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89 Cards in this Set
- Front
- Back
where does digestion take place
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OUTSIDE our body in the lumenog our GI tract
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Anything that we feel we are aware of, meaning that neurons in the __ are firing
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cerebral cortex
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which brain region is associated with emotional content and memory associated with in eating?
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limbic cortex
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What causes those limbic cortical neurons to begin firing action potentials?
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hypothalamus
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what are the 2 nuclei in the hypothalamus that are assiciated with hunger
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feeding center and the satiety center
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when nuerons in the feeding center excite what is the feeing that is produced?
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the feeling of hunger
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what type of neurons are in the feeding center?
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glucosensitve neurons
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why would glucosensitive neurons fire
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they fire if blood glucose gets low, amongst other inputs
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wehn neurons of the satiety center fire what is produced
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they inhibit the Feeding Center, leading to the lack of hunger (because the Feeding Center stops stimulating the cortex).
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what type of neurons are in the satiety center?
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glucoreceptor neurons
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why causes the glucoreceptor neurons to fire?
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which fire when blood glucose levels are normal or elevated
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what does the arcuate nucleus impact?
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the firing of the fedding center
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what are the two groups of neurons that are located in the arcuate nucleus?
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AGRP Neurons
POMC Neurons |
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what does AGRP stand for
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agouti-related peptide
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what is the function of AGRP neurons?
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which is a potent and long-lasting appetite stimulant; it also decreases metabolism
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HOw does the AGRP Neurons affect the feeding center
whats the affect |
stimulate
generating hunger |
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what does POMC stand for
what type of neurotransmitter is POMC neurons |
Proopiomelanocortin; a polypeptide neurotransmitter
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HOw does the POMC Neurons affect the feeding center
whats the affect |
inhibit
generating satiety |
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do AGRP neurons and POMC neurons inhibits each other as they fire
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yes
will cause the feeling and simultaneously inhibt |
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what inputs stimulate the feeding center
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AGRP Neurons stimulate the Feeding Center
Low blood glucose |
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what inputs inhibit the feeding center?
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POMC Neurons inhibit the Feeding Center
Satiety Center neurons inhibit the Feeding Center Blood glucose inhibits the Feeding Center Insulin inhibits the Feeding Center Mouth touch receptors inhibit the Feeding Center Peptide YY (from the colon) inhibits the Feeding Center |
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The most important input to the Satiety Center is from
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Vagal afferents
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what is the affect of excited vagus afferent on the satiety center
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stimulated the satiety center
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how are vagal afferents stimulated?
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distension of the stomach
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Why do we stop eating once we have begun?
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In large part because stomach distension stimulates the Satiety Center to inhibit the cortical neurons causing us to feel hungry!
Before absorption occurs!! |
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POMC Neurons are stimulated by:
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1) Insulin (a pancreatic hormone released during the “Good Times”)
2) Cholecystokinin (a duodenal hormone released when food, especially fat, enters the duodenum from the stomach) 3) Cocaine (a local anesthetic better known as a drug of abuse) |
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POMC neurons are inhibited by
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1) AGRP Neurons
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AGRP neurons are stimulated
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Ghrelin
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what cells secrete ghrelin
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a polypeptide hormone released by oxyntic cells of the stomach
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why does ghrelin get secreted by oxyntic cells of the stomach
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An empty stomach begins secreting Ghrelin and indirectly produces a feeling of hunger!
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how does lack of sleep affect ghrelin secretion
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increase
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what inhibits the Ghrelin effects?
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while gastric bypass and the Ghrelin receptor antagonist developed as an antiobesity serum inhibit
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AGRP neurons are inhibited by
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insulin and
leptin |
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what is leptin released by?
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adipocytes
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what does leptin also act to do?
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stimulate sympathetic discharge to increase basal metabolic rate
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what is gastrin
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is actually several related short-chain polypeptide hormones
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what secretes gastrin?
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secreted by G cells of the stomach and duodenum.
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gastrin secretion is stimulated by?
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the presence of food in the stomach and/or duodenum
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Gastrin stimulates gastric release of
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hydrochloric acid and, to a lesser extent, also pepsinogen (an inactive precursor of the proteolytic enzyme pepsin).
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what is somatostatin
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a mixture of several related polypeptides
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what cells release somatostatin
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by cells in gastric glands and also by cells of the pancreas (as well as hypothalamic cells).
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what is the primary function of somatostatin?
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to inhibit secretions of the stomach (Gastrin and hydrochloric acid), duodenum (Secretin and Cholecystokinin) and pancreas (Glucagon).
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what does somatostatin do to the rate of nutrient absorption from the digestive tract
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reduce the rate
it slows down digestion |
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what is secretin?
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another polypeptide
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what is secretin released by?
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cells of the duodenum in response to the presence of low pH
chyme has reached the duodenum |
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what is the primary effect of secretin?
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to stimulate the pancreas to release bicarbonate (to neutralize the chyme and thereby allow activation of digestive enzymes).
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what does secretin do to acid secretion and peristalsis
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inhibit
slows allowing the duodenum time to digest the food entering from the stomach |
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what is cholecystokinin
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agroup of similar small polypeptides
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what secreted cholecystokinin?
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are secreted by cells of the duodenum and jejunum
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what triggers the secretion of cholecystokinin?
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primarily in response to the presence of lipids and their catabolites
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what four things does cholecystokinin (CCK) cause in the digestive system?
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stimulates gall bladder contraction (thereby releasing bile into the duodenum for emulsification of lipids, allowing fats to be digested efficiently), stimulates the pancreas to secrete digestive enzymes, slows the rate of gastric emptying (because it takes quite a while to digest fat compared to protein or carbohydrate), and also stimulates the satiety center (as mentioned previously).
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what is vasactive intestinal polypeptide (VIP)
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is a polypeptide hormone that is more of a neurotransmitterbut is released at loose synapses and can also be called a hormone
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VIP causes what affect in vessels of the gastrointestinal tract during digestion
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vasodilation
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VIP produces vasodilation in response to what neural system?
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increased parasympathetic input to the enteric nervous system
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what are 3 of the significance of the vasodilation caused by VIP?
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assuring that the active cells receive sufficient oxygen for working and also sufficient plasma as the precursor for enterocytes (small intestine cells) to produce mucous secretions. Finally, the increased blood flow also assures that nutrients can be efficiently absorbed from the gut.
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what nervous system plays an important role in regulating gastrointestinal function
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CNS
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outflow of CNS system that regulated gastroint fun't is carried by what nervous system
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autonomic nervous system
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which part of the autonomic nervous system is more active in gastro fun't
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parasympathetic > symp
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what does much of the autonomic outfllow moderate?
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does not directly innervate gastrointestinal cells, but instead moderates the activity of the Enteric Nervous System (ENS).
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where does the ENS run from
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runs much of the length of the digestive tract (from part way down the esophagus until the external anal sphincter) and consists of about as many neurons as are present in the spinal cord.
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what are the two layers (plexuses) that the ENS are divided into?
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myenteric (Auerbach's) Plexus
SUbmucosal (Meissner's) plexus |
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what does the myenteric plexus regulate and what is the result of this?
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primarily regulates contractions of smooth muscle that result in peristalsis and sphincter control.
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what does the submucosal plexus regulate
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neurons are associated with regulation of secretions and blood flow along the length of the digestive tract.
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what type of neurons do the plexuses of the ENS have?
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contain not only motor neurons (for producing secretions and muscle contraction), but also interneurons for coordinating functions (local control) and sensory neurons (to provide information from the gut back to the CNS).
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what type of stimuli do the different receptors of the ENS respond to
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mechanical (stretch and tension), thermal (heat and cold), osmotic and chemical (glucose and amino acids) stimuli.
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how is sensory information primarily conveyed to the CNS
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afferent fibers of the vagus
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Parasympathetic outflow to the gut includes?
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Glossopharyngeal (IX) and Facial (VII) nerves innervating salivary glands, the vagus innervating much of the length of the digestive tract, and sacral nerves innervating the colon.
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what innervates the salivary glands
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IX and VII
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what innervates much of the length of the digestive tract
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vagus
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what innervates the colon
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sacral nerves
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Sympathetic innervation of the salivary glands travels through what ganglion
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superior cervical ganglion
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what nerves conduct impulses to much of the rest of the GI tract
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splanchnic nerves
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how are digestive reflexes named?
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for the site of initiation followed by the site affected
ie Therefore, the gastrocolic reflex refers to how food entering the stomach (“gastro”) results in increased motility of the colon (“colic”) |
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what components are in mouth secretions?
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saliva
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what components are in esophagus secretions?
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The esophagus secretes mucous throughout the length of the esophagus.
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what is the function of mucous in the esophagus
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function of the mucous is lubrication (to facilitate the movement of food from the mouth to the stomach) and also protection against excoriation (scraping) and acidic erosion of the lower portion of the esophagus.
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how is mucous in the esophagus differ from the top vs the bottom of esophagus
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mucous is thicker and contains a higher level of bicarbonate (for acid neutralization) at the gastric end of the esophagus
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what does the stomache secrete into the lumen of the digestive tract?
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gastinr, Hydrochloric acid, pepsinogen, mucous, gastroferrin (for facilitating iron absorption) and Intrinsic Factor (essential for vitamin B12 absorption).
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what is the function of gastroferrin
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for facilitating iron absorption
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what are the fun't of intrinsisc factor
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essential for vitaminB12 absorption
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what are the hormones released in the blood by the small intestines?
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secretin and cholecystokinin
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what are secreted into the lumen of the small intestine
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serous mucous and bicarbonate-enriched mucous, lysozyme, and defensins (the later two serving antibacterial functions
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what is secreted by the colon
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Mucin-rich mucous is pretty much the whole story for secretions by the colon
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what hormones does the pancreas secrete into the blood
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insulin, glucagon and somatostatin
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what digestive enzymes does the pancreas secrete into the lumen of the gastro tract
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Trypsinogen, Chymotrypsinogen, Procarboxypeptidase A and B, Pro-elastase (all of the preceding are inactive precursors of proteolytic enzymes), Pancreatic Lipase, Pancreatic Amylase, and Ribonucleases
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what does the pancreas secrete about 2 liters/day
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bicarbonate-rich fluid (used to neutralize the acidic chime coming from the stomach).
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what does the liver synthesizes and releases into the blood?
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plasma proteins, VLDLs (very low density lipoproteins) and HDLs (high density lipoproteins
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what is bile consist of
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bile salts and bile acids for lipid emulsificationand
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what compound does bile serve as an avenue for excretion
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bilirubin from heme breakdown
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