Small Intestine and Pancreas Flashcards
the intestinal structure amplifies what?
surface area
transport of water and solutes across living membrane depends on what process?
diffusion
the longitudinal folds on the surface of the small intestine are known as what?
folds of Kerckring (plicae circulares)
what projects from the folds of kerckring
villi
what lines the entire mucosal surface of small intestine
villi
what protrudes from the surface of intestinal cells?
microvilli
the appearance of the microvillus gives them the term?
brush border
what projects down into the surface at base of each villus
crypt
how many crypts are there per villus
3
name the cell types found in the small intestine
enterocytes
goblet cells
crypt cells
enterocytes of small intestine (what type of cell are they, where are they found, and what feature do they have)
columnar epithelial cells
in villus
microvilli protrude from apical surface
enterocytes of small intestine (name the functions it performs)
digestion, absorption, secretion
what location in the villus are enterocytes of the small intestine best at digestion and absorption
those found at the tip of the villus than at the base
goblet cells of small intestine (where are they, what do they do)
interspersed with enterocytes in villus
secrete mucus
crypt cells (where are they found, what do they do)
found in crypts at base of villus
secrete fluids and electrolytes
what cells are proliferative cells in the intestine and what do they form
crypt cells
can form both enterocytes and goblet cells
what are the functions of the small intestine
mix chyme with digestive juices and bile to facilitate digestion and absorption
further reduce size of chyme particles, which increases solubility
bring chyme into contact with absorptive surface of microvilli
propel chyme from duodenum to colon
what types of contractions occur in the small intestine
segmentation
peristaltic
migrating myoelectric complex
what is the most common type of intestinal contraction
segmentation
segmentation contraction (what is contracting and what does that contraction do)
circular smooth muscle of isolated wall contracts
forces chyme toward both stomach and colon
segmentation contraction (upon relaxation of the circular smooth muscle what happens to chyme and what is the effect of this)
returns to original segment
effect is mixing of chyme with digestive juices
is there net movement of chyme in segmentation contraction (if so which direction and why)
net movement of chyme toward colon
due to higher frequency of contraction in proximal than distal intestine
peristaltic contractions (function, and where do they occur)
serve to propel chyme down small intestine
occur only over short distances
migrating myoelectric complex (what does it do, when does it occur)
clears remaining chyme in small intestine
occurs about every 90 minutes
intestinal slow waves require what for contractions to occur
action potentials
what happens to slow wave frequency going from proximal to distal intestine
slow wave frequency decreases distally
peristaltic reflex/rush (what is it, what initiates it)
contraction that moves intestinal contents along small intestine
initiated by chyme in intestine which either distends wall or greatly irritates mucosa (also severe cases of infectious diarrhea)
intestinointestinal reflex (what is it and what does it prevent)
overdistention of one segment of intestine inhibits contractile activity in rest of intestine
prevents moment of material into already beverly distended section of bowel
gastroileal reflex (what triggers it, what does it do)
gastric secretion and emptying triggers increased peristalsis in ileum
causes relaxation of ileocecal sphincter and moment of ill contents into large intestine
what reflex moves intestinal contents along small intestine
peristaltic reflex/rush
what reflex cases relaxation of ileocecal sphincter and movement of ill contents into large intestine?
gastroileal refelx
what reflex causes the urge to defecate shortly after starting a meal
gastrocolic reflex
gastrocolic reflex (what does it do, what triggers it, what is eventual outcome)
urge to defecate shortly after starting meal
presence of food in stomach triggers increased colonic motility
eventually leads to evacuation of colon to make way for remains of next meal
what types of cells are found in the pancreas
acinar cells
centroacinar cells
duct cells
what do acinar cells of the pancreas do?
produce:
peptidases- digest proteins
lipases- digest fat
amylases- digest carbohydrates
what do centroacinar cells of the pancreas do?
secrete pancreatic juice containing high concentration of HCO3- (neutralizes gastric acid in duodenum and brings contents within pH range for enzymatic digestion)
pancreatic juice secreted from centroacinar and duct cells has a high concentration of what and why?
HCO3- (neutralizes gastric acid in duodenum and brings contents within pH range for enzymatic digestion)
what do duct cells of pancreas do?
secrete pancreatic juice containing high concentration of HCO3- (neutralizes gastric acid in duodenum and brings contents within pH range for enzymatic digestion)
pancreatic juice tonicity is what compared to plasma (and at what rates of secretion)
isotonic
at all rates of secretion
at low flow rates what is the primary composition of pancreatic juice?
Na+
Cl-
at high flow rates what is the primary composition of pancreatic juice?
Na+
HCO3-
compared to plasma what is the [HCO3-], [Cl-], and [K+] of pancreatic juice
[HCO3-]- higher in pancreatic juice than plasma
[Cl-]- lower in pancreatic juice than plasma
[K+]- about the same as in plasma
as flow rate increases what happens to [HCO3-], [Cl-], [Na+] and [K+] of pancreatic juice
[HCO3-]- increases
[Cl-]- decrease
[Na+]- stays the same
[K+]- stays the same
what produces initial pancreatic juice and what is its primary composition
acinus produces small volume initial pancreatic juice
primarily Na+ and Cl-
what modify the initial pancreatic juice produces by acinus (and how)
ductule and centroacinar cells
secreting HCO3- and absorbing Cl-
in ductule and centroacinar cells how is HCO3- formed
HCO3- and H+ are formed from H2O and CO2 via carbonic anhydrase
venous blood from actively secreted pancreas is what compared to a nonnsecreting pancreas
lower pH in actively secreting pancreatic venous blood (H+ in blood from carbonic anhydrase reaction)
H+ is transported out of ductule and centroacinar cells to where, in exchange for what, and by what?
H+ goes into blood
in exchange for Na+
via Na+/H+ antiporter
what happens to H+ once in the blood
reforms CO2 with HCO3- (the CO2 can then freely reenter the cell and become HCO3-)
HCO3- in ductule and centroacinar cells is exchanged to where, for what?
HCO3- transported across apical membrane to lumen
exchange for Cl-
how does Cl- enter lumen
through channel in apical membrane
what is messed up (in regards to pancreas) in cystic fibroses
the apical Cl- channel is mutated
the rate of HCO3- secretion in ductule and centroacinar cells is dependent on what
Cl- being present in lumen
what happens to the Na+ inside ductule and centroacinar cells
actively pumped out of cell via Na/K ATPase (keeps intracellular Na+ low for the Na/H antiporter)
what follows HCO3- into lumen and why?
Na+
to preserve electrical neutrality
how does water move into lumen of pancreas?
somatic gradient (b/c pancreatic ducts are permeable to water)
in terms of water movement what is difference between pancreatic duct and salivary duct
pancreatic duct is permeable to water
salivary duct is not preamble to water
what protects pancreas from autodigestion
trypsin inhibitor secretion
pancreatic lipase and amylase are secreted in what form
active
pancreatic proteases (trypsin and chymotrypsins) are secreted as what?
inactivated forms
pancreatic proteases (trypsin and chymotrypsins) are activated where?
small intestine
during cephalic and gastric phases of digestion what regulates pancreatic secretion (what cell are acted on and by what, what triggers control and by what reflex, what is it mostly controlled by)
ACh acting on acinar and ductule cells
distention of stomach initiates vagovagal reflex (stimulates secretion)
mostly digestive enzymes
during intestinal phase of digestion what stimulates regulates pancreatic secretion
stimulated by acid and by fat and protein digestion products in duodenum
during what phase of digestion is the majority of pancreatic control
intestinal
during intestinal phase of digestion what does acid do to pancreatic section
acid releases secretin from S cells in duodenum
secretin acts on ductule cells to increase HCO3- secretion (neutralizes acid)
during intestinal phase of digestion what do protein and fat digestion products do to pancreatic section
release cholecystokinin (CCK) from I cells in duodenum CCK acts on acinar cells to increase enzyme secretion
secretin acts on what type of pancreatic cells and does what?
secretin acts on ductule cells to increase HCO3- secretion (neutralizes acid)
CCK acts on what type of pancreatic cells and does what?
CCK acts on acinar cells to increase enzyme secretion
act on duct cells to potentiate action of secretin
during intestinal phase of digestion what do protein and fat digestion products as well as acid initiate what reflex and what does that do
vagovagal reflex
stimulates acid secretion
what potentiates the action of secretin on ductal cell secretion
CCK and ACh
Cystic Fibrosis (whats wrong, and what does that lead to)
mutation occurs in Cl- channel in apical membrane of cell
reduces secretion of both aqueous and enzymatic component of pancreatic juice (lack of aqueous secretion leads to concentration of pancreatic juice, which block secretion of enzymatic compartment)
malabsorption and steatorrhea are common in patients with?
cystic fibrosis
what is most commonly caused by chronic alcoholism or gallstone (can be caused by high triglycerides and smoking)
pancreatitis
what are the symptoms of acute pancreatitis
severe abdominal pain swollen and tender abdomen nausea and vomiting diarrhea fever
greatly elevated serum lipase and amylase levels are indicative of what?
pancreatitis
what is the issue in pancreatitis
activated enzymes digest pancreatic tissues
in US what is mot common cause of chronic pancreatitis
repeated episodes of acute pancreatitis induced by alcohol abuse
high protein concentration in pancreatic juice is indicative of what?
chronic pancreatitis
How does Na+ from pancreatic juice enter lumen of small intestine
between pancreatic ductal cells
an example of negative feedback in the pancreas would be?
Acid stimulates secretin which then stimulates bicarbonate which reduces the acidity