11/16: Accessory Digestive Organs Flashcards
What are the major functions of the liver?
- Detoxification of metabolic waste (e.g., deamination of AA’s –> urea)
- Metabolism & detoxification of drugs & toxins (e.g., alcohol,
antibiotics) - Destruction of senescent RBC’s
- Recycling of Hb via synthesis & secretion of bile
- Synthesis of plasma proteins (clotting factors, albumin,
lipoproteins) - Miscellaneous metabolic functions (fat, carbohydrate,
proteins, etc.)
How do the products of digestion enter the liver via?
Hepatic portal vein
What percent of blood is carried to the liver via the hepatic portal v?
75-80%
What else does the hepatic circulation carry?
potentially toxic compounds absorbed from diet to liver to be conjugated or detoxified
How is oxygenated blood supplied to the liver via?
Hepatic artery, a branch of celiac trunk
What does the hapatic artery split into?
R/L hepatic Aa in hepatic lobules
What percent of blood does the hepatic artery carry?
20-25% of blood to liver
What does the hepatic artery blood mix with?
UNoxygenated blood from portal V to perfuse liver cells
Describe the liver in regardes to nutrients and O2
Nutrient rich, but O2 poor environment
What is the venous drainage via?
Lobules via central vv -> hepatic v -> IVC
What are the cells found in the liver?
Hepatocytes
Endothelial cells
Kupffer cells
Stellate cells (Ito cells)
What is the main functional cell?
Hepatocytes
How are hepatocytes arranged?
In plates or cords around sinusoids
Where are endothelial cells found?
Line the sinusoids
What are liver-specific macrophages?
Kupffer cells
What cells store vitamin A?
Stellate cells (Ito cells)
What is the structure of hepatocytes?
Diploid, but some polyploid or binucleate
What do hepatocytes contain?
Large #s of cytoplasmic granules (rER and lysosomal products) and storage products
What do aging hepatocytes accumulate?
Brown pigment, lipofuscin
Describe the structure and arrangement of individual hepatocytes
polygonal, arranged in anastomosing cords
What are hepatocytes paralleled by?
Venous sinusoids
What are sinusoids lined by?
Sinusoidal lining cells, a discontinuous endothelium, with gaps between endothelial cells
What are hepatic cords and sinusoids supported by?
Meshwork of reticulin fibers (Type III collagen)
What is found within sinusoids and space of disse?
Phagocytic Kupffer cells
What is occasionally between hepatocytes?
Stellate or Ito cells
What are stellate or Ito cells?
fat- storing cells containing lipid droplets, used for Vit A & D, storage
Describe the cytoplasm of a kupffer cell
Packed with black carbon particles
How can Kupffer cells be recognized?
by their oval nuclei closely associated with sinusoidal spaces
Describe the appearance of endothelial cells
Similar to kupffer, but with thinner (flatter) and denser
nuclei and with less conspicuous cytoplasm
What do hepatocytes that comprise the hepatic cords have?
Round nuclei surrounded by abundant cytoplasm
What is the function of Kuppfer cells?
remove foreign particles, they also work with the spleen to destroy old RBCs
What happens to a stellate cell in liver injury?
Becomes a transitional cell or
myofibroblast-like cellW
What is the function of a stellate cell in liver injury?
capable of synthesising collagen types I, III and IV as well as lamini
What is a thin, discontinuous, highly fenestrated endothelium that does not rest on a basement membrane?
Hepatic sinusoids
What are hepatic sinusoids separated from the hepatocytes by?
The space of Disse or the perisinusoidal space
Where are hepatic sinusoids found?
In the liver between a hepatocyte and a sinusoid
What do hepatic sinusoids contain?
Blood plasma
Where do microvilli of hepatocytes exten?
Into the hepatic sinusoids
What does the extension of microvilli allow for?
Proteins and other plasma components from the sinusoids to be absorbed by the hepatocytes
What kind of vascular channels are found within hepatic sinusoids?
Low resistance that allow blood to come into contact with hepatocytes over a large surface area
What is the flow of bile made by?
Hepatocyte & secreted into bile canaliculi between cells
What are the 3 concepts of liver lobules?
Classic hepatic lobule
portal lobule
Hepatic acinus of rappaport
What is the organization of hepatic lobules?
Cords of hepatocytes arranged in lobules
What is a classic lobule?
Based on blood flow; roughly hexagonal, with central vein in middle of lobule
What is the outer margin of each lobule delimited by?
Thin, connective tissue septum
What is located at each “corner” of a classic lobule?
Portal tracts/triads
What do portal tracts/triads contain?
Hepatic A, br. portal V, L, and bile duct
How does blood enter from portal tracts, percolates through?
Sinusoids of lobule
What drains portal tracts?
Central vein
What is a triangular area; based on bile flow (opposite to blood flow)?
Portal lobule
What makes up a portal lobule?
Portal triad in center and central vv at corners
What is an acinus?
Diamond shaped region between neighboring central vv
Where are central vv located in hepatic acini?
Along longitudinal axis with portal tracts at sides
What aspects make up the hepatic ascini?
Blood flow, oxygenation, metabolism and pathology
What is an acinus divided into?
3 zones - 1,2,3
What do hepaticytes in different zones have?
Different metabolic environments
Describe the 3 zones of the hepatic acini
Zone 1—(perilobular zone = periportal)— closest to portal tract
Zone 2—(intermediate zone)
Zone 3—(centrolobular zone)—furthest from portal tract, closest to central V
What receives most oxygenated blood;
also most susceptible to toxic injury?
Zone 1
What receives least oxygenated blood; most
susceptible to ischemic injury?
Zone 3
How does the liver function in detoxification or metabolism of drugs, toxins, metabolites?
Via microsomal mixed function
oxidase system of sER, or peroxidases of peroxisomes (P450 system)
What is cirrhosis characterized by?
hepatic degeneration & necrosis, followed by fibrosis & nodular regeneration
What is associated
with cirrhosis (due to fibrosis,
blockage of blood flow)?
Portal hypertension
Does the liver have the ability to regenerate?
Yes
What is the muscular sac located in depression
along surface of liver?
Gallbladder
What is the gallbladder used for?
Store & concentrate bile;
volume ~100 ml
What is the gallbladder lined by?
Simple columnar epithelium
with apical microvilli
What is the microvilli in the gallbladder used for?
Resorption of water
What does the gallbladder lack?
A muscularis mucosae
What is the lamina propria highly folded with?
Occassional tubuloalceolar mucus glands
What stimulates contraction of gallbladder?
CCK (Cholecystokinin)
What are components of bile?
Water, ions, electrolytes, cholesterol + phospholipids (= lecithin), bile acids (= bile salts) & bile pigments
What is the best known bile pigment?
Bilirubin
What is the non-sol breakdown product of Hb
Bilirubin
What happens in a failure to absorb bilirubin or failure to conjugate it and secrete?
accumulation of bile
pigments & jaundice
What does supersaturation of bile cause?
Gallstones (biliary calculi, cholelithiasis)
What does obstruction of bile ducts (choledocolithiasis) cause?
Bile stasis, or jaundice (icterus) if severe
What is chronic inflammation of the gallbladder?
Cholecystitis
What is the removal of the gallbladder?
Cholecystectomy
What happens following a cholecystectomy?
unable to concentrate bile; need to limit ingestion of fats
What is a highly lobulated gland with thin, connective tissue capsule, located in bend of duodenum?
Pancreas
What components does the pancreas have?
Endocrine and exocrine
Where is ductless endocrine pancreatic tissue located?
In islets of langerhans
Most of the pancreas is ______
Exocrine (i.e. with ducts) - a compound, acinar, serous gland
What is densely packed in the pancreas?
Serous acini contain pyramidal secretory cells surrounding a central lumen (duct)
What do acinar cells contain?
Zymogen granules (inactive enzyme precursors)
e.g., trypsinogen (=
protrypsin),
chymotrypsinogen (=
prochymotrypsin),
amylase, lipase
What are proteases?
Trypsin and chymotrypsin
What breaks down carbohydrates?
Amylase
What do lipases digest?
Lipids
Where do the secretory acini empty into?
Intercalated ducts
What can intercalated ducts differentiate into?
Add bicarbonate and water to pancreatic sections; neutralize acidic chyme from stomach -> optimal pH for pancreatic enzymes
What forms the beginning of intercalated ducts?
Duct cells
What is sometimes visible in the center of acini?
Centro-acinar cells
Where do intercalated ducts empty into?
Larger intralobular ducts
Where do intralobular ducts exit into?
Interlobular (=extralobular) ducts
How do pancreatic secretions enter the duodenum?
Via pancreatic duct at major duodenal papilla
What are the principle regulators of exocrine pancreas?
Polypeptide hormones secreted by enteroendocrine (APUD) cells
What is primarily secreted by stomach?
Gastrin
What secretes gastrin?
G cells of pyloric stomach
What does gastrin do?
Stimulates secretion of pancreatic fluid
What 3 things are secreted by duodenum?
Secretin
CCK
Enterokinase
What is secretin secreted by?
S cells
What does secretin do?
stimulates secretion of bicarbonate by cells of intercalated ducts
What is CCK (Cholecystokinin = pancreozymin) secreted by?
I cells
What does CCK do?
Stimulates acinar cells to secrete zymogen
What does enterokinase do?
converts trypsinogen -> trypsin (within small intestine), which converts chymotrypsinogen -> chymotrypsin (digests proteins)
What prevents the pancreas from digesting itself?
Cascade rxn
What is an autodigestion of pancreas brought on by alcoholism?
Pancreatitis
What does the cascade rxn break down?
Premature conversion of chymotrypsinogen to chymotrypsin & autolysis
Is severe, acute pancreatitis fatal?
Yes within hours
