GI Tract Part 2 Flashcards
length of small intestine in humans
~4-6 m
the small intestine in the primary site of (2)
absorption
digestion
duodenum, length
jejunum length
ileum length
~25 cm (~1 ft)
~2 m
~3 m
Mucosa & submucosa throughout small intestine arranged in valve-like folds/ rings,
plica circulares
plica circulares
= valves of Kerkring
increase surface
plica circulares contain — core
submucosal core
Mucosal surface made up of —, ~1 mm long, contain core of — —
villi
lamina propria
Between villi are
crypts of Lieberkuhn
Coeliac disease (gluten enteropathy) causes (2)
villus blunting & atrophy
Coeliac disease(gluten enteropathy) causes villus blunting & atrophy results in (2)
malabsorption & weight loss
Epithelium supported by connective tissue lamina propria, containing capillaries & lymphatics for
absorption of nutrients
Intestinal villi lined by
simple columnar epithelium
Mucosal cells of the small intestine called —, cover surface of villi
enterocytes
— surface highly folded, modified into microvilli
Apical/luminal
Apical/ luminal surface highly folded, modified into microvill is also known as
striated or brush border
microvilli increase surface area for
absorption
microvilli are coated with protective
glycocalyx of disaccharides
glycocalyx of disaccharides is a site of
membrane digestion
Interspersed among enterocytes
are
mucus secreting goblet cells
Interspersed among enterocytes
are mucus secreting goblet cells;
Synthesize
mucinogen, resulting in mucus
mucinogen is stored in
membrane-bound
granules
mucinogen (2) epithelium
lubricates and protects
Actively dividing — — located
at base of crypts
stem cells
Cells migrate up villus, mature, &
are —
shed
Entire epithelial lining replaced in
3-
5 days
— cells found at base of crypts
Paneth
Paneth cells found at base of crypts; contain large eosinophilic granules—produce antibacterial proteins called —, and enzymes, including —
defensins
lysozyme
Small #’s of — cells scattered throughout
enteroendocrine (APUD)
enteroendocrine cells regulate (2)
GI mobility and secretion
“S” cells secrete
secretin (stimulate release of bicarbonate from pancreas)
“I” cells secrete
cholecystekinin, or CCK (stimulates pancreatic secretion & contraction of gallbladder)
“A” cells secrete
glucagon
increase blood sugar
“K” cells secrete
GIP (gastric inhibitory peptide)
MALT located in (2)
lamina propria &
submucosa of small intestine
MALT contains plasma cells, which sec…
IgA
Epithelium contains enlarged
“M” cells (microfold)
Epithelium contains enlarged “M” cells (microfold) —squamoid
enterocytes modified for (2)
Ag sampling, uptake of
macromolecules
May also see — —,
dome-shaped areas grossly visible
on surface of mucosa, project into
lumen
Peyer’s patches
duodenum is characterized by presence of
— — in submucosa
Brunner’s glands
Brunner’s glands contain large numbers of
highly convoluted,
branched, tubuloalveolar
submucosal glands
Brunner’s glands secrete (2), unique to duodenum
mucus and zymogens
Main function of duodenum (2),
assisted by pancreas & gallbladder
neutralize gastric acid & pepsin
Pancreatic duct & bile duct empty into duodenum at
major duodenal papilla
Chyme from stomach stimulates release of (2) hormones from APUD cells
secretin& CCK
secretin& CCK both promote section of
exocrine pancreas
Pancreatic secretions highly alkaline, due to
bicarbonate (neutralize stomach acid)
CCK also stimulates contraction of gallbladder & release of
bile acids
bile acids act as
emulsifying agents for digestion of lipids, form micelles
Pancreatic secretions also contain proteolytic enzymes (2) for digestion of proteins
(+ amylase & lipase)
trypsin & chymotrypsin
Secreted as inactive precursors (zymogens),
trypsinogen & chymotrypsinogen
Secreted as inactive precursors (zymogens), trypsinogen & chymotrypsinogen to prevent —
autolysis
trypsin activated by —
enterokinase
trypsin then activates —
chymotrypsin
two steps of digestion
luminal digestion
membrane digestion
luminal digestion involves
mixing of chyme with
pancreatic enzymes
luminal digestion results in
molecular breakdown
membrane digestion involves
enzymes of glycocalyx on plasma membrane of enterocytes
Enterocytes synthesize various enzymes,
3) & produce various carrier proteins for absorption of (2
peptidases, peptide hydrolases, disaccharidases
carbohydrates & AA’s
