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
What is meant by orexigenic?
Appetite Stimulant
What term is used to describe an appetite suppressor?
Anorectic
how does the arcuate nucleus allow access to peripheral hormones?
Incomplete blood brain barrier
Where are orexigenic peptides produced?
The lateral hypothalamus
What is the ventromedial hypothalamus involved with?
Satiety - the feeling of being full
where in the hypothalamus are melanocortins found??
Ventromedial hypothalaus
Which neurones form part of the stimulatory system in the arcuate nucleus?
NPY/AGRP neuron
Which neurones form part of the inhibitory system in the arcuate nucleus?
POMC neurone
Which mutations cause morbid obesity in humans?
POMC deficiency and MC4-R mutations cause morbid obesity.
What effect does the amygdala have on appetite?
Plays a strong role in the reward-motivation pathways in the brain
Regulating appetite with response to emotions
How does the adipostat mechanism work?
Circulating hormones (can be leptin) are produced by adipose tissue
The more adipose tissue → the more hormones being produced
Hypothalamus senses the concentration of hormone
Hypothalamus uses this to alter neuropeptides to increase or decrease food intake
What effect does leptin have on appetite?
Leptin decreases appetite
What effect does leptin have on maintaining body temperature and therefore expenditure?
Leptin increases thermogenesis
This therefore increases energy expenditure
Where is leptin produced?
adipocytes in white adipose tissue and enterocytes
What are the level of leptin when the body fat is low and high?
Low when low, high when high
What are the gastrointestinal hormones that regulate appetite released by?
Secreted by enteroendocrine cells in the stomach, pancreas & SB
What are the two gut hormones which control appetite?
Ghrelin and PYY
What is the overall function of ghrelin?
Stimulates appetite, increases gastric
emptying
What are the functions of ghrelin in the gastrointestinal tract?
Increase gastric motility
Increase acid secretion
how specifically does ghrelin affect appetite?
Directly modulates neurons in the arcuate nucleus to increase appetite
Stimulates NPY/Agrp neurons
Inhibits POMC neurons
When are levels of ghrelin highest in the body?
Before a meal
other than appetite what does ghrelin regulate?
Regulation of reward, taste sensation, memory, circadian rhythm
What method is used to measure the levels of ghrelin throughout the day?
Radioimmunoassay
What is the rhythm of ghrelin release?
Diurnal
Rising throughout the day to highest at 8am, 12pm and 4pm
Lowest at 9am
What is PYY?
Peptide tyrosine tyrosine
Where is PYY released?
Short peptide released in the terminal ileum (TI) and colon in response to feeding (36 Amino acids)
what effect does PYY have on appetite?
Reduced appetite
How does PYY reduce appetite?
- Inhibits NPY release
- Stimulates POMC neurons
What types of foods initiates the best PYY response?
Dietary fibres, wholegrains, and enzymatic breakdown of crude fish proteins
What are some of the side effects of PYY?
Nausea, fullness especially with higher dose
Less hunger and early fullness in the premeal period during PYY infusions
What are some of the comorbidities with obesity?
Stroke
Depression
MI
Hypertension
Bowel Cancer
Gout
OA
Sleep Apnoea
Other than bowel cancer, what other cancer is suspected of being related to obesity?
Breast
What 2 categories of risk factors lead to an increase in obesity?
Genetic and environmental
