Nutrient Intake, Digestion, Absorption, and Excretion Flashcards
Which cells in the GI tract secrete more than 30 GI hormone peptides?
Neuroendocrine cells
What are the major inputs influencing appetite regulation?
Short term signals related to meal ingestion that are transmitted by the “gut-brain” axis
Signals associated with energy stores that are mediated by leptin
Signals deriving from lean body mass
Circadian rhythm
What is the major orexigenic (appetite stimulating) gut hormone?
Ghrelin
Name anorexigenic (appetite suppressing) gut hormones
Glucagon-like peptide-1 and -2 (GLP-1, GLP-2)
Oxyntomodulin (OXM)
Peptide tyrosine-tyrosine (PYY)
Pancreatic polypeptide (PP)
Cholecystokinin (CCK)
How are gut- and fat-derived hormones (ghrelin, leptin, insulin, and PYY) involved in feedback regulation of feeding?
Through signals affecting hunger, satiety, and energy needs
How does ghrelin increase food intake?
By stimulating the ARC of the hypothalamus
Where in the brain are neural and hormonal signals that influence food intake located?
The arcuate nucleus (ARC) of the hypothalamus and the brainstem
Name the site of secretion, stimulating factors, mechanism of action, and effect of GLP-1 (glucagon-like peptide-1)
Distal gut
Stimulated by food intake proportional to energy intake
Works by binding GLP-1 receptors in pancreatic islet cells, heart, lungs, and brain (ARC and PVC)
Reduces appetite and energy intake; delays gastric emptying; enhances postprandial insulin release
Name the site of secretion, stimulating factors, mechanism of action, and effect of OXM (oxyntomodulin)
L cells of the distal gut
Stimulated by food intake
Works as agonist at glucagon receptor; has undefined neural effects
Reduces food intake; increases energy expenditure
Name the site of secretion, stimulating factors, mechanism of action, and effect of PYY (peptide-tyrosine-tyrosine)
L cells of the distal gut
Stimulated by food intake (released in proportion to energy, fat, and protein intake)
Mechanism of action: Y receptors found throughout the CNS and on vagal afferents, NPY (neuropeptide Y) inhibition, POMC (proopiomelanocortin) activation, associated with increased activity of OFC (orbitofrontal cortex)
Reduces food intake
Name the site of secretion, stimulating factors, mechanism of action, and effect of PP (pancreatic polypeptide)
Pancreatic polypeptide cells of the islets of Langerhans in the pancreas
Stimulated by food intake and vagal stimulation
Enters CNS via diffusion in the brain stem and ARC
Reduces food intake
Name the site of secretion, stimulating factors, mechanism of action, and effect of CCK (cholecystokinin)
L cells of the gut, nerves in distal ileum and colon, neurons in the brain
Stimulated by dietary protein and fat, gastric acid
Reduces hypothalamic NPY (neuropeptide Y)
Inhibits gastric emptying and reduces food intake
Name the site of secretion, stimulating factors, mechanism of action, and effect of Leptin
Large amounts from the gastric mucosa; white adipose tissue
Food deprivation is associated with low levels
Low levels influence ARC; possibly decreases gene expression of NPY and increases activity of POMC-secreting neurons
Low levels increase energy intake and decrease energy expenditure
Name the site of secretion, stimulating factors, mechanism of action, and effect of Ghrelin
Stomach
Food intake decreases levels; fasting increases levels
Stimulates ARC via receptors; stimulated GH secretion
Increases food intake
Describe the role of fiber (especially resistant starch R2) on the feeding response
It has satiety value with associated decreases in food intake
True or false: stomach size can influence the amount of food eaten
True. Its size is related to the amount of food habitually eaten.
How is aging associated with decreased appetite and food intake
Likely because of decreased basal hunger rather than increased meal satiety
Name some adverse effects that have been associated with megestrol
Nausea, vomiting, gas, diarrhea
GI muscle fibers are depolarized (contraction of the muscle) in response to?
Stretching of the muscle fiber
Acetylcholine released by parasympathetic neurons
Gut hormones
Inhibition of GI muscle contraction is associated with a hyperpolarized state which is caused by?
Norepinephrine or epinephrine
Sympathetic nerves that secrete norepinephrine
How is the enteric nervous system connected to the central nervous system?
By parasympathetic fibers (stimulates motility) and sympathetic fibers (modulates activity of ENS with inhibitory signals)
Factors that regulate gastric emptying
Volume of food
Gastrin
Enteric gastric nervous reflexes from the duodenum
Ghrelin
Hormonal feedback from the duodenum
What are the neurotransmitters of the ENS?
Acetylcholine
Norepinephrine and serotonin
y-aminobutyrate
Adenosine triphosphate (ATP)
Nitric oxide (NO) and carbon monoxide (CO)
Dopamine
CCK
Substance P
Vasoactive intestinal peptide (VIP)
Somatostatin
Leu-enkephalin
Met-enkaphalin
What are some sensory stimuli in the ENS that are involved in the neural control of the gut?
Irritation of the mucosa, excessive distention, or chemical stimuli