Accessory Digestive Organs Flashcards
liver and pancreas are embryological outgrowths of
primitive gut
liver and pancreas function as
accessory digestive orango
— is largest gland & internal organ
Liver
liver is divided into
4 lobes (L, R, caudate, & quadrate)
Major functions of liver: (6)
- Detoxification of metabolic waste (e.g., deamination of AA’s urea)
- Metabolism & detoxification of drugs & toxins (e.g., alcohol, abx)
- Destruction of senescent rbc’s
- Recycling of Hb via synthesis & secretion of bile
- Synthesis of plasma proteins (clotting factors, albumin, lipoproteins)
- Miscellaneous metabolic functions (e.g., glycogen synthesis & storage, gluconeogenesis)
External surface of liver covered by connective tissue capsule,
Glisson’s capsule
Monosaccharides & AA’s from digestion enter liver via
hepatic portal V
the hepatic portal vein carries –% of blood to liver
~75-80
hepatic portal vein also carries potentially toxic compounds absorbed from diet to liver to be
conjugated or detoxified
Oxygenatedblood supplied to liver by
hepatic A, a branch of celiac trunk
hepatic A, a branch of celiac trunk goes to — — in hepatic lobules
portal artery
portal artery carries only
~20-25% of blood to liver
portal artery mixes with
unoxygenated blood from portal V to perfuse liver cells
Liver is a — rich, but — poor environment
nutrient
O2
Venous drainage of lobules via
central Vv
central Vv leads to
hepatic V
Liver cells are called
hepatocytes
Most hepatocytes —, but
some are
diploid
polyploid &/or binucleate
hepatocytes contain large #’s of
cytoplasmic
granules (rER & lysosomal
products) & storage products
Aging hepatocytes accumulate
brown pigment,
lipofuscin
Individual hepatocytes
polygonal, arranged in
anastomosing cords
paralleled by venous
sinusoids
Sinusoids lined by
sinusoidal
lining cells, a discontinuous
endothelium, with gaps
between endothelial cells
Between sinusoidal lining
cells & hepatocytes is
space of Disse
space of Disse
also known as
continuous with
perisinusoidal space
lymphatics
Hepatic cords & sinusoids
supported by
reticulinfibers
Type III collagen
Within sinusoids & space of
Disse are
phagocytic Kupffer
cells (macrophages)
Occasional — cells between
hepatocytes
Ito
Ito cells
fat-storing cells
containing lipid droplets,
used for Vit A & D storage
Cords of hepatocytes
arranged in —
lobules
Classic lobule—
based on — —
roughly —, with — — in middle of lobule
blood flow
hexagonal
central V
SKIPPED
central V in middle of lobule
centrilobular V,
terminal hepatic venule
Outer margin of each lobule
delimited by thin,
connective
tissue septum
Portal tracts/ triads
located at each “corner”,
contain
portal A, V, L, &
bile duct
Blood enters from portal
tracts, percolates
through sinusoids of
lobule, drains via
central V
Portal lobule—
triangular
area; based on bile flow
(opposite to blood flow)
— — in center & — — at corners
Portal triad
central Vv
Acinus—
diamond–shaped region between neighboring central Vv
Central Vv located
along longitudinal axis, with portal tracts at sides
Combines aspects of (4)
blood flow, oxygenation, metabolism & pathology
Acinus divided into
zones 1, 2, & 3
Hepatocytes in different zones have different
metabolic environments
Zone 1—
(perilobular zone= periportal)—closest to portal tract, receives mostoxygenated blood
zone 1 is most susceptible to
toxic injury
Zone 2—
(intermediate zone)
Zone 3—
(centrolobular zone)—furthest from portal tract, closest to central V
zone 3 receives…
least oxygenated blood
zone 3 is most susceptible to
ischemic injury
Liver functions in detoxification or metabolism of various
drugs, toxins, metabolites (e.g., ethanol, pesticides, & carcinogens) via microsomal mixed function oxidase system of sER, or peroxidases of peroxisomes (P450 system)
A common sequela to repeated
insults or chronic disease is
cirrhosis
Cirrhosis is characterized by (2), followed
by (2)
hepatic degeneration & necrosis
fibrosis & nodular regeneration
Portal hypertension—associated
with
cirrhosis (due to fibrosis,
blockage of blood flow)
Liver has ability to
regenerate
Liver functions divided into (2)
exocrine & endocrine
secretion of products via ducts
exocrine
secretion of products without ducts; directly into bloodstream
endocrine
Endocrinefunctions of liver— (5)
• Synthesis of plasma proteins (e.g., fibrinogen, urea, albumin,
prothrombin)
• Synthesis of glucose
• Gluconeogenesis (from non-carbohydrate sources, e.g., AA’s & lipids)
• Storage & release of glycogen, lipids & lipoproteins
• Vit A & D storag
Exocrine (secretory) function of liver
bile synthesis
Bile is — agent, facilitates
emulsifying
hydrolysis of lipids by pancreatic lipases
Adult human liver secretes – liter bile/ day
~1
Bile flow from liver increases by hormones such as (3)
secretin, CCK, & gastrin from enteroendocrine (APUD) cells
Bilesynthesized by — & secreted into network of — —
hepatocytes
bile canaliculi
Small canals between —, formed by
hepatocytes
grooves in plasma membranes of adjacent cells
Direction of bile flow — to blood flow, from —, in series of —- —- —
opposite
canaliculi
progressively larger ducts
bile synthesis includes (2)
bile ducts (portal
triads) & larger intrahepatic
ducts (scattered throughout
parenchyma)
Bile eventually enters
duodenum at —, following (2)
major duodenal papilla
period of storage & modification in gallbladder
Gallbladder
Muscular sac located in depression along surface of liver
Gallbladder is used to store & concentrate —; volume – ml
bile
~100
Gallbladder is lined by
simple columnar epithelium with apical microvilli
simple columnar epithelium with apical microvilli of gallbladder is used for
resorption of water
Gallbladder lacks a
muscularis mucosae
Lamina propria highly folded with occasional
tubuloalveolar mucus glands
CCK (cholecystokinin) stimulates
contraction of gallbladder
Components of bile (6)
Water ions electrolytes cholesterol + phospholipids (= lecithin) bile acids (= bile salts) bile pigments
— is best known bile pigment
Bilirubin
Bilirubin
non-sol breakdown product of Hb
Bilirubin glucuronide—
water-soluble form of bilirubin, conjugated with glucuronide
Pathology: Failure to absorb bilirubin or failure to conjugate it & secrete glucuronide results in (2)
accumulation of bile pigments & jaundice
Supersaturation of bile results in
gallstones (biliary calculi, cholelithiasis)
1’ cholesterol & calcium salts
Obstruction of bile ducts (choledocolithiasis) results in (2)
bile stasis, or jaundice (icterus) if severe
Chronic inflammation
cholecystitis
Sx removal of gallbladder is
cholecystectomy
Following Sx, unable to — —; need to limit — — —
concentrate bile
ingestion of fats
Pancreas (2)
Highly lobulated gland with thin, connective tissue capsule
pancreas is located in the
bend of duodenum
pancreas has both (2) components
endocrine
exocrine
Ductless endocrine pancreatic tissue located in
islets of Langerhans
Most of pancreas is
exocrine(i.e.,
with ducts)—a compound, acinar,
serous gland
Densely packed serous acini
contain
pyramidal secretory cells
surrounding a central lumen (duct)
Acinar cells contain
zymogen granules (inactive enzyme precursors)
inactive zymogen examples (4)
trypsinogen(= protrypsin),
chymotrypsinogen(=prochymotrypsin),
amylase,
lipase
Trypsin & chymotrypsin are —; amylase breaks down — & lipases digest —
proteases
carbohydrates
lipids
Empty into — —(add bicarbonate & water to pancreatic sections; neutralize acidic chyme from stomach => optimal pH for pancreatic enzymes)
intercalated ducts
Duct cells that form beginning of intercalated duct sometimes visible in center of acini, called
centro-acinar cells
Intercalated ducts empty into
— —-, which exit into
larger intralobularducts larger interlobular (=extralobular) ducts
Pancreatic secretions enter duodenum via
pancreatic ductat major duodenal papilla
Principle regulators of exocrine pancreas—
polypeptide hormones secreted by enteroendocrine (APUD) cells
1 secreted by stomach:
gastrin
gastrin: secreted by “—” cells of pyloric stomach; stimulates secretion of — —
G
pancreatic fluid
3 secreted by duodenum:
secretin
CCK
enterokinase
secretin—secreted by “—” cells; stimulates secretion of
S
bicarbonate by cells of intercalated ducts
CCK (cholecystokinin=pancreozymin); secreted by “—” cells, stimulates acinar cells to secrete —
I
zymogens
enterokinase—
converts trypsinogen which forms trypsin (within small intestine), which converts chymotrypsinogen which forms chymotrypsin (digests proteins)
Cascade rxn prevents pancreas from
digesting itself
Pancreatitis
autodigestion
of pancreas brought on by
alcoholism
Cascade rxn of Pancreatitis breaks down which results in
Premature conversion of chymotrypsinogen to
chymotrypsin & autolysis
Pancreatitis is —,
severe
acute Pancreatitis can be fatal within hours