Histology - Liver, Gallbladder, & Pancreas

Question 1

Liver/Lobule Anatomy

Answer 1

o Glisson’s Capsule – thin connective tissue capsule covering the surface
• Portal triad – found at periphery of lobule in corners
o Contains bile duct, branch of hepatic artery, branch of portal vein (largest)
o Bile duct contains cuboidal cells with visible nuclei
o Bile and lymph runs in OPPOSITE DIRECTION from blood flow
• Central vein – collects blood from sinusoids and goes to hepatic vein
• Hepatic plates
• Sinusoids – capillaries with fenestrations allowing blood passing through to mix with surrounding hepatocytes

Question 2

View/Classifications of Liver Lobules

Answer 2

 Classic – point of focus is central vein with portal triad in periphery
 Portal – point of focus is portal triad with central vein in periphery
 Acinus – point of focus is septum between lobules with central vein in periphery
• Pathologists use this view
• Zone 1 – maximum availability of O2, nutrients, and toxins
• Zone 3 – furthermost from distributing vessel (closest to central vein); lowest availability of O2, nutrients & toxins; often 1st to die

Question 3

Liver Blood Supply and Lymph Flow

Answer 3

o Blood Supply – 25-30% of total cardiac output
 Portal vein (75% of hepatic blood) – deoxygenated; full of digestive products (NO LIPIDS) from intestines via SMV; hemoglobin breakdown products from spleen and endocrine products from pancreas via splenic vein
 Hepatic artery (25% of hepatic blood) – O2
 Hepatic vein – Central vein
• Drains to right, middle, or left hepatic vein before joining IVC
o Lymphatic Drainage - hepatic lymph is unique in that it is rich in plasma protein
 Space of Disse – space between sinusoids and hepatocytes that filters blood

Question 4

Hepatic Sinusoids

Answer 4

o Sinusoidal capillaries lined w/ discontinuous endothelium carries blood towards central vein
o Space of Disse – bathes hepatocytes with sinusoidal plasma and initiates lymph formation
o Cells within sinusoids:
 Kupffer cells – macrophages located between endothelial cells; phagocytic
 Lipocytes – store lipid and vitamin A

Question 5

Limiting Plate

Answer 5

– located at periphery of lobule; hepatocytes surrounds the circumference forming a nearly continuous wall of hepatocytes against the interlobular septum

Question 6

Hepatocyte Microstructure

Answer 6

 Large polyhedral parenchymal cells (20 – 30 microns)
 One or two nuclei
 Cytoplasm abundant in mitochondria
 Plasma membrane
• Between hepatocytes are tight and gap junctions with neighboring cells
• Bile canaliculi formed by indentations of plasma membrane

Question 7

Hepatocyte Ultrastructure

Answer 7

o Ultrastructure Detail
 RER – produces plasma proteins (albumin, clotting factors, lipoproteins)
 SER – bilirubin conjugation, bile salt synthesis, detoxification
 Golgi – packages proteins for release into Space of Disse
 Peroxisomes – contains oxidases and catalases
 Microvilli extend into space of Disse and increase absorptive surface

Question 8

Bile Contents

Answer 8

o 82% water
o 12% bile acids (cholic and chenodeoxycholic acids)
o Bilirubin, cholesterol, electrolytes

Question 9

Biliary Tract (intra and extrahepatic)

Answer 9

o Intrahepatic – bile canaliculi (NO CELLS, tight junctions)  Canals of Hering (crosses limiting plate)  bile ducts in portal triads; lined by simple cuboidal epithelium
o Extrahepatic – lined by simple columnar epithelium
 Hepatic duct – right and left join to form common hepatic duct
 Cystic duct – drains gallbladder; joins common hepatic duct to form common bile duct
 Common bile duct – joins main pancreatic duct to form ampulla of Vater
 Sphincter of Oddi – controls opening of ampulla of Vater into duodenum

Question 10

Gallbladder

Answer 10

o Function – stores30-75ml of concentrated bile
 Hepatic bile is isotonic; gallbladder absorbs water and concentrates bile up to 5x
o Structure
 Simple columnar epithelium (NO goblet cells)
 Surface microvilli and basolateral active Na+ pumps; pump into blood (H20) follows
o Cholecystokinin – controls bile excretion
 Hormone secreted by enteroendocrine cells in duodenum
 Stimulated by presence of ingested fats and amino acids

Question 11

Pancreas Function & Anatomy & Ducts

Answer 11

-Function
 Exocrine (90%) – synthesis and secretion of digestive enzymes; 2-2.5 liters a day
 Endocrine (10%) – organized into Islet of Langerhans; secretes hormones into blood
-Anatomy – retroperitoneal
 Head of pancreas located in duodenal concavity
-Main Pancreatic Duct (duct of Wirsung)
 Begins in tail and continues entire length
 Fuses with common bile duct to form ampulla of Vater at entry to duodenum
 Lined by simple columnar epithelium

Question 12

Exocrine Pancreas

Answer 12

• Contains groups of acini within lobules that produce, store, and release enzyme products into intralobular ducts that flows into larger ducts
• Centroacinar cells found in lumen of acini are distinguishing characteristic of exocrine pancreas
• Large reserve of function; more than 90% of cells must be damaged before problems arise
 Intercalated ducts – carries secretory products to bile duct
 Synthesis and Secretion – fluid secreted is isotonic and alkaline with pH > 8
• Pancreatic enzymes (made by acinar cells) – identified as zymogen granules are located in apical side of cell; RER located on basal side of cell
• Water & Electrolytes (made by ductular cells)
o Alkaline fluid, rich in HCO3-
o Helps neutralize acidic chyme

Question 13

Control of Exocrine Secretion

Answer 13

• Hormones secreted by enteroendocrine cells of duodenal and jejuna mucosa in response to ingested food and pH of gastric chyme
o Fat rich food  CCK stimulates enzyme-rich secretion by acinar cells
o Acidic chyme  secretin  watery, HCO3- secretion by ductal cells
• Vagus nerve

Question 14

Striated Ducts

Answer 14

• Parotid gland contains striated ducts, Pancreas does NOT contain striated ducts

Question 15

Endocrine Pancreas & Cell Types

Answer 15

– Islet of Langerhans
 Capsule separates islets from surrounding exocrine pancreas
 Cell Types
•A – Alpha cells – glucagon; increases blood glucose levels
o 20% of islet cells
o Peripherally located in islet
•B – Beta cells – insulin; decreases blood glucose levels
o 70% of islet cells
o Centrally located
o Contains proinsulin  insulin + C peptide (both secreted into blood)
•D – Delta cells – somatostatin; inhibit other islet cells (paracrine effect) and slow motility of GI tract to extend time for digestion and uptake of nutrients
o 5% of islet cells
PP (or F cells) – pancreatic polypeptide – rare cell; varies in function

Question 16

Cholecystectomy

Answer 16

– removal of gallbladder

Question 17

Cholelithiasis

Answer 17

– calcium deposits on cholesterol lipids and harden; can cause obstructive jaundice, cholecystitis, pancreatitis or other problems

Question 18

Primary sclerosing cholangitis

Answer 18

– involves ongoing inflammation, destruction and fibrosis of intra- and extraheaptic bile ducts; leads to cirrhosis, portal hypertension, and liver failure

Question 19

Acute pancreatitis

Answer 19

• 10% mortality rate; autodigestion due to activated enzymes; diagnose via certain enzymes that leak into blood

Question 20

Cystic fibrosis

Answer 20

– 90% rely on pancreatic enzyme supplements to relieve symptoms of exocrine pancreatic insufficiency due to chronic pancreatitis
 Progressive pancreatic damage due to ductal clogging resulting in dilated (cystic) ducts with surrounding fibrosis)

Question 21

Diabetes

Answer 21

– increased blood glucose levels
 Type I – autoimmune destruction of Islet of Langerhan cells resulting in loss of beta cells
 Type II – decreased sensitivity of tissues to insulin (insulin resistance) resulting in normal/elevated insulin levels/secretion

Question 22

Insulinoma

Answer 22

– form of cancer involved B cells; tumors can be functional resulting in unregulated hypersecretion and symptoms of hypoglycemia

Question 23

Pancreatic carcinoma

Answer 23

– usually spread to liver due to pancreas close association with large blood vessels, extensive drainage to lymph nodes, and frequent spread via portal venous system