Histology: Liver, Pancreas Gallbladder

Question 1

Histological Organization of Liver

Answer 1

3 Types of Functional Units:

Classic Lobule:

• Hexagonal unit emphasizing anatomical organization

Portal Lobule

• Emphasizes exocrine function (bile)

Liver Acinus

• Emphasizes blood perfusion and metabolic activity

Question 2

Classic Lobule

Answer 2

• Anatomosing plates of hepatocytes
  
  • Hepatic Sinusoids inbetween (sinusodoial capillaries)
• Central vein (receives blood)
• Portal Space
  
  • Portal triad
    
    • ​Hepatic Artery
    • Bile Duct
    • Portal Vein
• Separated by CT septa (clearly defined in other animals)

Question 3

Portal Triad

Answer 3

• Venule
  
  • Branch of portal vein
• Arteriole
  
  • Branch of hepatic artery
• Bile ductule (1 or 2)
  
  • Branch of bile duct
  • Cuboidal epithelium
• Lymphatic capillaries
• Nerves

Question 4

Blood Flow through Liver Lobule

Answer 4

• Hepatic artery
  
  • Oxygenated blood to liver (minority)
• Portal Vein
  
  • Majority of blood to liver
• Both dump blood into sinusoids
  
  • Mixed blood
• Dumped into central veins
  
  • All converge to hepatic veins which empty to vena cava

Question 5

Portal Lobule

Answer 5

• Emphasizes exocrine function of liver
• Portal triad at center
  
  • ​Hepatocytes produce bile, which flows to center of portal lobule (bile duct)

Question 6

Liver Acinus (diamond shaped)

Answer 6

• Emphasizes blood perfusion and meatbolic activity
• Zone 1:
  
  • ​Closest to where blood enters
  • Most highly oxygenated blood
  • Lowest level of metabolites
  • Last cells to die, first to regenerate
• Zone 2:
  
  • ​Intermediary zone
• Zone 3:
  
  • ​Least oxygenated blood
  • Highest levels of metabolites
  • First cells to die, last to regenerate

Question 7

Hepatocytes

Answer 7

• Large polyhedral cells with short microvilli
• Acidophilic cytoplasm
  
  • Often binucleated
• Lives 5 months
• Capable of regenerating

Hepatic Sinusoids (blood vessel):

• In between hepatocytes
• Discontinuous endothelial lining
• Discontinuous basal lamina

Kupffer Cells

• Stellate sinusoidal macrophages
• Located in sinusoidal endothelium
• Derived from monocytes
• Appear black in H&E?

Question 8

Perisinusoidal Space

Answer 8

• Space between hepatocytes and endothelium
  
  • Exchange of materials between blood and liver cells
• Hepatocyte microvilli project into space
  
  • Increase surface area for exchange

Ito Cell

• Stores Vitamin A and fat soluble vitamins
• Can differentiate into myofibroblasts under pathological conditions
  
  • Hepatic Fibrogenesis (from collagen deposits)
  • Increase vascular reistance resulting in portal hypertension

Question 9

Bile Production

Answer 9

• Major exocrine function of liver
  
  • Produced by SER
  • 1 L/day
• Secreted into bile canaliculi
  
  • ​Furrows between adjacent hepatocytes
  • Tight junctions

Question 10

Intrahepatic Biliary Ducts

Answer 10

• Canaliculi become canals of hering lined by cholangiocytes
  
  • These converge to from intrahepatic bile ductules
  • Formation of interlobular bile ducts
    
    • Located in portal triads
    • Join to form right/left hepatic ducts

Question 11

Bilirubin

Answer 11

• Product of hemoglobin breakdown
• Modified by SER and secreted into bile canaliculi
  
  • Excreted in feces
• Jaundice: failure to excrete bilirubin
• Neonatal hyperbilirubinemia
  
  • Underdeveloped SER in newborns
  • Tx: blue light

Question 12

Gallbladder

Answer 12

• Mucosa
  
  • ​Simple columnar epithelium with microvilli
  • Lamina Propria: mucin-secreting glands
  • No muscularis mucosae
• No submucosa
• Muscularis Externa
  
  • ​Randomly oriented
• Adventitia
  
  • ​Deep Surface (in contact with liver)
• Serosa
  
  • ​Superficial surface

Fat in the duodenum stimulates secretion of CCK from enteroendocrine cells

• CCK stimulates contraction of gallbladder and release of bile into duodenum

Question 13

Gallstones

Answer 13

• Cholelithiasis
• Pain referred to:
  
  • RUQ (T6-T9 dermatomes)
  • Right shoulder (if inflamation affects diaphragm)
• Risk Factors:
  
  • Five F’s (female, fair, fertile, fat, fourty)

Question 14

Pancreas

Answer 14

Exocrine Pancreas:

• Majority of pancreatic tissue
• Made of pancreatic acini

Endorcrine Pancreas:

• Minority of pancreatic tissue
• Made of pancreatic islet

Question 15

Exocrine Pancreas

Answer 15

• Compound (branching duct system) acinar gland
• Pancreatic acinar cells
  
  • Basophilic basal cytoplasm
  • Eosinophilic apical cytoplasm
• Secrete digestive enzymes
  
  • In inactive form, activated in lumen of duodenum
  • Stimulated by cholecystokinin (CCK)

Centroacinar Cells

• Located at beginning of duct system

Intercalated Ducts:

• Secrete bicarbonate (neutralizes acid from chyme) and water
  
  • ​Stimulated by secretin

Question 16

Pancreatitis

Answer 16

• Inflammation of pancreas
• Causes:
  
  • Gallstones
  • Alcoholism
  • Infection
  • Drugs
  • Trauma
• Acute Pancreatitis:
  
  • Proenzymes becomes active and digest pancreatic tissue
• Chronic Pancreatitis:
  
  • progressive fibrosis and loss of pancreatic function

Question 17

Endocrine Pancreas

Answer 17

• Pancreatic islets
  
  • Variable size
  • Surrounded by thin reticular capsule
  • Pale-staining

Alpha-Cells:

• 15-20% islet
• Located at periphery
• Secrete glucagon

Beta-Cells

• 60-70%
• Center of islet
• Secrete insulin

Delta-Cells:

• 5-10%
• At periphery
• Secrete somatostatin

Question 18

Diabetes Mellitus

Answer 18

Type 1 Diabetes

• Insulin-dependent
• Autoimmune destruction of beta-cells
  
  • Absence or inadequate insulin amounts

Type 2 Diabetes

• Non-insulin dependent
• Insulin resistance
  
  • Beta-cells initially increase production but cannot sustain adequate levels over time