PAT 4: Hunger and Satiety
What are some other functions of GHRELIN?
- stimulation of GI motility - maintanance of energy homeostasis - impact on reproduction - involved with stress response and modulation of immune pathways
What is the result of distention of the GI tract on eating behavior?
- vagal afferents suppress the feeding center
What acts as the brain's satiety center?
- ventromedial hypothalamus (VMH)
Can leptin cross the Blood Brain Barrier (BBB) ?
- yes - can cross via facilitated diffusion
List some peripheral inputs to the hypothalamus which inhibit food intake? Stimulate?
Inhibition: - gastric distention (stretch receptors) - PYY - CCK - Insulin - Leptin Stimulation: - GHRELIN
_______ is a natural antagonist of melanocortins receptors (MCR-3 / MCR-4)
- Agouti-related protein (AGRP)
List examples of chemical factors that inhibit the feeding center
- Cholecystokinin (CCK) - Peptide YY Incretins: - Glucagon like peptide 1 (GLP1) - Gastric inhibitory polypeptide (GIP)
Where is leptin produced?
- adipose cells (as they increase in size = food intake inhibition)
Leptin initiates actions that ______ fat storage
- decrease
What actions are initiated by leptin that decrease fat storage?
- decreased production of appetite stimulators (NPY and AGRP) - increased production of CRH - increased sympathetic nerve activity - decreased insulin secretion
What secretes Peptide YY?
- enteroendocrine cells of illeum and duodenum
Excessive formation of AGRP (due to gene mutation) leads to _________
- excessive eating - obesity
From where is GHRELIN secreted?
- gastric X/A-like endocrine cells - hypothalamic neurons (some) - in intestines - in pancreas (epsilon cells)
______ feeding will result in inhibition of melanocortin pathway
- increased
What hormones inhibit Neuropeptide Y?
- insulin - PYY - leptin
What acts as the brain's hunger center?
- lateral hypothalamus (LH)
When is CCK released?
- mainly in response to fats in the duodenum
The ______ pathway plays a powerful role in regulating energy balance
- melanocortin pathway (defective signals cause extreme obesity)
What is the most common known cause of obesity?
- mutations of Melanocortin-4 receptor (MCR-4) (responsible for 5-6% of obesity in children)
What is GHRELIN?
- potent stimulator of food intake blood levels: - rise with fasting - rapidly drop after meal (gastric secretion ceases within an hour of eating)
Taste and smell receptors ______ hunger
- stimulate (effect is short lived due to very fast adaptation of receptors)
What do incretins GLP1 and GIP do?
- stimulate insulin secretion - supress appetite
What are the effects of CCK?
- stimulates secretion of bile - stimulates secretion of pancreatic enzymes - stimulates brain and sensory fibers of CN X (suppresses appetite)
True or False: Leptin stimulates secretion of melanocortin peptide
True
Define anorexigenic signals. Give examples
Anorexigenic signals: supress food intake and increase energy expenditure - α-melanocyte stimulating hormone (α-MSH) - cocaine and amphetamine-regulated transcript (CART) - Peptide YY (PYY) - leptin
What is the body's preferred form of energy for breakfast? Why?
Breakfast: carbohydrates - blood concentrations of norepinephrine and corticosterone - both are appetite stimulants (when in paraventricular region of brain) - both facilitate carbohydrate intake
What is the body's preferred form of energy for lunch? Why?
Lunch: proteins - appetite increased by Growth hormone Releasing Hormone (GhRH)
What do the two neural networks located on the arcuate nucleus of the hypothalamus secrete?
One group: - secretes neuropeptide Y (NPY) (potent appetite stimulant) Other group: - secretes melanocortin (inhibits eating)
Define orexigenic signals. Give examples
Orexigenic signals: stimulate food intake and decrease energy expenditure - Neuropeptide Y (NPY) - Agouti-related protein (AGRP) - GHRELIN
What are the functions of Peptide YY?
Primary effect: signal satiety and terminate eating (stop eating signal) - higher levels observed after meal with high fat content - secreted with eating = proportional to calories consumed
Melanocortin-4 receptor (MCR-4) for satiety signals is stimulated by ________ and inhibited by _______
Stimulated: α-melanocyte stimulating hormone (α-MSH) Inhibited: Agouti-related protein (AGRP)
What is the effect of stimulation of the ventromedial hypothalamus (VMH)? What is the effect of a lesion?
Stimulation: decreases eating Lesion: increases eating
What is the effect of stimulation of the lateral hypothalamus (LH)? What is the effect of a lesion?
Stimulation: increases eating Lesion: decreases eating
What is the body's preferred form of energy for supper? Why?
Supper: fats - stimulation with aldosterone
True or False: GHRELIN stimulates Neuropeptide Y (NPY) secretion
True
True or False: GHRELIN stimulates release of GH?
True
