GI - Physiology: Exocrine Functions of Pancreas

acute pancreatitis:

a sudden attack causing inflammation of the pancreas. The most common cause of acute pancreatitis is gallstones

what provides the bulk of enzymes for protein, carbs and fat digestion?

the pancreas

The most common cause of acute pancreatitis:

gallstones

Hereditary Pancreatitis is related to...

inherited abnormalities

in acinar cells, there are vesicles containing enzymes in the cytoplasm and upon stimulation what happens?

they fuse to the apical membrane of an acinar cell and are spit out into the acinar space

what cancer is the fourth most common cause of cancer death in men and the fifth in women?

pancreatic cancer

ductal cells produce what?

bicarbonate and fluid

Pancreatic juice is composed of two secretory products critical to proper digestion:

digestive enzymes and bicarbonate

where are the digestive enzymes of the pancreas synthesized and secreted?

from the exocrine acinar cells

where is bicarbonate secreted from?

the epithelial cells lining small pancreatic ducts, ductal cells

what are positive regulators of enzyme release in the acinar cells?

- vagal acetylcholine

- cholecystokinin

what is the positive regulator of increased fluid/HCO3- in the ductal cells?

secretin

the major amount of fluid is produced by what cells in the pancreas?

ductal cells

does CCK or ACh stimulate ductal cells?

NO, ductal cells are only stimulated by secretin

does secretin stimulate acinar cells?

NO, anicar cells are only stimulated by CCK and ACh

What are 2 sources of the bicarb that is secreted into the acinar space?

- plasma

- creation in ductal cells by way of carbonic anhydrase

on the basolateral surface of an ductal cell, how is bicarb transported from the plasma into the cell?

through a sodium and bicarbonate cotransporter

on the apical surface of an ductal cell, how is bicarb excreted from the cell?

through the exchange of chloride (antiporter)

secretin release is stimulated by what?

acidic chyme

upon stimulation by acidic chyme, what does secretin do?

acts on ductal cells to increase sodium bicarbonate release

CCK release is stimulated by what?

proteins and fats in chyme

upon stimulation by proteins and fats in chyme, what does CCK do?

causes acinar cells to release increasing amount of digestive enzymes

what phase provides majority of the stimulation or enzyme secretion for the exocrine pancreas?

intestinal phase

what are the most important regulators of fluid secretion?

secretin acting on ductal cells

what are the most important regulators of enzyme secretion?

CCK AND ACh acting on acinar cells

where is CCK found?

I cells in the duodenum

what enzymes are active upon secretion from acinar cells?

lipolytic enzymes

- lipase

nucleases

amylolytic enzymes

- alpha amylase

- trypsin inhibitor

what enzymes are inactive upon secretion from acinar cells?

proteolytic enzymes

- trypsinogen

- chymotrypsin

- proelastase

- procarboxypeptidase A and B

why is trypsin inhibited?

- trypsin activates all other proteolytic enzymes

to prevent proteolytic enzymes from damaging ductal cells

what guards against accidental protease activity in ducts?

trypsin inhibitor

there is a membrane bound enteropeptidase expressed on the cell surface of enterocytes that does what?

upon coming into contact with trypsinogen, it cleaves it into trypsin which cleaves all other proteases to their active form including itself

can enteropeptidase cleave any inactive proteases to their active form other than trypsinogen?

NO

is the amount of trypsin inhibitor secreted comparable to the amount of trypsin that is activated in the small intestine?

NO, The amount of trypsin inhibitor secreted by the pancreas is small in comparison to the amount of trypsin that is activated in the small intestine.

are proteins cleaved by peptidases cleaved into AA?

NO, they are cleaved into peptides

what is a major component of dietary fats?

triglycerides

can triglycerides be directly absorbed across intestinal mucose?

NO, it must first be digested into a 2-monoglyceride and 2 free fatty acids

what is the digestible form of fats?

2-monoglyceride and 2 free fatty acids

- broken down from a triglyceride

T or F: all vertebrates contain cells that have been identified to produce an enzyme that hydrolyzes cellulose

FALSE no vertebrate cell has been identified

- herbivores have bacteria in their gut that produce enzymes to break it down for their host

does secretin affect enzyme secretion?

NO, only act on ductal cells

Secretin is secreted from what cells?

S cells

amino acids and peptides work through which mechanisms to elicit a pancreatic response (enzyme and bicarbonate secretion)?

vago-vagal reflex

CCK release

what stimuli work through al three mechanisms (vago-vagal reflex, CCK release and secretin release) to elicit a pancreatic response (enzyme and bicarbonate secretion)

fatty acids and duodenal acid load

the vasovagal reflex has what effect of pancreatic secretions?

increases enzyme release from acinar cells

the vasovagal reflex is stimulated by:

- peptides/amino acids

- fats

- H+

CCK has what effect of pancreatic secretions?

increases enzyme release from acinar cells

CCK is stimulated by:

- peptides/amino acids

- fats

- H+

secretin has what effect of pancreatic secretions?

increases fluid and HCO3- by ductal cells

secretin is stimulated by:

fats and H+