Functional Histology of the Liver

Question 1

Blood flow through liver

Answer 1

• major blood supply = hepatic portal vein (70-75%)
  
  • minor = hepatic artery (25-30%) = branch from celiac trunks
• hepatic veins drain liver ==> inferior vena cava
  
  • vessel enter and leave @ “porta hepatis”

1. hepatic portal vein + hepatic artery ==> interlobular vessels
2. branching vessels of interlobular vessels ==> sinusoids ==> hepatocytes ==> central vein

Question 2

Lobules of liver

Answer 2

• liver lobules = smallest individual functional units w/in liver
• classical lobule
• portal lobule
• acinar lobule

Question 3

Characteristics of classic lobule

Answer 3

• ~hexagonal-shaped arrangement
• hepatocytes arranged radially around a central vein
• interlobular vessels (located @ “vertices” of lobule) carry incoming blood from:
  
  • hepatic portal vein (deoxy)
  • hepatic artery (oxy)
• bile ducts + space of Mall (lymphatic) also @ “vertices
  
  • bile secretion is separate via bile canaliculi

Question 4

Characteristics of portal lobule

Answer 4

• “portal lobule” = separate way of classifying same basic liver structure
• portal lobule = ~triangular shape between three central veins
  
  • = zone of tissue around a biel duct into which a group of bile canaliculi feed
  • = basic bile secretory fxnl unit

Question 5

Characteristics of acinar lobule

Answer 5

• another structural-fxnl definition
• “short axis” = between two portal triads
• “long axis” = between two central veins
• liver tissue in terms of blood delivery
• 3 “zones”

Question 6

Hepatocytes: structure/arrangement

Answer 6

• polyhedral in shape
• arranged in anastomosing plates or sheets with two sides facing the blood sinusoids (==> all hepatocytes exposed to plasma)
• surface area of the hepatocyte plasma membrane increased ~5-10 fold through extensive microvilli

Question 7

Fxns of hepatocytes

Answer 7

• storage of glucose as glycogen
  
  • @ fasting: glycogen ==> glucose ==> blood
• production of major blood proteins
  
  • albumin
  • clotting factors (e.g. prothrombin & fibrinogen)
• production of lipoproteins
  
  • VLDL (mainly), LDL, IDL and HDL
• produce bile
• conjugation of toxins

Question 8

Structure of bile canaliculi

Answer 8

• formed via apposed grooves in adjacent hepatocytes
• form circumferential belt around each hepatocyte ==> network of tubules running entirely within the hepatocyte plates
• tight jxns = prevent leakage of bile
• near portal triad: bile canaliculi ==> bile ductules (“canals of Hering”)

Question 9

Bile composition

Answer 9

• bile salts (= cholate derivatives)
• cholesterol, phospholipids, bilirubin glucoronides, and proteins + electrolytes
  
  • polymeric IgA

Question 10

Pathway/structure from bile ducts to Gall Bladder

Answer 10

• canals of Hering ==> interlobular bile ducts of portal triad
  
  • cubiodal epithelium ==> columnar as ducts fuse
• @ porta hepatis ducts form lobar ducts ==> form common hepatic duct
  
  • microvilli transport electrolytes and water
• common hepatic duct ==> cystic duct ==> gallbladder

Question 11

Pathway/structure of common bile ==> duodenum

Answer 11

• cystic duct + common hepatic duct ==> common bile duct
• pancreatic duct ==> common bile duct
• sphincters =
  
  • sphincter of choledochus/Boyden = before entry of pancreatic duct
  • sphincter of Oddi = after entry of pancreatic duct