Appetite (Complete) Flashcards by Sydney Carrera-Brown

Give 3 examples of factors that can stimulate thirst

Body fluid osmolality

Body volume reduced

Blood pressure reduced

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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

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When is the sensation of thirst decreased?

Immediately after drinking (even before GI tract absorbs water to correct osmolality)

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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.

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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.

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What effect does reduction in fat mass have on food intake and energy expenditure?

Increases food intake

Reduces energy expenditure

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What effect does adipose tissue expansion have on food intake and energy expenditure

Food intake decreases

Energy expenditure increases

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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

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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)

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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

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Which brain region is important in regulation of appetite?

Hypothalamus

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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

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What 2 things does the hypothalmus play a role in regulating in terms of appetite?

Regulates food intake

Regulates energy expenditure

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The hypothalamus releses peptides which can regulate appetite. Name the peptide which is appetite stimulant.

Orexigenic peptides

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The hypothalamus releses peptides which can regulate appetite. Name the peptide which is appetite suppresive

Anorectic peptides

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Onorexigenic and anorectic peptides are released from which region of the hypothalamus?

Arcuate nucleus

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Which regions of the hypothalamus produces orexigenic peptides?

Lateral hypothalamus (ONLY orexigenic)

Arcuate nucleus (produces both orexigenic and anorectic peptides)

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Which region of the hypothalamus is associated with satiety (fullness)?

Ventromedial hypothalamus

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Lesion in the ventromedial hypothalamus could theoretically lead to?

Severe obesity due to lack of satiety

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Which brain area is involved mainly in the regulation of food intake?

Arcuate nucleus

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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

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What role does the arcuate nucleus have in regulating food intake?

Integrates peripheral and central feeding signals

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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)

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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

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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)