ARC, then converted to alpha-MSH, moves through third ventricle into paraventricular nucleus, binding to MC4R
