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345 Cards in this Set
- Front
- Back
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process by which a gland or glands release water and other substances (enzymes, hormones) into the GI tract |
secretion |
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process by which contractions of smooth muscle in the wall of the GI tract mix and propel contents form the oral to anal direction (usually) |
motility |
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process by which large molecules are cleaved into small molecules appropriate in size for actions of digestive enzymes and or absorption |
digestion |
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process by which nutrients (water, ions, breakdown products of CHO, fats, and proteins) are absorbed by cells of the GI tract |
absorption |
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about __% of immunoglobulin producing cells are in the small intestine |
80 |
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what are the 5 functions of the GI tract |
secretion, motility, digestion, absorption, immunity |
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what are the seven hollow organs of the GI tract? |
oropharanx, esophagus, gallbladder, small intestine, stomach, colon and rectum |
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__ is found in the saliva of the mouth which digests starch |
amalyase |
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a simple conduit for the movement of food from mouth to stomach. has no digestive functions |
esophagus |
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organ used for storage, mixing and digestion of food |
stomach |
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where a concentrated solution of bile salts is stored |
gallbladder |
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where the final stages of chemical enzymatic digestion occurs and where almost all of teh nutrients are absorbed |
small intestine (duodenum, jejunum, ileum) |
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where water is resabsorbed, bacterial fermentation takes place, and feces are formed and stored |
colon and rectum |
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what are the three solid organs of the digestive tract? |
salivary glands, liver, pancreas |
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what are the three salivary glands? |
parotid, sublingual, submandibular |
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what are the two functions of the salivary glands? |
release saliva and salivary amylase |
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what is the major role of the liver in digestion? |
produce bile |
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__ divide the gut into functional segments under varying CNS control |
sphincters |
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separates the pharynx from the esophagus and prevents the movement of food from esophagus back into the mouth |
upper esophageal sphincter |
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the __ opens to pressure generated by the bolus of food pushed back to pharynx (swallow reflex) |
upper esophageal sphincter |
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the lower esophageal sphincter is also called the __ |
gastroesophageal sphincter |
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the __ is located between the esophagus and stomach and prevents the movement of acid and contents of stomach from entering the esophagus |
lower esophageal sphincter |
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disorders of the __ include gastroesophageal reflux disease (GERD) and achalasia |
lower esophageal sphincter |
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is mainly caused by transient, inappropriate relaxation of, and or low maintained pressure of LES
typical symptoms include heartburn at least 2x per week for 4-8 weeks
can lead to mucosal damage and esophageal erosion |
gastroesophageal reflux disease (GERD) |
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what are two treatments of GERD? |
proton pump (H-K-ATPase) inhibitors
antihistamines |
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where the lower esophageal sphincter fails to relax and peristalsis can be impaired in distal esophagus
probably related to loss of vagal inhibitory fibers, preventing relaxation of LES
pt has difficulty swallowing (dysphagia) and bag-like protrusion forms in esophagus |
achalasia |
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seperation between the stomach and teh small intestine |
pyloric valve |
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regulates the movment of chyme from stomach into the small intestine |
pyloric valve |
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the __ acts gradually, allowing for adequate digestion in a sieving action (larger particles retained for further breakdown) |
pyloric valve |
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prevents the movement of materials from small intestine back to stomach |
pyloric valve |
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food from the mouth to the esophagus is called __ |
bolus |
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once bolus is in the stomach, it is called __ |
cyme |
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wrinkles in the stmach lining which help expand the stomach for mixing and grinding |
rugae |
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controls exit of the common bile duct and pancreatic duct into the duodenum |
sphincter of oddi |
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produces contraction of teh gallbladder to drive bile salts down the duct and into the duodenum |
cholecystokinin (CCK) |
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when cyme enters the duodenum, the __ prevents the movement of contents from duodenum into the common bile duct and pancreatic duct |
sphincter of oddi |
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contains a thickened band of circular smooth muscle
prevents movement of fecal material out through the anus unless the external anal sphincter is relaxed |
internal anal sphincter |
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the interanl anal sphincter is under __ control |
involuntary |
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the external anal sphincter is comprised of __ muscle, maintains a significant __ and is under __ control |
striated, resting tone, voluntary |
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the submucosa has the __ nervous system embedded in it |
enteric |
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name the layers of the wall of the digestive tract |
lumen--mucosa--submucosa--submucosal plexus--circular muscle--myoteric plexus--longitudinal muscle--serous membrane layer |
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innermost layer of GI tract, composed of epithelium, lamina propria (layer containing blood vessels, neurons, and immune cells) and muscularis mucosa (contrls folding of the mucosa) |
mucosa |
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layer that lies between the muscularis mucosa and the circular muscle layer. composed of loos connective tissue containing larger blood vessels, lymphatics, and may contain glands of secretion |
submucosa |
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the most important part of the submucosa is the __ |
submucosal plexus |
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what is the function of the submucosal plexus? |
mechano and chemo sensory info
secretion |
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the innermost muscular layer of the small intestine |
circular musclular layer |
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the outermost muscular layer of the gut tube |
longitudinal muscle layer |
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a group of enteric nervous system neurons between the longitudinal and circular muscle layers controls GI movements |
myenteric plexus |
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outermost layer of the GI tract, consists of a thin layer of loose connective tissue covered by mesothelium. also called tunica adventitia outside the abdomen, also makes up the mesentery in teh abdomen |
serosa |
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invaginations of the epithelial layer and GI wall in teh large intestine |
cyrpts |
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finger like projections into the lumen in teh large intestine |
villi |
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create the brush boarder of the large intestine |
microvilli |
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the __ has just crypts, the __ has crypts and villi |
large intestine, small intestine |
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the mucosa of the large intestine have __ cells which secrete mucin and mucus and __ cells which help repopulation the epithleium |
goblet, stem |
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the stem cells of the large intestine turn over every __ |
4-5 |
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why do cancer pt have a lot of GI problems? |
chemo drugs kill the stem cells which repopulate the GI epithelium |
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the GI system has neural control from the __ and __ systems |
CNS (extrinsic), ENS (intrinsic) |
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the enteric system is composed of the __ and __ plexi |
myenteric, submucosal |
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controls the longitudinal and circular smooth muscle and does some secretion |
myenteric plexus |
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the grinding and cutting up of food with your teeth to break food up into suitably-sized particles for swallowing |
chewing (mastication) |
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why do you need to chew food to break it up into smaller particles? |
smaller particles=greater surface area for enzymes to work on |
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chewing is espeically important for what kind of food? |
plant material |
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__ helps lubricate food and and starts chemical digestion with salivary amylase |
saliva |
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muscles for chewing are innervated by a motor branch of the __ cranial nerve |
5th (trigeminal) |
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chewing is controlled by __ |
nuclei in the brainstem |
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describe the chewing reflex |
food in the mouth causes reflex inhibition of muscle of mastication, causes mouth to drop
when jaw drops, stretch reflex of jaw muscles cause rebound contraction to raise jaw and close teeth
rebound contraction of jaw pushes bolus of food to roof of mouth, initiates another reflex inhibition of jaw muscles to drop jaw again
process continues until bolus is voluntarily pushed to back of mouth when swallowing reflex is initiated |
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describe the two stages of deglutition |
buccal (voluntary) stage: rolling up of bolus and moving it to the phayrnx
pharyngeal (involuntary) stage: soft palate moves up so food can't enter nares
palatopharyngeal folds pulled to center to regulate particle size
larynx pulled upward and anterior
epiglottis closes over trachea
upper esophageal spinger relaxes
esophageal peristaltic contraction |
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the pharynx is under __ contrl allowing coordination of swallowing, speech, and respiration |
CNS |
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explain the innervation of the esophagus |
upper third is controlled by CNS (striated muscle) uses somatic nerves releasing ACh, activating nicotinic receptors causing contraction
lower 2/3's is smooth muscle controlled by the enteric nervous system and vagus nerves (parasympathetics) |
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sequential contraction and relaxation of the esophagus |
peristaltic wave |
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explain how peristalsis works in the esophagus |
streth of wall stimulates ENS to contract gut wall 2-3 cm upstrearm, behind the bolus
contractile ring forms and propagates propelling food forward
ENS causes relaxation of gut wall downstream helping food move towards the anus |
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explain how the gut contracts is muscular layers to move the bolus of food via peristalsis |
stretch/distension of gut wall by bolus--activation of sensory neuron--activation of cholinergic interneurons--activation of excitatory neuron to cause contraction of circular muscle and relaxation of circular muscle upstream--actication of inhibitory motor neuron to cause relaxation of circular muscle and contraction of longitudinal muscle dowstream |
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what does the circular muscle and longitudinal muscle do in the gut? |
circular muscle contracts to move the bolus of food via parstalsis
contraction of longitudinal muscle downstream bunches up intestines closer to bolus, relaxation upstream helps bolus let go and move down |
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why is low pH a good stimulus for parastalsis? |
b/c it allows perastalsis to restart and push back stomach acid out of the esophagus |
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explain pressures in the esophagus during peristalsis |
rest: pressure in UES is 15 mmHg
bolus pushed back at pharynx, increases pressure to 30-100 mmHg
UES opens, food moves into esophagus, starts peristaltic wave
LES relaxes to allow food into stomach |
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what are the two phases of peristalsis? |
primary: primary wave that moves down the esophagus, produces a reflex relaxation int eh lower esophageal sphincter and food moves into the stomach
secondary persitalsis: secondary wave initiated if food remains in esophagus after primary wave (by ENS) |
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what is the role of the LES in persitalsis? |
normally constricted
peristaltic waves open sphincter and then it closes to prevent movement of acid into esophagus
alcohol, caffeine, nicotine, anesthetics will inhibit contraction LES and produce the feeling of heartburn |
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explain receptive relaxation of the stomach |
as food moves into the stomach a vagal reflex produces relaxation of teh wall of the stomach to allow more food to enter |
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explain how the stomach mixes food |
weak peristaltic waves mix food with pepsin and HCL to begin digestion
upper part of stomach show low frequency, sustained contractions which generate basal pressure with the stomach
tonic contractions generate a pressure gradient from the stomach to small intestine, responsible for gastric emptying
as food is mixed, it takes on milky appearance and is called cyme |
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the upper half of the stomach has __ contractions, while the lower half has __ contractinos |
tonic, phasic |
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explain gastric emptying |
lower stomach has strong peristaltic waves that increase in amplitude as they propagate towards the pyloric sphincter
occur 3 times/min
driven by intrinsic electrical activity (pacemaker cells) plus stimulatory NT release from enteric nerves activated by gastric distention
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during gastric emptying, as the chyme moves closer to the pyloric valve, contractions called the __ squirt small quantities of chyme trough the pyloric valve and into the duodenum |
pyloric pump |
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__ and __ increases gastric motility |
distention of stomach, gastrin |
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__, __, __, and __ inhibit emptying of the stomach |
stretch on the duodenum, acid, fat, carbohydrates |
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__ readily pass throught eh pyloric valve but __ must be reduced to a diameter of about 1-2 mm. |
liquids, solids |
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if a solid is larger than 1-2 mm it is repelled by teh pyloris and is __ |
squirted back to stomach for more grinding |
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the expulsion of gastric contents and often, the proximal small intestine |
vomiting |
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what are the three steps of vomiting? |
nausea/dizziness and or stretching
retching
emesis |
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what is the process of emesis? |
deep breath--glottis is closed and larynx is raised to peon UES--soft palate raised to close off posterior nares--diaphragm contracted downward to create negative pressure, opens LES--abdominal muscles contract--stomach content is squeezed and pyloric valve forces stomach contents up teh esophagus |
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gastic motility in the small intestine is characterized as a series of __ in which cyme is moved down the GI tract by the __. these occur in any part of the intestine and move towards large intestine in at about __ cm/sec. |
propulsive movment, persitaltic wave, .5-2 |
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speed of peristalsis in teh small intestine is faster in teh __ and slower in the __ |
duodenum, ileum |
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the average speed of cyme through the small intestine is about 1cm/min, so it takes about __ hours for food to move from teh pyloric valve to the ileocecal valve |
3-5 |
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what two things increase peristalsis in the small intestine? |
entry of chyme into the duodenum, gastroenteric reflex |
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explain teh gastroenteric reflex |
intitated by distension of stomach
conducted through myenteric plexus from stomach down the wall of small intestine |
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what three things can enhance intestinal motility in the small intestine? |
gastrin, serotonin, CCK |
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what two things can inhibit motility |
secretin, glucagon |
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once cyme passes through teh small intestine (3-5 hours) it reaches the __ where it can pause for several hours |
ileocecal valve |
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once food reaches the ileocecal valve, it waits until after the next meal where a __ is generated to force cyme to move through the ileocecal valve into the large intestine |
gastroieal reflex |
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functions in the reabsorption of water and electrolytes form the cyme |
proximal colon |
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is the storage area for fecal material |
distal colon |
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explain the mixing movement of the large intestine |
large areas of localized contractions occur as circular muscle and longitudinal muscle contract to cause LI to bulge outward into baglike sacs called haustrations
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mixing cause __, allows for __ |
fecal mater to be mixed, maximal water and electrolyte reabsobtion |
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it usually takes __ hours for food to move from the ileocecal valve to the transverse colon |
8-15 |
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the propulsive movement of teh large intestine are called __ |
mass movments |
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the mass movement of the LI contract large areas of the colon to move the __ |
fecal matter towards the rectum |
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mass movements last for __ followed by a __ then reoccur |
2-3 min, 30 sec pause |
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mass movements are associated with __, __, and __ |
rising in the morning, eating, preceding and in association with defecation |
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how many times per day do mass movements occur? |
10x |
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once the mass movements move fecal material to the rectum, the __ |
urge to defecate is felt |
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triggered by the presence of food in teh stomach and or small intestine, can cause a local reflex to produce mass movments |
gastrocolic and duodenalcolic refelxes |
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usually the rectum is devoid of fecal material. however, during mass movement, feces is moved into teh rectum and stimulates a series of contractions to start the process of __ |
defecation |
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when feces enters the rectum, distention of rectal wall initiates __ that spread through teh __ to intiate peristaltic like waves in the descending colon, sigmoid colon, and rectum, forcing feces towrads teh anus |
afferent signals, myentereic plexus |
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as the peristaltic wave approaches the anus, the __ instictively relaxes. |
internal anal sphincter |
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the internal anal sphincter is under __ control |
autonomic |
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the external anal sphincter is under __ control |
conscious and voluntary |
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the __ is usually weak and won't cause defecation to occur |
intrainsic defecation reflex |
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the weaker intrisinc reflex is fortified by the __ which involves the __ |
parasympathetic defecation reflex, pelvic nerves of the sacral segements of the spinal cord |
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the parasympathetic defecation reflex enhances __ and relaxes the __ |
parastaltic like waves, internal anal sphincter |
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the parasympathetic defecation reflex helps relax the internal anal sphincter but defecation will not occur until the __ |
external anal sphincter is volutarily relaxed |
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what happens to the defecation reflexes if the external anal sphincter is kept contracted? |
it dies out |
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what can re-initiate the defecation reflexes after they have died out |
taking a deep breath then contracting abdominal muscles |
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what effect can spinal cord damage have on defecation reflexes? |
the urge to defecate isn't felt, over distention occurs resulting in megacolon |
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what is the migrating motor complex? |
a housekeeping function that sweeps residual matter out of the stomach and intestines |
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the migrating motor complex occurs in __ min cycles |
100 |
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what are the three phases of the migrating motor complex? |
phase I=quiescence
phase II=irregular contractions, little propulsion
phase II=5-10 min of intense contractions propagating from stomach downward, HIGH LEVELS OF MOTILIN |
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the migrating motor complex is suppressed during __ |
feeding |
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describe gas produced in the stomach |
made of nitrogen and oxygen, causes us to belch, comes from swallowing air |
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explain gas in the small intestine |
small amounts, usually CO2, easily absorbed |
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explain gas in the large intestine |
lots of gas produced by bacteria, foods that cause bacteria growth cause more gas production |
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where does teh odor of flatus come from? |
the oder of feces |
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difficult or lack of teh urge to defecate. caused by diet, conscious effort to inhibit defecation, and pathophysiologic reasons |
constipation |
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the absence of the enteric nervous system in teh colon. interal anal sphincter would have an increase in tone and thus no relaxation of teh sphincter during mass movements. causes an intense dilation of the distal colon and usually this segment has to be removed |
congenital megacolon (hirschsprungs disease) |
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very common complaint of abdominal pain with constipation or diarrhea. may be related to stress but real cause is unknown. |
irritable bowel syndrome |
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an immune reaction in teh small intestine as a reaction to eating gluten. overtime it produces inflammation that damages the small intestines lining preventing absorption of some nutrients. causes weight loss, bloating, and diarreha |
celiac disease |
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similar to celiac disease but don't have the same antibodies or intestinal lesions seen in celiac disease or wheat allergy. present IBS like symptoms. gluten free diet leads to remission of symptoms |
non celiac gluten sensitivity |
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what are the two important kind of neurons that affect the GI system? |
sensory neurons
motor neurons |
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what are the two parts of teh enteric nervous system? |
myenteric and submucosal plexus |
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an important part of the enteric nervous system is that a single neuron can release __ |
more than one mediator |
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Myenteric neurons secrete: stimulatory motor __
inhibitory motor __
ascending and descending interneurons __
sensory neurons __ |
AcH, NO, AcH/5-hydroxytryptamine, substance P |
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submucosal neurons secrete: noncholinergic secretormotor neurons __
cholinergic secretormotor neurons __
Sensory neurons __ |
VIP, AcH, Substance P |
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__, __, and __ stimulate GI contraction while __ and __ inhibit it |
stretch, AcH, parasympathetics, VIP, NO |
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how does VIP and NO cause GI smooth muscle relaxation |
by reducing intracellular Ca |
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receives sensory signals from the gut epithelium and stretch receptors in the gut wall |
submucosal plexus |
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the neurons of the submucosal plexus regulate __ and __ |
cellular secretion, local blood flow |
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what is the main purpose of the submucosal plexus? |
sense the enviornement of lumen and regulate GI blood flow and secretion |
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explain the NT's of the submucosal plexus |
AcH (exitatory for secretion)
VIP (excitatroy for secretion, inhibiotry on vascular smooth muscle [causes vasodilation]) |
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the __ neurons of the enteric nervous sytem receive information from mucosa and muscle, respond to mechanical thermal, osmotic, and chemical stimuli. |
sensory (afferent) |
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the cemoreceptors of the sensroy afferent neurons in teh ENS are sensitive to __, __ and __ while sensory receptors in the muscle respond to __ |
acid, glucose, amino acids, stretch |
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he motor neurons of the ENS control __ and __ |
GI motility and secretion |
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the motor neurons act __ on may effector cells |
directly |
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motor neurons of the ENS are predominately __ (using __ and __ NT) but some are __ using __ and __ as NT |
excitatory (AcH, Substance P), inhibitory (VIP, NO) |
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explain the roles of interneurons |
integrate information from sensory to motor neurons
can be inhibitory or excitatory |
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how can sympathetics affect the blood supply to the gut? |
contrcits blood vessels to redirect it to vital organs |
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explain the PNS and SNS of the gut |
Para: vagus nerve and pelvic nerves (S2-S4)
Sympathetic division (T1-L3) |
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the parasympathetic nerves have __ pre-synaptic neurons synapsing close to the target tissue |
long |
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sympathetics have __ presynaptic neurons and __ postsynaptic neurons with prominent ganglia |
shorter, longer |
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postganglionic para fibers use __ to affect smooth muscle while sympathetics use __ |
AcH, NE |
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explain how the sympathetic nervous sytem affects teh gut |
efferent postganglion neuron--NE--decreased motility, decreased secretion, decreased blood flow |
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explain how the vagus nerve works |
long preganglionic cholinergic fibers synapse on cells of the ENS. affect cells responsible for motility, secretion, and hormone release. NT is usually AcH |
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pelvic nerves is important in the __ |
defecation reflex |
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about __% of vagal fibers are sensory and about _% of fibers ar efferent |
90, 10 |
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sensory vagal fibers transmit information from teh gut to the brain about __, __, __, and __ |
glucose, pH, osmolality, distention |
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what kinds of neurons are involved in defecation? |
sensory afferents, parasympathetics (pelvic nerves), somatic motor neurons (ext anal sphincter) |
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what are four examples of the intrinsic reflexes? |
peristalsis, mixing contractions, secretion, local inhibitory effects |
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which 3 GI reflexes are relayed via teh prevertebral sympathetic ganglion? |
gastrocolic, enterogastric, colonoileal |
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which 3 reflexes are relayed via the spinal cord or brainstem? |
vagovagal reflex, defecation, pain refelx |
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explain the gastrocolic reflex |
from stomach to colon to evacuate the colon
gastrin may contribute
pronounced in infants
exaggerated in IBS |
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explain the enterogastric reflex |
from colon or SI to stomach, inhibits gastric motility and secretions
stimulated by HCL in duodenum (low pH)
shuts off gastrin secretion |
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explain the colonoileal reflex |
colon to ileum
inhibits contents at the ileocecal valve from emptying into the colon |
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what are the four routes of communication between cells in teh GI tract? |
endocrine, paracrine, neurocrine, immune system |
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explain endocrine communication |
slower (hormones need to go through the bloodstream)
affects a wide number of cells simultaneouly
long lasting effects |
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explain neuronal communicatoin |
Fast!
covers long distances rapidly
specific point-point
transient signals |
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explain paracrine communication |
localized action
good for responding to changes in the local enviornment |
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explain the immune communication |
responds to antigenic substances or pathogenic mirco-organisms
muscosa is targeted site |
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neurohumoral regulation is mediated by __, __, __, and __ |
peptides, AA, lipid mediators, and steroids |
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explain how crosstalk bewteen neurohumoral system works with CCK and the gallbladder |
CCK released by duodenum in response to nutrients, CCK causes gallbladder to contract sending bile into duodenum, causes vago-vagal reactions which causes NO release to loosen sphincter of Oddi |
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all GI hormones are __ |
peptides |
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what are the 4 criteria of peptide hormones? |
released, absorbed inot blood and delivered into target tissue
effect of peptide persists after neural stimulation ceases
if isolated and purified must elicit same response as physiologic stimuli if applied to target tissue
must be identified chemically |
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what are the 5 GI hormones? |
gastrin, CCK, secretin, GIP, motilin |
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__ is the only stomach produced in the stomach under normal circumstances? |
gastrin |
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how do hormones of the GI tract get to its target tissue? |
portal circulation, general circulation, target tissue |
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the presnece of proteins and AA cauases an __ in gastrin, and __ in CCK, and a __ in motilin |
increase, increase, decrease |
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the presence of fatty acids produces a __ in CCK, a ___ in secretin, a __ in GIP, and a __ in motilin |
increase, increase, increase, decrease |
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the presence of glucose causes an __ in GIP and a __ in motilin |
increase, decrease |
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the presence of acid causes a __ in gastrin and a __ in secretin |
decrease, increase |
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neural stimulation causes an __ in gastrin, a __ in CCK, and a __ in motilin |
increase, increase, increase |
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stretch causes a __ in gastrin |
increase |
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peptide release factors cause a __ in CCK |
increase |
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why is acid the key stimulus for secretin secretion? |
secretin causes HCO# to be produced and secreted by teh pancreas |
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gastrin is secreted by teh __ in teh __ |
G cells, antrum of teh stomach |
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gastrin is secreted in response to __ and __ |
distensin of stomach, neura (vagal) stimulation release GRP) |
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gastrin stimulates teh __ in the body of the stomach to secrete HCL |
parietal cells |
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gastrin stimulates ECL cells to release __ |
histamine (increases acid) |
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gastrin may stimulate __ to secrete pepsin |
chief |
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what are teh two forms of gastrin? |
G-17: produced during ingestion of meal and is stimulus for acid secretion
G-34: produced in small quanitities during basal states |
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CCk is released by __ in response to __ |
I cells, fats |
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CCK stimulates __ and __ |
contraction of the gallbladder, relaxation of sphincter of oddi |
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CCK stimulates the pancreas to release __ |
digestive enzymes |
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CCK is considered to be a __ which is an intestinal hromone that decreases gastric secretions and motility |
enterogastrone |
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CCK causes gallbladder __, pancrease __, stomach __, and shpincter of oddi __ |
contraction, acinar secretion, reduced emptying, relaxation |
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CCK A receptors are usually activated by __ |
CCK |
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CCK B receptors are usually activated by __ |
gastrin |
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what was teh first hormone ever identified? |
secretin |
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secretin is released by __ of teh duodenum in response to __ |
duodenum, acid and fats |
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secretin stimulates the secretion of __ from the liver and pancreatic ductule cells |
HCO3 |
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gastric inhibitory peptide (GIP) is secreted by __ in the duodenum and jejunum predominatly in resonse to __ and __ |
K cells, fats and carbs |
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GIP has a negative feedback to __ gastric acid secretion and has a weak affect to __ gastric motility |
inhibt, decrease |
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GIP stimulates the pancreas to release __ |
insulin |
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GIP is an __ hormone, an enteric hormone to stimulate post prandial insulin release |
incretin |
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motilin is secreted by __ of teh duodenal mucosa |
M cells |
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motlin is released during a __, which triggers the __ |
fasted state, migrating motor complex |
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facilitates cholinergic mediated contractile activity and thus stimulates gastric emptying and intsetinal secretion |
motilin |
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directly contracts gut muscle at high contractions |
motilin |
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release of motilin is inhibited by __ |
feeding |
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chrelin is structuarally related to __ |
motilin |
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ghrelin is produced by teh __ of teh stomach, intestine |
X/A |
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ghrelin acts via __ and __ receptors |
motilin, ghrelin |
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ghrelin is released during __ and suppressed during __ |
fasting, eating |
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ghrelin triggers __ |
feeding |
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ghrelin increases plasma __ |
glucose |
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released by L cells in distal ieum and colon inresponse to glucose and fat. inhibits gastric and intestinal motility |
enteroglucagon |
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derived from proglucagon, made by intestinal L cells, inhibits gastric secretion and emptying, stimulates release of insulin |
glucagon like peptide 1 |
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derived from proglucagon, released by cells of pancreatic islets, secreted in resopnse to hypoglycemia, increases circulating glucose concentration by acting on liver to synthesize and release glucose |
glucagon |
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hormone syntesized by teh pancreas, released in response to ingetstion of a meal, may inhibit motilin release, can inhibit pancreatic HCO3 and enzyme secretion |
pancreatic polypeptide |
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a hormone that is secreted in teh distal SI and colon in response to fat, inhibits gastric secretion and emptying ('ileal break'), possible stiety signal along with CCK |
Peptide YY |
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__ are synthesized in cell bodies of neurons and migrate to the axonal ending where they can be released by an action potential |
neurocrine hormones |
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what are the three neurocrine hormones? |
VIP, GRP, enkphalins |
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neurocrine hormone that causes smooth muscle cell relaxation, increase in secretion of intestinal fluid and electrolytes, decrease gastric motlitiy and secretion of HCL, stimulates pancreatic secretions |
VIP |
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a neurocrine hormone that is released by vagal post ganglionic fibers, stimulates the G cells of teh antrum of the stomach to release gastrin |
GRP |
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neurocrine hormones that increase smooth muscle tone and mediate sphincter contraction, increases the transit time of the intersitinal contents and are used in treating diarrhea |
enkephalins |
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released by endocrine cells within the mucosa and diffuse through the extra cellular space or are carried short distances by capillaries to their target cells |
paracrine hormones |
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what are two paracrine hormones? |
somatostatin, histamine |
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paracrine hormone released by D cells in stomach, intestine, and pancreatic islet cells, released in response to glucose, fat, and bile salts in teh intestinal lumen, decreases gastric acid and pepsinogen secretion, inhibits pancreatic secretions |
somatostatin |
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a paracrine hormone that is produced by ECL cells, release is stimulated by gastrin, stimulutates acid secretion by pareital cells |
histamine |
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CCK, gastrin, GIP, secretin, and pancreatic polypeptide are all used as __ hormones after a meal |
endocrine |
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AcH, CCK, GRP, NO, substance P, VIP, and 5 hydroxytryptamine are all concidered __ hormones after a meal |
neurocrine |
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CCK, histamine, 5 hydroxyltramine, and somatostatin are all __ hormones in response to a meal |
paracrine |
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__ is the only hormone that uses all three hormonal responses after a meal |
CCK |
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what is the source, stimuli for release, and main action for gastrin |
Souce: G cells
stimuli: peptides, AA, neural (GRP, vagal)
action: HCL secretion, pareital cells growth |
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what is the source, stimuli for release, and main action for CCK? |
source: I cells in duodenum and Jejunum
stimului: CCK-RP, fatty acids, AA
actions; pancreatic enzyme secretion, gallbladder contraction |
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what is the source, stimuli for release, and main action for secretin |
source: S cells in duodenum and jejunum
stimuli: luminal pH<4
action: ductal secertion in pancreas of HCO3 and bile ducts |
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what is the source, stimuli for release, and main action for somatostatin |
source: D cells, nerves
stimuli; fat, protein, low pH
action: decreased acid, enxyme secreiton, inhibits gastrin |
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when non beta cell tumors of teh pancreas or duodenum increase gastrin production, lots of HCL, decreases ability of liver and pancreas to neurtalize acid in gut causing ucerations. decreases abilty to absorb digested proudcts due to gut wall dmage. increased fat in stools (stetorrhea) |
zollinger-ellison syndrome (gastrinoma) |
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what are 8 functions of salivary secretions? |
formation of a bolus for swallowing
initiation of starch digestion
facilitates taste/primes stomach
cleasnes mouth
growth factor production
Ca and PO4 for tooth health
HCO3 to neutralize stomach acid
aids in speach |
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you produce __ ml of saliva a day |
800-1500 |
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what are the principal glands of salivary secretion and what is the percentage of secretion? |
parotid gland (25%)
submandubular gland (70%
sublingual gland (5%) |
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explain the structure of the salivary duct |
acinar cells produce ptyalin, mucus, and extracellular fluid, myoepithelial cells around acinar cells contract to propel secreions out of duct, strated ductular cells are polarized to allow for ion movment |
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explain the ion movement that occurs in teh striated ductular cells |
Na active absorption
Cl passive absorption
K active secretion
HCO3 secertion |
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although ions can move across the salivary ductal cells, H2O cannot. why? |
they have tight junctions between cells keeping water in the lumen |
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Components of saliva: mucins do __, amylase does __, lipase does __, lysozyme is __, IgA is __ and nerve growth factor and epidermal growth factor are __ |
lubrication, digestion of starch, digestion of fat, antibacterial, immune protection, protective |
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|
explain the control of salivary production |
conditioned reflexes, smell, taste, pressure, and nausea increase
fatigue, sleep, fear, and dehydration decrease
both affect teh salivary nucleus in teh medulla
activate parasympathetics to release AcH causing an increase in Ca in salivary glands to produce saliva
sympathetics use NE to slightly trigger cAMP to stimulate the glands |
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the fundus and body of tehs tomach are key sites of __ production |
acid |
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the fundus and body of teh stomach contain __% of the stomachs gastric glands. these glands are located in __ |
75%, gastric pits |
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what are the 5 kinds of cells types found in teh gastric pits? |
mucus producing cells, parietal cells, D cells, ECL cells, chief cells |
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what do parietal cells secrete? |
HCL and intrinsic factor |
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what is the function of intrinsic factor? |
vitamin B12 absorption |
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what do cheif cells secrete? |
pepsinogen |
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what do surface mucous cells secrete? |
mucus, bicarbonate, trefoil factors |
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what do ECL cells secrete? |
histamine |
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what do G cells secrete? |
gastrin |
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what do D cells secrete? |
somatostatine |
|
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explain the three phases of gastric acid secretion in response to a meal |
cephalic: thinking about food, neuronal input tells stomach to release hormones
gastric: stretching amplifies secretion (longest phase)
intestinal: signals start to wind down secretion |
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what nerve delivers the message to the stomach during the cehpalic phase of gastric secretion? |
the vagus nerve |
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during the cephalic stage of gastric secretion , how does the vagus nerve affect secretory cells? |
AcH affects chief, parietal, and ECL cells as well as G cells |
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parietal cells of the stomach which produce HCL are stimulated by __, __, and __ |
G cells via the blood, ECL cells (via histamine), and parietal cells via AcH from vagus nerve |
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explain the secretion of HCL |
gastrin, histamine, and AcH stimulate apical H/K atpase
H/K atpase actively transports H+ into lumen against pH gradient
Cl is secreted by electron channels to form HCL
H+ ions produced via reaction of H2O and CO2
HCO3 is transported out |
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what are three ways to reduce acid in teh stomach? |
add bicarbonate, inhibit H2 receptors on parietal cells, block H-K proton pump |
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pancreatic enzymes are secreted in an __ state |
inactive |
|
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how does secretion from acinar cells work? |
VIP, secretin increase cAMP, CCK, GRP, ACh increase Ca
cause fusion of granules to apical membrane to release stored enzymes |
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what stimulates S cells to secrete secretin? |
pH<4.5 |
|
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secretin causes pancreatic ducts to release __ to __ |
HCO3, increase pH |
|
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what is the total intake of fluid and the total excreted in the stool? |
total in: 9000 ml
excreted in stool: 100 ml |
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intestines have a large __ to aid in absorption |
surface area |
|
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__78% of fluid is abosrbed in the __, 21% is in the __ |
small intestine, large intestine |
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what are the general rules for absorption and secretion in the intestine? |
villus cells are usually absorpative
crypt cells tend to be secretory |
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absorptive mechanisms in teh GI tract usually rely on __ movment |
Na |
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secretory mechanisms of teh GI tract generally rely on __ movment |
Cl |
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__ transport drives most aborption in the GI tract |
active |
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what are 5 characteristics of active transport pathways of the GI system? |
bring ions uphill against gradients
requires ATP
can be used at low lumenal concentrations
demonstrate staturable kinetics
demonstates ionic specificity
|
|
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what three kind of transporters are used in GI absorption |
pumps (atpases)
channels
carriers |
|
|
what are three mechanisms of Na absoprtion? |
Na coupled glucose transport
ENaC mediated Na absorption
Electroneutral Na absorption |
|
|
explain the Na coupled glucose transporter |
in SI
SGLT1 on apical membrane brings glucose into cell
GLUT 2 on basolateral membrane brings glucose into blood
allows paracellular Cl absorption and passive water flow |
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explain ENaC mediated Na absorption |
mostly in colon
paracellular Cl absroption
very little glucose |
|
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explain electroneutral Na absorption |
Na coupled to Cl absorption
no nutrients required
can occur during fasting state |
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what are the 5 methods of absorption and 2 methods of secretion in teh smal intestine? |
Na coupled nutrient, electorneurtal NaCl, H+ coupled nutrient, Na coupled bile acid, and Ca andiron absorption
HCO3 and Cl secretion |
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explain teh three absorption and 1 secretion processes in teh colon |
electrogenic Na, eltroneurtral NaCl, short chain fatty acid abosrption
Cl secretion
No nutrient coupled uptake |
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what two factors that affect absorption? |
movement across teh wall (SA, cell function)
speed of movement through the tube (high motility=less time to uptake fluid) |
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|
explain chloride secretion |
in SI and colon
CFTR is main channel
stimulated by cAMP
electogenic (Na and water follow)
uses NKCC channel |
|
|
explain bicarbonate secretion |
prominent in proximal duodenum
generated intracellularly/taken from bloodstream
primary stimulus is acid |
|
|
what causes secretory diarrhea? |
irreversible activation of Gs increases cAMP, stimulates Cl secretion adn inhbiits electroneurtral NaCl absroption, water follows |
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|
a mixture of large glucose polymers |
starch |
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|
amylose is __% of starch
amylopectin is __% of starch |
25, 75 |
|
|
what are the two disaccharides? |
sucrose (glucose+fructose)
lactose (glucose+galactose) |
|
|
what are two monosaccharides |
glucose, fructose |
|
|
the intestine can only transport __ meaning __ |
monosaccharides, starch must be digested |
|
|
what are the two phases of carb digestion |
luminal, brush-border digestion |
|
|
what drives luminal digestion |
amylase |
|
|
what are the two forms of amylase? |
salivary (inativated by low pH)
pancreatic (secreted 15-30 min to digest all CHO) |
|
|
__ chops polysaccarchids into small units but does not cleave the __ bond |
amylase, alpha 1, 6 bond |
|
|
brush border enzymes in the SI are efficient b/c of the __ of hydrolytic enzymes to transport pathways |
proximity |
|
|
how is sucrose digested by the brush border enzymes? |
cleaved by sucrase into glucose and fructose |
|
|
how is lactose digested |
gleaved by lactase into glucose and galactose |
|
|
lactase activity is inhibited by __ |
glucose |
|
|
what transporters take up monsaccharides? |
SGLT1, GLUT5, GLUT2 |
|
|
mediates secondary active transport of glucose and galactose across brush border
cotransport of Na and monsaccharides
Na reguired for glucose bidning
preent in teh membrane as a homotetramer
missense mutations result in glucose-galactose malabsorption |
SGLT1 |
|
|
brush border facilitatied transport for fructose, Na independent |
GLUT 5 |
|
|
Basolateral facilitated diffusion pathway for glucose to exit the cell, Na independet |
GLUT2 |
|
|
how does protein assimilation differ from carbohydrates? |
oligomers can be transported into enterocytes
cytosolic digestions occur |
|
|
what are the three kinds of amino acids |
neutral, basic, and acidic |
|
|
gastric proteolysis is mediated by __ |
pepsins |
|
|
pepsins are stored and secreted by __ cells as inactive precursors |
chief |
|
|
pepsins are inactivated at a pH of __ |
>4.5 |
|
|
what are the two kinds of pancreatic peptidases? |
endopeptidase
ectopeptidase/carboxypeptidase |
|
|
pancreatic peptidases are secreted as __ |
inactive precursors |
|
|
what is the intial step of activatino of peptidases? |
clevage of N terminal hexapdptide from trypsinogen |
|
|
trypsin converts trypsinogen to __, chymotrypsinogen to __, proelastase to __, procarboxypeptidase A to __ and procarboxypeptidase B to __ |
trypisn, chymotrypsin, elastase, carboxypeptidase A, carboxypeptidase B |
|
|
trypsin, chymotrypsin, and elastase are all __ |
endopeptidase |
|
|
carboxypepsidase A and B are __ |
ectopeptidases |
|
|
explain the pathways of luminal proteolysis |
large peptides--trypsin, chymotrypsin, elastase--basic AA--carboxypepsidase B--free AA and small peptides
large peptides--trypsin, chymotrypsin, elastase--neurtal AA--carboxypeptidase A--free AA and small peptides |
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|
luminal proteolysis is __. it does __% of small oligopeptides and __% free neutral and basic AA |
incomplete, 60-70, 30 |
|
|
brush border proteolysis is expressed by __, not __ enterocytes |
villus, crypt |
|
|
this tansporter takes in broad ranges of substrates (including some peptide like drugs)
certain AA are more efficiently abosorbed when presented as dipeptides than individually
|
PEPT 1 |
|
|
caused by defects of neutral AA transport |
hartnup disease |
|
|
caused by defects of basic AA transport |
cystinuria |
|
|
what are three enzymes used in cytosolic digestion? |
amino tripeptidase
amino dipeptidase
Xaa-Pro dipeptidase |
|
|
dipeptides containing __ and __ are relatively resistant to hydrolysis and are manly taken up in peptide form |
glycine, proline |
|
|
explain how cholesterol is made water soluble by bile acids to be disolved in the blodstream |
cholesterol is hydoxylized in the liver made water soluble by primary bile acids then less water soluble in teh distal SI and colon by secondary bile acids |
|
|
explain how bile acids are conjugated into bile salts |
conjugated into glycine or taurine
increases water solubility |
|
|
__ contains bile acids, lecthin, phosphatidycholine, cholesterol, bilirubin, and HCO3 |
bile |
|
|
what are the three functions of bile |
emulsify's fat (increases SA for lipase)
absorption of fats by forming micelles
excretion of bilirubin and cholesterol |
|
|
how is bile concentrated in the bladder? |
Na reabsorption by Na-K atpase drives secondary absorption of other ions and water
bile becomes slightly acidic
gets higher concentration of Ca in gallbadder than liver bile |
|
|
The acidity in bile prenvents Ca binding to HCO3 and creating__ |
gallstones |
|
|
what are the two kinds of gallstones? |
cholesterol stones (most common)
pigment stones (bilirubin) |
|
|
what are the three F's that describe the population at risk for gallstones |
fat, female, over fourty |
|
|
the liver secretes __g of bile acids a day |
12-36 |
|
|
liver synthesizes __ mg/day of bile |
600 |
|
|
bile acids recirculate __x a day which is important because recycling is more important b/c bile acids solubilze fat by mass action |
4-12 |
|
|
in fat assimilation __ are broken down into __, which are broken down into __ |
triglycerides, monoglycerides, fatty acids |
|
|
most dietary fat is in the form of __ |
triglycerides |
|
|
digestion (lypolysis) begins in the stomach but only about __% |
10-30 |
|
|
after the stomach, fat digestion and solubilization continues in teh __ |
intestines |
|
|
small aggregates of mixed lipids and bile acids suspended within teh ingesta. as ingesta are mixed, they bump into teh brush border of SI enterocytes and lipids including monoglycerlides and fatty acids are taken up into epithelia cells |
micelles |
|
|
lipids are taken up by teh endoplasmic reticulum and reassembeled into __ for export |
chylomicrons |
|
|
explain how chylomicrons are taken into the blood |
chylomicrons pinocytosed onto basolateral border of enterocyte
absorbed inot lacteal of illus and transported into lymphatic system
lympatics drain into blood via thoracic duct |
|
|
explain how fat is taken from the intestine to the blood stream |
lipids (monoglycerides and fatty acids) attach to bile acids/salts form micelles--micelles broken down into chylomicrons via brush borders enzymes--chylomicrons enter lacteals, go to toracid duct which drains into venous angle |
