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197 Cards in this Set

  • Front
  • Back
How does the parasympathetic pathway innervate the GI?
stimulates activity
Whast is the vagovagal reflex?
information from receptors in mucosa and smooth muscle relayed to CNS via vagus afferents, then efferents from vagus are sent back to GI tract
What does the sympathetic pathway do?
inhibits activity; usually fibers synapse outside the GI tract
What are the myenteric and submucosal plexuses part of?
intrinsic/enteric innervation system; relay info via extrinsic system
what are neurocrines?
synthesized in cell bodies of neurons nadn released by AP's
where is gastrin secreted from
G cells in stomach
what is gastrin released in response to
peptides and amino acids from protein digestion, distension of the stomach and vagal stimulation
what does gastrin stimulate
HCl secretion
what inhibits gastrin secretion
acid in stomach
what is zollinger-ellison syndrome
people who hypersecrete gastrin and develop ulcers, diarrhea and steatorrhea
where is CCK released from
I cells of small intestine in response to peptides, aa, fatty acids and monoglycerides
what does CCK stimulate
gallbladder contraction and pancreatic enzyme secretion and also potentiates HCO3 secretin with secretin
what does CCK inhibit
gastric emptying
what does secretin stimulate
HCO3 and H2O secretion in pancreas and liver; also increases bile production
what does secretin inhibit
gastric acid secretion
where is secretin released from
S cells of small intestine in response to acid
what does gastric inhibitory peptide stimulate
insulin release; released in response to fat, protein and carbs
what is gastric inhibitory peptide stimulated by
proximal small intestine
when is motilin released
every 90 minutes during fasting
what does motilin stimulate
migrating myoelectric complex in stomach and small intestine
When is somatostatin stimulated?
secreted in response to acid in lumen
what does somatostatin inhibit?
gastric acid secretion and release of gastrin and release of all GI hormones
what is histamine's function
increase gastric acid secretion directly and by potentiating effects of gastrin and Ach
whats the function of vasoactive intestinal peptide?
relaxation of smooth muscle and stimulates intestinal and pancreatic secretion
what are the role of enkephalins
stimulate contraction of GI smooth muscle and inhibit intestinal secretion of fluid and electrolyte
what are the neurocrines
VIP, GRP and enkephalins; all released from nerves in mucosa
what are slow waves
periodic changes in resting membrane potential of smooth muscle cells
what generates a slow wave
intersitial cells of Cajal
are slow waves action potentials
no but they do determine the pattern of AP's
what are the two phases of slow waves
upstroke and plateau phase
when can contraction occur during a slow wave
when plateau phase exceeds threshold
what happens when threshold is reached
voltage gated Ca channels open and Ca comes in causing an AP
what do AP's do to slow waves
increase strength and duration of contraction
can contractions occur in the absence of action potentials?
only in the stomach
how can neural or hormonal input influence contraction
nerves increase probablity that membrane potential will cross threshold but will not affect frequency
what sets max frequency for contraction for any part of the GIU
frequency of slow waves
can you have contractions without slow waves
no but can have slow waves without contractions
3 functions of salivary secretion
digestion of starch and fat, lubrication and protection from bacteria
3 major glands
parotid, sublingual and submandibular
which one contributes to salivation the most
what is the acinus of a duct
blind end, lined with acinar cells that secrete initial saliva
what connects acinus and striated duct
intercalated duct
what is the striated duct
modifies inorganic composition of saliva
specialized contractile cells
myoepithelial cells
what contols saliva
autonomic nervous system, parasympatheic and sympathetic nerves increase saliva
which one, PSNS or SNS provides stronger input for saliva release
what is the role of PSNS in saliva realease
increase transport processes of acinar and ductal cells, stimulates vasodilation of blood vessels and stimulates glandular metabolism and growth
what is the role of SNS on saliva secretion
transiently increases production and growth of salivary glands, contraction of myoepithelial and constriction
what would lesioning PSNS nerves do to salivary glands
atrophy them, SNS would have little effect
what increases production of saliva
food, smells, conditioned reflexes and nausea
what decreases production of saliva?
sleep, fatiuge, dehydration, fear and anticholingeric drugs
what is saliva composed of
water, electrolytes and organic compounds, bactericidal compounds; acidic pH
what proteins are in saliva
mucin-lubrication and protection
what is the ionic composition of saliva
ultrafiltrate of plasma and hypotonic to plasma
how do the striated ducts modifiy the ionic composition of fluid
reabsorb Na and Cl, secrete K and HCO3 into plasma
how does flow rate affect concentrations
higher flow rate= less time for reabsorbtion and saliva more isotonic
what ion is increased with increasing flow rate
HCO3 (secretion into plasma) because its secretion is stimlulated when salivation stimulated
when does flow rate increase
what is xerostomia
lack of salivary secretion
what can cause xerostomia
chronic infection of buccal mucoas and dental caries, antidepressants and Sjogrens
what are the 2 phases of swallowing
oral (voluntary) and pharyngeanl (involuntary)
what initates the oral phase of swallowing
collecting bolus of food and forcing it into oropharynx by pushing it up and back against hard palate
what is the process of the pharyngeal phase of swallowing
1. nasopharynx closed by soft palate and breating inhibited
2. laryngeal muscles contract to close glottis and elevate larynx
3. peristalsis begins to propel food toward esophagus
4. upper esophageal sphincter relaxes and allows contraction of contstrictor muscles in pharynx to move mater into esophagus
difficulty in swallowing; caused by neurological disorders
structure of esophagus
upper 1/3 striated muscle, lower 1/2 smooth muscle
function of upper esophageal sphincter
separates esophagus from oral cavity and prevents entry of air
function of lower esophageal sphincter
separates esophagus from stomach and prevents entry of gastric acid
what initates primary peristaltic contraction
swallowing, it creates a zone of increased pressure behind bolus
what happens as bolus reaches LES
sphincter relaxes, allows bolus into stomach and then contracts preventing reflux
what initiates the secondary peristaltic contraction
presence of food in esophagus which stretches mechanical receptors, continues until all food is removed
what is GERD caused by
decreased tone of LES-reflux of stomach acid
what does GERD cause
heartburn and esophagitis
how is GERD treated
lifestyle changes, medications, surgery
what will long term exposure to acid lead to
Barrett's esophagus causing metaplasia
what is achalasia
neuromuscular disorder of lower 2/3 of esophagus leading to absence of peristalsis and failure of LES to relax
what is the outcome of achalasia
food accumulates in esophagus and takes hours to enter stomach
what do patients with achalasia experience
dysphagia, regurgitation of ingested food and weight loss
how is achalasia treated
drugs, surgery to relax LES and endoscope
what causes bleching (eructation)
air swallowed during eating or drinking; when LES relaxes during swallowing, air/gas enters esophagus and is regurgitated
what are the 2 function areas of the stomach and their functions
orad- receives ingested meal
caudad- responsible for contractions that mix food and propel it into duodenum
receptive relaxation
food enters the orad region and stomach opens and allows food in without increasing pressure; mediated by vagovagal reflex
when does mixing occur in the stomach
presence of food causes caudad stomach to increase contractions therefore mixing food with gastric acids
food mixed into a pasty consistency
where do peristaltic contractions originate in the stomach
midstomach and proceed caudally; velocity and force of contraction increases as moved distally
where do slow waves originate
in pacemaker near border of orad and caudad
wave of contraction closes antrum and pyloric sphincter before chyme reaches there and this causes chyme to be propelled back into stomach to be mixed
migrating myoelectric complex
contractions that occur every 90 minutes during fasting to clear the stomach of any residual food
what type of foods leave the stomach faster
carbohydrate faster than protein faster than fats
what controls the rate of food leaving the stomach
inversely proportional to pressure in orad stomach; increase pressure longer it takes food to leave stomach (increases during digestive period)
what inhibits gastric emptying
1. high fat or protein digestion products
2. increased distension of orad stomach
3. increased pressure in small intestine
4. decreased frequency and force of peristaltic contractions in caudad
impaired or delayed emptying; produces symptoms of fullness, loss of apppetite and nausea
dumping syndrome
occurs when lower end of small intestine fills too quickly with undigested food from the stomach; usually a result of stomach surgery
oxyntic gland mucosa
region of stomach for secretory function; located in proximal 80% and secretes acid, pepsinogen, intrinsic factor and mucus
pyloric gland mucosa
distal 20% of stomach and secretes gastrin
paritel cells
secrete acid and intrinsic factor
chief cells
secrete pepsinogen
mucous neck cells in oxyntic gland
secrete mucus
gastric juice has 4 components
1. HCl
2. pepsin
3. mucus
4. intrinsic factor
functions of HCl
begins digestion of protein, converts pepsinogen to pepsin and provide optimal pH, kills bacteria that enter stomach
function of pepsin
digests protein; stimulated by vagus and acid
function of mucus
protective coating for stomach and lubricant and barrier between cells and ingested material
what is the soluble form of mucus
mixes with other secretions of glands and lubricates chyme; not present in resting stomach; secreted by mucus neck cells
what secretes insoluble form of mucus
surface epithelial cells in resting stomach in response to chemical or physical irritation
what forms the unstirred layer
insoluble mucus
function of unstirred layer
traps dead cells and forms protective coat; HCO3 also trapped maintaining neutrality of stomach surface
what happens to insoluble mucus
on contact with acid passes into duodenum with chyme
functin of intrinsic factor
necessary for absorption of B12
what does an absence of intrinsic factor lead to
pernicious anemia
function of paritel cells
secrete HCl into lumen of stomach and HCO3 into bloodstream
how is H formed in paritel cells
from dissociation of water; it is secreted into the lumen in exchange for K
what enzyme forms HCO3
carbonic anhydrase
what is exchanged for HCO3
Cl enters the cell and HCO3 leaves
alkaline tide
created by HCO3 in venous blood; increases pH; presence of so much HCO3 in blood by paritel cells
what happens at low(basal) rates?
gastric juice primarily NaCl from nonparitel secretion
What 3 things stimulate acid secretion
all 3 required for production
how does Ach stimulate acid secretion
binds to muscarinic receptors, activates phospholipase C and causes release of Ca
how does histamine cause acid release
binds to H2 receptors on paritel cells and activates adenylate cyclase
how does gastrin stimulate gastrin release
binds to gastrin receptors on paritel cells, activates phospholipase C and causes release of Ca
what is potentiation?
when response to simulataneous administration of 2 stimulants greater than sum of responses to either agent given alone
what potentiates the actions of gastrin and Ach
what is the function of histamine receptor blockers
can inhibit acid secretion because they block action of histamine therefore blocking action of Ach and gastrin
what does Ach potentiate
histamine and gastrin
what stimulates the synthesis of histamine
gastrin and Ach but gastrin more
what inhibits acid secretion in the stomach
low pH and chyme in duodenum
what hormone inhibits acid secretion when pH gets too low in the stomach
what occurs in the basal phase of acid secretion
occurs in absence of all gastric stimulation, circadian rhythm (highest at night)
what initates the cephalic phase
thought, sight, taste and smell of food
how does vagus nerve increase acid secretion during the cephalic phase
Ach directly stimulates paritel cells and Ach causes release of GRP
what initates the gastric phase of acid secretion
entry of food into stomach
during what phase is the largest amount of gastrin secreted
gastric phase
how does food entering the stomach cause acid release
1. stomach distends
2. stretch receptors activated
3. initate vagovagal reflexes
4. gastrin release stimulated and acid secretion stimulated via Ach
what nutrient stimulates gastric secretion
what other substances stimulate acid secretion
Ca and caffeine
what inhibits secretion of acid in the stomach
acid itself
what initates the intestinal phase
presence of protein digestion products in duodenum; duodenum secretes gastrin which then stimulates acid secretion
when does a gastric ulcer occur
when protective barrier of stomach breaks down, injuring of mucosa by acid
what are more common, duodenal or gastric ulcers
when does pain during eating occur
gastric ulcers
what is the pathophysiology of duodenal ulcers
too much acid, gastrin and pepsin; no control mechanism for acid production
what can cause ulcers
H. pylori, NSAIDS and alchol
what is the Tx for ulcers
proton-pump inhibitors, antibiotics and pepto-bismol
what is another word for vomiting
definition of vomiting
forceful expulsion of gasric and intestinal contents through mouth
where does vomiting begin?
distal small intestine as a wave of reverse or anti-peristalsis
what is retching
involves all involunatary motions of vomiting without production of vomitus
what accompanies vomiting
increased salivation, sweating, rapid breathing and irregular heartbeat
where is the vomiting center
what activates the afferents for vomiting
tickling back of throat, distension of stomach or duodenum, vestibular stimulation and painful injury to genitourinary tract
what does stimulation of second separate medullary area lead to
retching without vomiting
what does direct activation of the vomiting center cause
vomiting without nausea or retching
where is teh chemoreceptor trigger zone
fourth ventricle
what activates the CTZ?
emetics, radiation and motion sickness
what are some effects of protracted vomiting
metabolic alkalosis
where do the major parts of digestion occur
duodenum and jejunum
where are the fold of Kerckring?
longitudinal folds on the surface of the small intestin
purpose of villi
increase surface area
another name for microvilli
brush border
where are the crypts located
project down into surface at base of each villus; 3 crypts/villus
3 cells of the smaill intestin
enterocytes, goblet cells and crypt cells
function of enterocytes
digestion, absorption and secretion
function of goblet cells
secrete mucus; interspersed with enterocytes
function of crypt cells
secrete fluids and electrolytes
function of small intestine
mix chyme with digestive juices and bile to facilitate digestion and absorption
types of contraction in the small intestine
segmentation, peristalitic and migrating motility complex
most common type of contraction in small intestin
how does segmentation work
smooth muscle contracts pushing chyme toward stomach and colon, when muscle relaxes chyme returns to original segment to mix with digestive juices
where is the higher frequency of contractions
proximal intestine to propel it downward toward colon
purpose of peristalsis in small intestine
propel chyme down small intestine; only moves short distance
how often does the migrating motility complex occur
every 90 minutes to clear remaining chyme from small intestine
do intestinal slow waves trigger contraction by themselves or through spike potentials
through spike potentials
what is the strength of the contraction proportional to
frequency of spikes; greater slow wave amplitude, greater frequency therefore greater contraction
does the frequency of slow waves increase distally
no, decreases
what affects the motility of small intestine
higher centers of nervous systme
peristaltic reflex
contraction that moves intestinal contents along small intestine; initated by chyme
intestinointestinal reflex
overdistension of one segement inhibits contractile activity in the rest of the intestine; prevents movement of material into already distended segment of bowel
gastroileal reflex
gastric secretion and emptying triggers increased peristalsis in ileum causing relaxtion of ileocecal sphincter and movement of ileal contents into large intestine
what do acinar cells secrete
petidases, lipases and amylases
what do ductule cells secrete
pancreatic juice containing high HCO3
is pancreatic juice alwasy isotonic with plasma
what is higher in plasma
what is lower in plasma
Cl and K is equal
what is pancreatic juice composed of at lowest flow rates
Na and Cl
what is pancreatic juice composed of at high flow rates
Na and HCO3
what enzymes are secreted in the active form
lipase and amylase
what are pancreatic proteases
trypsin and chymotrypsin which are secreted as inactive precursors
why is trypsin inhibitor secreted
to protect pancreas from autodigestion
what neurotransmitter acts on acinar and ductule cells
Ach during gastric and cephalic phase
what stimulates the intestinal phase in the small intestine
acid and fat and protein digestion products in duodenum
where is acid released from in the small intestine
S cells in the duodenum
where does secretin act on the small intestin
acts on ductule cells to increase HCO3 release
what triggers CCK release from I cells
fata and protein digestion products
what is CCK's function in the small intestin
acts on acinar cells to increase enzyme secretion
what else stimulates enzyme secretion from the pancreas
vagovagal reflex that was initated by acid and fat and protein products
what potentiates teh effect of secretin
CCk and Ach
what causes pancreatitis
chronic alcoholism or gallstones
acute symptoms fo pancreatitis
severe abdominal pain, swollen and tender abdomen, nausea and vomiting, diarrhea and fever
what are the serum amylase and lipase levels in pancreatitis
greatly elevated