Regulation of Food Intake Flashcards
What are the short-term mechanisms of regulation?
Distension of stomach
GI hormones
Prevents overeating each meal
What are the long term mechanisms of regulation and their role?
Mediated by blood glucose levels (insulin/glucagon)
Maintains normal quantities of energy stores in body
What is the role of the lateral nuclei in food intake?
Feeding center
Stimulation causes hyperphagia
Destruction causes lack of sire for food and progressive weight loss - ination
What is the role of the ventromedial nucleus in food intake?
Satiety center
Stimulation can cause complete satiety and lack of eating - aphagia
Destruction causes voracious and continuous eating
What is the role of the paraventricular nucleus in food intake?
Lesions cause excessive eating
What is the role of the dorsomedial nucleus in food intake?
Lesions usually depress eating behavior
What is the role of the arcuate nucleus in food intake?
Site where hormones released from GI tract and adipose tissue converge to regulate food intake and energy expenditure
Contains proopiomelanocortin neurons and NPY-agRP neurons
What are proopiomelanocortin neurons (POMC)?
Produce both:
a-melanocyte-stimulating hormone (a-MSH)
cocain-amphetamine-regulated transcript (CART)
Activation decreases food intake and increases energy expenditure
What are NPY-AgRP neurons?
Produce neuropeptide Y (NPY) and agouti-related peptide (AgRP)
Actiavtion increased food intake and reduces energy expenditure
What are MCR-3 and MCR-4 receptors?
Located in the paraventricular nucleus
POMC neurons release a-MSH, which stimulate these receptors
Activation reduces food intake and increases energy expenditure
Inhibition increases food intake and decreases energy expenditure
What can occur due to CART mutations?
Obesity
How does the melanocortin system regulate energy stores in the body?
Defective signaling associated with extreme obesity
Mutations in MCR-4 most common cause of monogenic human obesity
Activation of melanocortin system reduces appetite
What is the role of AgRP released from orexigenic neurons?
Antagonist of MCR-3 and MCR-4
Increases feeding by inhibiting effects of a-MSH
Release inhibited by insulin
Excessive formation of AgRP due to mutation associated with excessive feeding and obesity
What is the role of NPY released from orexigenic neurons?
Binds to Y receptors
Stimulates appetite when energy stores are low
Firing of POMC neurons reduced
What is the function of Hypocretin/orexin?
Promotes food intake
Expression increased during food deprivation
Neurons more active during fasting
What is the role of the NTS in food intake?
Responds to peripheral circulating signals and receives vagal afferents
High density of Y receptors
Satiety center present
What is the effect of nicotine on the regulation of food intake?
Nicotinic AChRs located on POMC neurons, which enhance firing of POMC and release of a-MSH
a-MSH reduces food intake and increases energy expenditure
What is the function of Leptin?
Produced by adipocytes
Anorexigenic effects on hypothalamus
Output increased by insulin; inhibited by fasting and weight loss
Increases SNS activity, increasing energy expenditure
What is the function of CCK?
Anorexigenic
Inhibition of gastric emptying, also affect the brain
What is the function of Ghrelin?
Produced primarily by stomach and proximal small intestine
Orexigenic (only one)
Stimulates NPY/AgRP neurons
Levels increase with weight loss, stress, and sleep deprivation
What is the function of Glucagon-like peptide-1 (GLP-1)?
Produced by L cells in ileum and colon from proglucagon
Released in biphasic fashion in response to nutrient load: early-minutes, late- 1 hour
Anorexigenic
Delays gastric emptying, activates a-MSH/CART neurons
What is oxyntomodulin (OXM)?
Proglucagon-derived peptide secreted from distal intestine
Anorexigenic
What is the function of PYY?
Secreted by L cells in intestine after meal in proportion to caloric load
Reduces gastric emptying and delays intestinal transit
Anorexigenic
What are the long-term effects of glucose?
Increases firing of neurons in satiety centers in VMN and PVN
Decreases firing of neurons in hunger center of lateral hypothalamus
What is the effect of the endocannabinoid system on food intake?
Receptor in hypothalamus binds THC
Stimulates orexigenic system in hypothalamus
Stimulates cravings
What is the effect of aging on food intake?
Orexigenic substance levels go down
Anorexigenic substance levels stay the same
What is anorexia nervosa?
NPY levels elevated, leptin levels decreased
LEvels will return when weight goes back to normal
