Appetite (Complete) Flashcards
Give 3 examples of factors that can stimulate thirst
Body fluid osmolality
Body volume reduced
Blood pressure reduced
Out of the three main factors that can stimulate thirst, which factor has the most potent effect?
Plasma osmolality increase is the more potent stimulus – change of 2-3% induces strong desire to drink
N.B. Decrease of 10-15% in blood volume or arterial pressure is required to produce the same response
When is the sensation of thirst decreased?
Immediately after drinking (even before GI tract absorbs water to correct osmolality)
Explain why sensation of thirst is decreased immediately after drinking despite water yet being reabsorbed in the GI tract to correct osmolality.
Receptors in mouth, pharynx, oesophagus are involved
N.B. Relief of thirst sensation via these receptors is short lived.
Despite receptors in the mouth and pharynx decreasing thirst, it is only short lived and is completely relieved once?
Thirst is only completely satisfied once plasma osmolality is decreased or blood volume or arterial pressure corrected.
What effect does reduction in fat mass have on food intake and energy expenditure?
Increases food intake
Reduces energy expenditure
What effect does adipose tissue expansion have on food intake and energy expenditure
Food intake decreases
Energy expenditure increases
Explain body weight homeostasis
Body weight is relatively stable for adults
This is due to effects of adipose tissue expansion and fat reduction.
Adipose tissue expansion decreases food intake and increases energy expenditure
Reduction in body fat increases food intake and decreases energy expenditure
Collectively this creates a homeostatic effect in maintaining body weight
In a weight-reduced underfed state, list 5 ways the body tries to re-achieve body weight homeostasis
Reduces sympathetic activity
Reduces thyroid activity
Reduces energy expenditure
Increases appetite
(Ultimately increases body weight)
In a weight-increased overfed state, list 3 ways the body tries to re-achieve body weight homeostasis
Increased sympathetic nervous activity
Increased energy expenditure
Decreased appetite
Which brain region is important in regulation of appetite?
Hypothalamus
List 4 factors which have an input effect on hypothalamic activity in regulating appetite.
Grehilin (Gut hormone)
PYY (gut hormone)
Leptin (fat hormone)
Neural input from the periphery and other brain regions
What 2 things does the hypothalmus play a role in regulating in terms of appetite?
Regulates food intake
Regulates energy expenditure
The hypothalamus releses peptides which can regulate appetite. Name the peptide which is appetite stimulant.
Orexigenic peptides
The hypothalamus releses peptides which can regulate appetite. Name the peptide which is appetite suppresive
Anorectic peptides
Onorexigenic and anorectic peptides are released from which region of the hypothalamus?
Arcuate nucleus
Which regions of the hypothalamus produces orexigenic peptides?
Lateral hypothalamus (ONLY orexigenic)
Arcuate nucleus (produces both orexigenic and anorectic peptides)
Which region of the hypothalamus is associated with satiety (fullness)?
Ventromedial hypothalamus
Lesion in the ventromedial hypothalamus could theoretically lead to?
Severe obesity due to lack of satiety
Which brain area is involved mainly in the regulation of food intake?
Arcuate nucleus
What structural differences does the arcuate nucleus have that enables it to adequately perform its function?
Has an incomplete blood-brain barrier to enable detection of peripheral hormones
What role does the arcuate nucleus have in regulating food intake?
Integrates peripheral and central feeding signals
What are the two neuronal populations in the arcuate nucleus that plays a role in regulating food intake? Which has a stimulatory function and which has an inhibitory function?
Stimulatory population of neurones (Neuropeptide Y (NPY) neurones and Agouti-Related Peptide (AgRP) neurones.
Inhibitory population of neurones (Pro-opiomelanocortin [POMC] neurones)
What hormone plays a role inhibition/stimulation of arcuate nucleus nuerones. And what role does it play?
Leptin
Inhibitis NPY and AGRP neurones
Stimulates POMC neurones
What other hormone besides leptin plays a role in food intake by interacting with arcuate nucleus neurones?
Insulin
Name 3 conditions which can result in activation of food intake mechanisms of the arcuate nucleus.
Genetic leptin deficiency
Uncontrolled diabetes
Fasting
Alongside regulation of food intake, what 2 other things does the arcuate nucleus play a role in?
Fertility
Cardiovascular regulation
Explain how the arcuate nucleus controls food intake.
Arcuate nucleus detects circulating factors (e.g. leption, insulin)
This either activates the stimulating or inhibitorry neurones
POMC is the main inhibitory neurone. When activated, it releases POMC which is converted into one of its biproducts a-MSH (alpha melanocyte stimulating hormone).
a-MSH interacts with MC4R (Melanocortin 4 receptor) in the paraventricular nuclei which triggers a decrease in food intake (e.g. decreased appetie)
Agrp is one of the main stimulatory hormones which when released from Agrp neurones, has an inhibitory effect on MC4R.
Mutations in what 2 things have shown no evidence of effecting appetite in humans?
Mutations in AgRP and NPY
Mutations in what 2 things have shown evidence in affecting appetite in humans?
POMC deficiency
MC4R mutations
What is the effect of POMC deficiency and MC4R mutations in humans?
Causes morbid obesity
N.B. Is not responsible for the prevalence of obesity
Which nerve is responsible in conveying signals from the GI tract to the hypothalamus in refulation of appetite?
Vagal nerve
List 4 brain regions that send signalling to the arcuate nucleus
Higher centres
Lateral hypothlamus, Ventromedial hypothalamus
Vagus to brainstem to hypothlamus
Amygdala (Emotion, memory)
List 2 important functions of the amygdala
Memory
Emotions
Energy expenditure is controlled by which body mechanism?
Adipostat mechanism
Breifly explain how the adipostat mechnaism functtions.
Fat produces and releases circultaing hormones (e.g. leptin)
These hormones reach the hypothalamus which detects concentration of these hormones.
Hypothalamus then alters neuropeptides to increase or decrease food intake.
Where is leptin produced?
Adipocytes in white adipose tissue
What are the two roles of leptin?
Regulates appetite
Regulates thermogenesis (energy expenditure)
N.B. by acting on hypothalamus
Energy expenditure is mainly achieved by a proccess known as?
Thermogenesis
For children with congential leptin deficiency, what medical intervation has been shown to reduce body weight?
Giving leptin
N.B. Very few people have congenital leptin deficiency so cant be used to treat general obesity.
What is the association between leptin and general obesity?
Obese people shown to have reduced sensitivity to endogenous leptin production
What is the relationship between leptin and body fat?
When body fat is low, leptin is low
When body fat is high, leptin is high
Give 3 examples of abnormalities in mechanism of action of leptin that may play a role in obesity
Leptin deficiency (Low leptin)
Regulatory defect (‘Normal’ levels of leptin despite high levels of adipose tissue)
Decrease sensitivity of leptin (High levels of leptin)
Which abnormality in leptin mechanism of action could result in leptin supplements being ineffective as a weigth control drug.
Leptin resistance
What group of hormones play the most prominent role in satiety (feeling full)?
Gastrointestinal hormones
Gastrointestinal hormones are secreted from which cells of the GI tract?
Enteroendocrine cells in the stomach, pancreas and small bowel
List 3 organs which contain enteroendocrine cells responsible for release of gut hormone.
Stomach
Pancreas
SB
What are the 2 main effects of ghrelin?
Stimulates appetite
Increases gastric emptying
Where is ghrelin produced?
Stomach
What is the role of peptid YY? Where is is produced?
Inhbits food intake (satiety)
Produced in small bowel
When is ghrelin levels highest in the blood?
Highest before mealtime
How does ghrelin help to prepare for food intake?
Increasing gastric motility and acid secretion
What effect does ghrelin have on the arcuate nucleus?
Directly modulates neurons in the arcuate nucleus
Stimulates NPY/Agrp neurons.
Inhibits POMC neurons.
Increases appetite
Besides increasing appetite and food intake, list 4 other effects of ghrelin.
Regulation of:
Reward
Taste sensation
Memory
Circadian rhythm
PYY stands for?
Peptide tyrosine tyrosine
Which 2 regions of the body releases PYY?
Terminal ileum
Colon
Can the effects of PYY occur if given through IV?
Yes it doesnt matter if IV injected or digested
Explain how PYY results in reducing appetite.
Inhibits NPY release
Stimulates POMC neurons
List 11 examples comorbidities associated with obesity.
Stroke
Deppresion
Sleep apnoea
Myocardial infarction
Diabetes
Bowel Cancer
Peripheral vascular disease
Gout
What does the diagram suggest?
In healthy environment, both genetically prone and resistant individuals less likely to be obese
In a toxic environment, massive increase in obesity
(Therefore environmental factors play a big role)
