1b Appetite Flashcards
What are the three things which stimulate thirst?
- Body fluid osmolality
- Blood Volume lowers
- Blood Pressure lowers
Which of the three stimuli for thirst is the most potent?
An INCREASE in plasma osmolality
Which hormone is the main regulator for osmolality?
ADH or Vasopressin
Where does ADH act?
Via the aquaporin 2 channel in the kidneys - renal collecting duct
Where is ADH stored
posterior pituitary gland
ADH is secreted through neurons in what region of the brain?
Hypothalamus
What regions are the sensory osmoreceptors found in the hypothalamus?
Organum vasculosum of the lamina terminalis (OVLT)
Subfornical Organ (SFO)
- Describe the process that leads to ADH release initiated by osmoreceptors
- When plasma is more concentrated, water moves out the osmoreceptors, causing them to SHRINK
- This means the PROPORTION OF CATION channels in the membrane increases - membrane depolarises
- Send signals to the ADH producing cells to increase ADH → Fluid retention, Invokes drinking
When is thirst completely satisfied?
Thirst is only completely satisfied once plasma osmolality is decreased or blood volume or arterial pressure corrected.
Which receptors are involved in the sensation of thirst?
Receptors in mouth, pharynx, oesophagus are involved - relief of thirst via these is short lived
How does the renin-angiotensin system REACT to a decrease in blood pressure?
- Juxtaglomerular cells of renal afferent arteriole, once the decreased blood pressure here is detected, will release renin
- cleaves angiotensinogen in the liver to release angiotensin I
- Angiotensin I is converted into Angiotensin II in the lungs
- Angiotenin II Binds to receptors on the intraglomerular messenger cells
- This binding causes these cells to contract along with the blood vessels surrounding them, which then leads to release of aldosterone in the zona glomerulosa of the adrenal cortex
This increases blood pressure
What are the four functions of angiotensin II?
Induces thirst
ADH secretion as well
Vasoconstriction, increase in sympathetic activity
H2O retention via NaCl absorption and K+ excretion
What 2 types of drugs that affect the RAAS are known to treat high blood pressure?
ACEi
Direct Renin Inhibitors
How does weight homeostasis work in an overfed state? (Adipose tissue expansion)
- Increased sympathetic activity
-Increased energy expenditure
-Decreased hunger and food intake
How does weight homeostasis work in underfed state? (Reduction in fat mass)
Increased hunger and food intake
Decreased energy expenditure
Decreased sympathetic nervous system activity
Decreased thyroid function
What system defends against reduction of body fat?
Central Circuit Defence
What system defends against rapid expansion?
Yet to be discovered
What is the significant hormone involved in the central circuit defense against reduction of body fat?
Leptin
Where does the most important regulation of appetite occur?
Hypothalamus
What are the two main gut hormones involved in the regulation of appetite?
GHRELIN, PYY & other gut hormones
Which nerve do signals from Ghrelin and PYY travel to the brainstem via?
Vagus nerve
Other than the gut hormones through vagus nerve, how else does the hypothalamus receive input about appetite regulation?
Neural input from the periphery and other brain regions
Leptin
What part of the hyopthalamus is the most important site in regulation of food intake? Describe it also.
Arcuate nucleus - An aggregation of neurones in the medial basal part of the hypothalamus
What is the name of the nucleus in the hypothalamus that has neurons projecting to the posterior pituitary?
Paraventricular nucleus
