CNS Primer Flashcards
Structures of the alimentary tract
mouth, tongue, teeth, and throat
the chief cells of the stomach secrete
lipase & pepsinogen
lipase breaks
down dietary triglycerides into
into free fatty acids and diglycerides
(diacylglycerols),
pepsinogen is the precursor of,
pepsin
pepsin initiates the hydrolysis of
proteins
parietal cells of the stomach secrete
Intrinsic factor (IF) & HCl
Intrinsic factor is a protein required for absorption of
vitamin B12,
Mucous cells of the stomach secrete mucus
containing
glycoproteins and bicarbonate
Gastric acid performs a number of preliminary digestive roles that require an
acidic environment, including
- destruction of microorganisms,
- activation of pepsinogen to
pepsin, - activation of intrinsic factor,
- denaturation (loss of three-dimensional conformation) of
macromolecules, - facilitation of the breakdown of protein and polypeptides by pepsin.
The presence of food protein in the stomach triggers gastric endocrine cells to secrete
gastrin
Gastrin acts on gastric parietal and chief cells to stimulate intragastric secretion of
HCL & pepsinogen
gastrin secretion is inhibited by increased/decreased intragastric acidity.
Increased
Peristaltic contractions of the distal stomach propel digesta toward the __________.
Simultaneously, the _______________ contracts in opposition to gastric peristalsis, but does
not close.
gastric pylorus
common name for the luminal surface of the small intestine
brush border
brush border is composed of
microvilli
microvilli increase/decrease the absorptive surface area of the small intestine
increase
Absorptive _______ originate from stem cells in the intervillar crypts. Following their migration to the luminal surface of the mucosa, __________ fully differentiate, survive about 72 hours, undergo apoptosis (preprogrammed cell death) and lose their attachment to the mucosal basement
membrane (“desquamation”).
enterocytes
most proximal upper section of the small intestine where chemical
degradation of partially digested food into individual nutrients begins.
short duodenum,
second section of
the small intestine,
second section of
the small intestine,
distal small intestine,
ileum,
Acidic chyme entering the proximal duodenum stimulates the enteric secretion of
secretin
Secretin stimulates pancreatic secretion of ________ into
the ductal system that terminates in the common bile duct.
bicarbonate
fat or protein
entering the proximal duodenum stimulate duodenal secretion of
cholecystokinin
Cholecystokinin stimulates pancreatic secretion of ________ into the ductal systemand stimulates gall bladder
contraction, propelling bile into the common bile duct.
zymogens
(inactive digestive enzyme precursors)
zymogens
Increasing duodenal distension triggers secretion of
gastric inhibitory
peptide
This peptide inhibits gastric motility and slows the rate of further gastric emptying when increasing duodenal distension
gastric inhibitory
peptide
Pancreatic zymogens that play major roles in food digestion include
- trypsinogen
- proelastase
- chymotrypsinogen
- procolipase
- procarboxypeptidase A
- procarboxypeptidase B.
When pancreatic zymogens reach the small intestine,
duodenal enterocytes secrete ______, which converts trypsinogen to trypsin.
enterokinase
enterokinase enzyme is required for activation of
trypsin
trypsin zymogens to
- elastase
- chymotrypsin
- colipase
- carboxypeptidase A
- carboxypeptidase B
Trypsin,
chymotrypsin and elastase are ______ proteases and ____peptidases (hydrolyze peptide bonds within polypeptides).
serine proteases
endopeptidases
the proteases require a serine is at the enzymes’ active sites
serine proteases
This type of enzyme hydrolyzes peptide bonds within polypeptides
endopeptidases
Carboxypeptidases are _____-requiring metalloenzyme exopeptidases that cleave single carboxyterminal amino acids from polypeptides.
zinc
Secreted by the pancreas, ________ performs initial digestion of starches to produce glucosyl oligosaccharides and
disaccharides
amylase
Secreted by the pancreas, ______ hydrolyzes dietary fats that have been emulsified by bile salts into fatty acids and glycerol
lipase
Secreted by the pancreas, ____________ cleaves cholesteryl esters;
ribonuclease and deoxyribonuclease.
cholesteryl esterase
The brush
border enzymes that complete the final steps in the hydrolysis of amylase-digested carbohydrates to
monosaccharides and of protease-digested proteins to absorbable free amino acids, dipeptides
and tripeptides.
Ectozymes
The categories of ectozymes produced by enterocytes and attached to microvillar surfaces of the small intestine
- oligosaccharidases
- disaccharidases
- pepidases
Pancreatic bicarbonate buffers ____ into a weaker acid
gastric HCl
The efficiency of digestive
enzymes is affected primarily by ____ pH.
local
The pH optimum for salivary amylase is a pH
6.75-7.00
The pH optimum for gastric pepsin and lipase is a pH
1.5-3.5
Enzymes that are deactivated by the presence
of free protons include
gastric lipase, salivary amylase and lingual lipase.
gastric lipase, salivary amylase and lingual lipase function most efficiently at _____ or higher _____ pH.
neutral, alkaline