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157 Cards in this Set

  • Front
  • Back
what begins starch digestion in the mouth?
alpha amylase
what begins lipid digestion in the mouth?
lingual lipase
what is a glycoprotein produced by salivary glands that lubricates food to make it easier to swallow?
mucin
how much saliva is made in one day?
1 L
what is a converting enzyme in saliva that results in bradykinin (a vasodilator)
Kallikrein
what happens to saliva as it moves through the ductal system due to ductal cells?
goes from being isotonic to hypotonic
which electrolytes have a higher concentration in saliva? which ions have a lower concentration?
High in K and HCO3
Low Na and Cl
what produces the initial isotonic saliva?
acinar cells
the electrolyte compostition of saliva is initially isotonic by comparison to what?
plasma
what modifies the composition of saliva?
ductal cells
what is the relationship between ductal cells and water?
ductal cells are impermeable to water (only the ions move via membrane transporters)
what is saliva comprised of?
water, enzymes (amylase and lipase), ions (HCO3 and K), mucus, IgA, lysozyme and kallikrein
what are the functions of the components of saliva?
to aid in digestion of starch and lipids, dilution/buffering and lubrication
what factors stimulate salivary flow?
food (sight, smell, taste), smell, nausea and conditioning, sour foods (basically acid, or H+)
what factors inhibit salivary flow?
dehydration, fear, sleep, and anticholinergic drugs (atropine)
levels of which ions increase with salivary flow? which decrease?
Na and Cl (bc there is less contact time and therefore less Na and Cl pulled out) and HCO3 (because its under separate regulation)
K is reduced (same reason)
how is salivary secretion controlled?
strictly under neuro control
is parasympathetic or sympathetic control more dominant in regards to salivary flow?
parasymp
what do parietal cells produce?
hydrochloric acid and intrinsic factor
what is necessary for Vit B12 transport to the ileum, where it is absorbed?
intrinsic factor
what is the only essential secretion of gastric juice?
intrinsic factor
what converts pepsinogen into pepsin?
HCl
which cells produce pepsinogen?
chief cells
what is the importance of mucus and HCO3 in gastric juice?
protects lining
where are oxyntic glands found?
in the body of the stomach
where are pyloric glands found?
in the antrum of the stomach
what is significant about the production of gastrin by G cells?
gastrin goes into the circulation, not the ducts
how is HCl secreted from the parietal cell?
via a proton pump (exchanges K to maintain electroneutrality)
what happens to HCO3 once its pumped out of the parietal cell?
goes into bloodflow (results in alkaline tide)
what is the "alkaline tide"?
rise in blood pH following a meal. occurs when HCO3 moves into the blood via the Cl-HCO3 exchanger along the basolateral membrane.
which cell type releases histamine?
ECL cells
which factors stimulate HCl secretion from parietal cells?
ACh, gastrin, and histamine
which factors inhibit HCl secretion from parietal cells?
somatostatin and prostaglandins
how do somatostatin and prostaglandins work?
bind to parietal cells via inhibitory G protein that inactivates adenylyl cyclase, which causes cAMP levels to fall.
Somatostatin also works indirectly to inhibit both histamine and gastrin release.
why is a side effect NSAIDs an increase in acid secretion that could lead to ulcers
they inhibit prostaglandin synthesis
which stage of gastric secretion comprises 30% of HCl secretion? 60%?
30% - cephalic
60% - gastric
which phase of gastric secretion is triggered by smell, taste, chewing, swallowing and conditioned reflexes?
cephalic
what are the 2 mechanisms that promote HCl during the cephalic phase of gastric secretion?
1) direct stimulation of parietal cells by the vagus nerve
2) indirect stimulation of parietal cells by gastrin
which phase of gastric secretion is triggered by distention fo the stomach and the presence of breakdown products of proteins (amino acids and sm peptides)
gastric phase
what are the 4 mechanisms of the gastric phase of gastric secretion?
1) direct stimulation by the vagus nerve
2) indirect stimulation by gastrin
3) local reflexes caused by the distention of the antrum promote gastrin release
4) the presence of amino acids/ small peptides promoting gastrin release.
how is the inhibition of HCl accomplished?
decreased pH of the gastric contents inhibits the secretion of gastrin
also by prostaglandins and somatostatins
lack of distention stimuli
What is the major stimulus for decreasing HCl secretion?
Low pH, as buffering chyme moves out of the stomach, is the major inhibitory stimulus for decreased acid secretion. Low pH will inhibit gastrin secretion; direct effect on G cells.
what makes pepsin inactive?
higher pH
what are protective factors affecting peptic ulcer dz?
HCO3 and mucus (on lining)
prostaglandins (dec acid secretion from parietal cells)
mucosal blood flow (inc secretion of HCO3)
growth factors (inc mucosal lining)
damaging factors affecting peptic ulcer dz?
H and pepsin
H. pylori
NSAIDs
stress
smoking
alcohol
caffiene
what causes gastric ulcers? what happens to acid secretion?
H. pylori, acid secretion dec
what is the most common type of ulcer? what is it caused by?
duodenal ulcers. caused by H. pylori.
is acid secretion increased or decreased in duodenal ulcers?
increased.
what happens when H. pylori colonizes gastric mucosa in the duodenum?
inhibits somatostatin secretion from D cells; increases gastrin and H secretion; infection spreads and inhibits duodenal HCO3 secretion
how does H. pylori cause damaging effects in gastric ulcers?
releases cytotoxins that breakdown the protective barrier of the mucus and epithelium
which cells secrete somatostatin?
D cells
what stimulates chief cells to secrete pepsinogen?
vagal or H+ stimulation
what secretes most of the enzymes required for digestion?
pancreas
is pancreatic juice hypotonic or isotonic to the blood?
isotonic
what is secreted into the lumen of the pancreas by duct cells? into the blood stream?
HCO3 into lumen, acid secreted out of basolateral membrane and picked up by blood
what is not affected by flow rate of pancreatic juice?
Na or K
increased flow rate of pancreatic juice results in higher _____? lower _____?
Higher HCO3 and lower Cl
what is CCKs role in regard to pancreatic juice?
regulation. amino acids, sm peptides and fatty acids stimulate I cells to release CCK.
Which amino acids have the greatest impact on CCK secretion?
Phenylalanine, methionine and tryptophan
what is the overall function of bile?
emulsifies lipids and renders them soluble so that they can be absorbed
what produces bile? Where is it stored?
hepatocytes; gallbladder
where are the primary bile acids produced?
liver
what composes about 50% of the organic component of bile?
bile salts
What are the bile acids produced from?
cholesterol
what are the two primary acids secreted by the liver?
cholic acid and chenodeoxycholic acid
what converts some primary bile acids into secondary bile acids?
intestinal bacteria
what are the 2 secondary bile acids?
deoxycholic acid and lithocholic acid
what does the liver conjugate bile acids with to increase solubility?
glycine or taurine
what is bile comprised of?
bile salts, cholesterol, phospholipids, bile pigments, ions and water
what are bile salts responsible for?
solubilizing dietary lipids by emulsifying them and helping to form micelles.
Cholesterol and phospholipids also participate in the formation micelles
what composes 2% of bile and is the major bile pigment. Is derived from the breakdown of RBC in the spleen.
bilirubin
what is a major consequence of ileal resection?
steatorrhea
what is inhibited by bile salts traveling back to the liver in enterohepatic circulation?
Cholesterol 7a-hydroxylase
what stimulates the secretion of bile salts in enterohepatic circulation?
Choleretic effect
Smooth muscle of the GI tract in which the cells are electrically coupled via gap junctions?
Unitary smooth muscle
What are phasic contractions?
Periodic contractions followed by relaxation.
What are tonic contractions?
Maintain a constant level of contraction or tone w/o regular periods of relaxation.
What are slow waves?
Not action potientials, but oscillating depolarization and repolarization.
Where do slow waves originate?
In the interstitial cells of Cajal, which are abundant in the myenteric plexus.
About how much fluid/day is added to the GI tract?
about 9L
What are the sources of fluid added to the GI tract?
Diet: about 2 L
Saliva, gastric juices, pancreatic juices, bile and small intestines: about 7L
how much fluid is lost in the feces?
about 100-200 mL are excreted in feces
Where does most absorption of fluid occur in the GI tract?
in the small intestine
(also some in the colon)
what part of the GI tract secretes and absorbs fluid?
small intestine
what accounts for the large amount of absorption and secretion in the small intestine?
the tight junctions are "leaky" or not tight fitting
why is there less fluid absorption in the colon?
the tight junctions are very tightly fitted
What is the term used to describe when fluids and substances move between cells
paracellular movement
term for: as solutes are absorbed across the epithelial cells, water follows the solute movement
isosmotic absorption
where does most electrolyte absorption (particulary Na) occur?
jejunum
what is the major anion that moves out of the cells and into the blood during fluid absorption in the jejunum?
HCO3
where does HCO3 and H end up during fluid absorption in the ileum?
into the lumen
enzyme that converts CO2 and H2O to H+ and HCO3
carbonic anhydrase
How does Na move into the cells in the jejunum?
1. Cotransport with amino acids
2. Cotransport with a monosaccharide
3. exchange with H ions
what do we see on the apical surface of an epithelial cell in the ileum that we don't see in the jejunum?
a Cl, HCO3 exchange mechanism
what do we see on the basal surface of an epithelial cell in the ileum that we don't see in the jejunum?
Cl transporter
what is moved into the lumen by epithelial cells of the ileum?
H and HCO3
which 2 channels are seen on the apical surface of an epithelial cell in the colon?
Na and K
how does aldosterone work?
promotes Na absorption. It does this by acting on a gene in the nucleus of epithelial cells in the colon to increase synthesis of Na channels. With more Na channels, more Na is absorbed and moves into the cell which increases activity of the Na-K-ATPase. More K is pumped in and is then secreted across the apical membrane into the intestinal lumen.
what is aldosterone?
hormone released when volume of ECF is decreased in the body which promotes Na absorption.
why is diarrhea life threatening?
rapid loss of large volumes of extracellular-type fluid. This causes a reduction in extracellular fluid volume, decreased intravascular volume and decreased arterial pressure.

The loss of specific electrolytes is also a major concern on top of circulatory collapse. The major electrolytes lost in cases of diarrhea are HCO3- and K+. The loss of too much HCO3- causes hyperchloremic metabolic acidosis because of the decreased buffering the blood, and the excessive loss of K+ causes hypokalemia.
What are The intestinal crypts are responsible for?
secreting fluid and electrolytes
What is one the surface of the apical membrane of the crypt cells?
Cl channels
What is one the surface of the basolateral membrane of the crypt cells?
Na+-K+ ATPase as well as a Na+-K+-Cl- cotransporter system
Are the Cl channels on the apical membrane of the crypt cells usually open or closed?
closed but can be opened by stimulation from hormones and NTs along the basolateral membrane
what either VIP or ACh are bound to cryptic cells?
activate adenylyl cyclase by binding to a GPCR to convert ATP to cAMP; the cAMP opens the Cl- channels.
What is the major ion that drives intestinal fluid absorption?
sodium
what is the major ion that drives intestinal fluid secretion
chlorine
what happens simultaneously as Cl is driven into the cryptic cells?
Na and water move paracellularly through leaky tight junctions and follow Cl
what controls secretion in the small intestine?
VIP and ACh
what term refers to the high chloride content in fluid being lost, metabolic acidosis, and the loss of too much HCO3?
hyperchloremic metabolic acidosis
what could result from dec surface area for absorption (ex: inflammed bowels)?
diarrhea
what can lactose intolerance result in?
osmotic diarrhea
what results from a massive increase in crypt cells?
secretory diarrhea
infection by enteropathic bacteria is a common cause for?
secretory diarrhea
what is caused by the presence of nonabsorbable solutes in the intestinal lumen (i.e. lactose intolerance)?
osmotic diarrhea
The process of osmotic diarrhea?
nonabsorbable solutes in the intestinal lumen cause water to move into the lumen in order to attempt to balance out the osmotic gradient across the apical membrane. Bacteria in the intestines can degrade lactose into even more osmotically active solutes making the problem worse.
cellular mechanism by which toxins released from some enteropathic bacteria result in secretory diarrhea?
toxins that chemically modulate the G protein (ADP ribosylation) in crypts cells. GTP cannot be broken down; therefore, the G protein remains constantly active.
AC in constantly simulated → constant high levels of cAMP → high levels of Cl channels in the apical membrane → high levels of Cl secretion → high levels of Na and water secretion
Muscle fibers connected by gap junctions that rapidly conduct action potientials through tissue?
Unitary smooth muscle
Periodic contractions followed by relaxation. These are involved in mixing and propulsion.
Phasic contractions
Constant levels of contraction. Found in sphincters.
Tonic contractions
What are slow waves?
Intrinsic activity in smooth muscle of the GI tract controlled by pacemaker cells (interstitial cells of Cajal)
What cells control the pacing of slow waves?
Cells of Cajal
What is the chewing reflex?
Involuntary reflex controlled by brainstem. Creates an ossilating movement of the jaws.
Where is the swallowing reflex controlled?
In the swallowing center of the medulla.
What are the 3 phases of swallowing?
Oral phase, pharyngeal phase and esophageal phase.
What muscle type makes up the upper esophageal sphincter?
Skeletal muscle
What do primary peristaltic waves do?
Moves the food through the esophagus.
What do secondary peristaltic waves do?
Continues to move the bolus through the esophagus if some was left behind after primary peristaltic waves.
What muscle type is the Lower esophageal sphincter made of?
Circular smooth muscle
What does VIP do to the LES?
Causes it to relax.
Which nerve releases VIP?
Vagus nerve
What is receptive relaxation?
Relaxation of the fundus and upper body of the stomach in anticipation of food.
What is chyme?
Food entering the stomach and mixing with gastric fluid.
What do mixing waves do?
Mix up chyme and break up food particles.
What does gastrin promote?
Strong mixing waves.
What inhibits mixing waves?
Secretin and GIP
What does motilin do?
Controls the migrating myoelectric complex.
What are the migrating myoelectric complexes?
These occur when there is leftover chyme in the stomach and duodenum. They occur about every 90 minutes and push along the leftover chyme.
What stimulates CCK?
Fat in the dueodenum
What does CCK do to the emptying of the stomach?
Slows it down.
What are segmentation contractions?
Contractions that mix chyme and expose it to enzymes and fluids.
What are peristaltic contractions?
Contractions that propel chyme through the GI tract.
Where is the vomiting reflex controlled?
In the vomiting center of the medulla.
When does chyme become feces?
When the contents of the ilium enter the cecum.
What does the ileocecal sphincter do? And what triggers it?
It relaxes to let feces into the colon. it is triggered by distension of the small intestines.
WHat are Haustral contactions?
segmentation contractions in proximal colon that mix and break up feces.
How often do mass movements occur?
1-3x a day, often after eating.
What is a mass movement?
When feces is moved long distances.
Explain the gastrocolic reflex?
Afferent nerves in stomach sense distension, which stimulates efferent nerves in the colon and triggers mass movements.
What is the rectosphincteric reflex?
When there is feces in the rectum, rectal distension is sensed by afferents in the rectal wall and that triggers a parasymp reflex that triggers paristalsis. This relaxes the internal anal sphincter and pushes the feces against the external sphincter.
What is the Valsalva maneuver?
Forced expiration with a closed glottis that stimulates the rectosphincteric reflex. Creates increased pressure in the abd.
Is the external anal sphincter under voluntary or involuntary control?
Voluntary.
Is the internal anal sphincter under voluntary or involuntary control?
Involuntary
What kind of smooth muscle is found in the alimentary canal?
Unitary smooth muscle.
Where is skeletal muscle found?
In pharynx, upper 1/3 of esophogus and external anal sphincter.
What is the frequency of slow waves in the stomach? Dueodenum?
Stomach: 3 ossilations per minute.
Duodenum: 12 ossilations per minute.
What is the purpose of chewing food?
Mixing food particles w/ saliva, it is the beginning of digestion and it reduces the size of food particles.