Liver, Gallbladder, Pancreas

Question 1

Liver

Gross Anatomy

Answer 1

• Four lobes: right, left, quadrate, caudate
• Porta hepatis located in concave inferior surface
  
  • branches of hepatic portal vein and hepatic artery enter
  • right and left hepatic ducts exit
  • lymphatics leave
• Dual blood suppy:
  
  • Hepatic artery proper
    
    • oxygenated blood
  • (Hepatic) Portal Vein
    
    • oxygen poor blood from GI tract, pancreas, and spleen
  • Sources mix at liver sinusoids
  • Leaves liver via hepatic veins
    
    • Near superior surface of liver
• Covered by mesothelium except in 2 places:
  
  • where directly contacts gallbladder
  • bare area where mesothelium → underside of diaphragm
• Glisson’s capsule
  
  • Dense irregular CT deep to mesothelium
  • continuous with capsule around vessels and bile ducts entering liver

Question 2

Classic Liver Lobule

Answer 2

Based on venous drainage.

Region whose sinusoids all drain into same centrain vein.

• Hexagonal in cross section
• Portal triads located in portal canals @ each vertex
• Central vein (terminal hepatic venule) @ center
• Blood flows from periphery towards center
• Bile flow from center out

Question 3

Portal Triad

Answer 3

• Located within portal canal
  
  • Enclosed by the limiting plate of hepatocytes
• Components:
  
  • Hepatic artery/arteriole
  • Portal vein/venule
  • Bile duct (simple cuboidal epithelium)
  • Lymphatic capillaries often present

Question 4

Central Veins

Answer 4

Terminal Hepatic Venule

• Thin wall with endothelial cells but no smooth muscle
• Plates of hepatocytes organized radially around central vein
• Hepatic sinusoids run between plates
• Receives blood from sinusoids
• Drain into sublobular veins
• Distinguished from portal triad because:
  
  • not accompanied by other vessels/ducts
  • less surrouding CT

Question 5

Hepatic Sinusoids

Answer 5

• Highly permeable sinusoidal capillaries
• Wall formed by mixture of endothelial cells and Kupffer cells
• Blood from inlet branches of hepatic artery and portal vein mixes here

Question 6

Kupffer Cells

Answer 6

• Hepatic resident macrophage
• Contributes to sinusoidal walls
  
  • May extend across lumen
• Phagocytize old/damaged RBC and particulates

Question 7

Space of Disse

Answer 7

• Narrow space encircling each sinusoid
  
  • Seperates it from hepatocytes
• Microvilli of hepatocytes extend into space of Disse
• Location of most metabolic exchange between blood and hepatocytes
• Reticular fiber stroma located mainly here

Question 8

Ito Cells

(Hepatic Stellate Cells)

Answer 8

• Located in the space of Disse
• Stores Vit A in cytoplasmic lipid droplets
• Produces the reticular fiber stroma of liver
• In cirrhosis, produce collagen type I causing fibrosis

Question 9

Hepatic Blood Flow

Answer 9

Interlobular branches of hepatic artery & portal vein in portal canals →

Distributing branches leave portal canal & run between classic lobules →

Inlet vessels enter lobules →

Sinusoids →

Central vein →

Sublobuler vein →

Larger collecting veins →

3 or more hepatic veins →

IVC

Question 10

Portal Lobule

Answer 10

Based on bile flow.

Region whose bile canaliculi all drain toward the bile duct in the same portal canal.

• Roughly triangular in cross section
• Central vein at each vertex
• Portal triad in the center
• Bile flows from periphery towards center

Question 11

Hepatic Acinus of Rappaport

Answer 11

Based on gradients of O₂, nutriends, and tonxins supplied by distributing vessels.

Used to explain patterns of hepatocyte metabolism and pathology.

• Diamond shaped in cross section.
• Central veins and portal triads located at the periphery.
• Long axis connects 2 central veins
• Short axis connects 2 portal triads
• Distributing vessels lie on the short axis
• Consists of 3 zones centered around the distributing vessels

Question 12

Hepatocytes

Answer 12

• Epithelial cells
• Major parenchymal cell of the liver
• LM:
  
  • Polygonal cells with round, euchromatic nuclei
  • One or more prominent nucleoli
  • Often binucleate or polypoid
• Plasma membrane has 2 structurally and functionally different domains:
  
  • Sinusoidal domain
    
    • Contacts the space of Disse
    • Endocrine face
  • Lateral domain
    
    • Site where bile canaliculi form
    • Exocrine face

Question 13

Bile Canaliculi

Answer 13

• Formed from plasma membranes of adjacent hepatocytes
• Tight junctions prevent bile leakage
• Golgi, lysosomes, and residual bodies of hepatocytes often located near canaliculi
• Lipofuscin may accumulate within residual bodies

Question 14

Bile Ductules

Answer 14

Intrahepatic ductules, canals of Hering, cholangioles.

• Found near the periphery of a classic lobule
• Lined by simple cuboidal epithelial cells
• Pierce the limiting place
• Drains into interlobular bile ducts

Question 15

Enterohepatic Recirculation

Answer 15

• Bile salts recirculate between liver and small intestine
• Pathway
  
  • Hepatocyte
  • Bile canaliculi
  • Bile duct system
  • Duodenum
    
    • Some lost in feces
  • Resoption into intestinal blood vessels
  • Hepatic portal vein
  • Hepatic sinusoids
  • Space of Disse
  • Hepatocyte

Question 16

Deficiency of Bile Salts

Answer 16

• Can lead to malabsorption of some fats
• Results in steatorrhea
• Precipitation of cholesterol in bile can lead to cholelithiasis

Question 17

Biliary Tree

Answer 17

• Intrahepatic channels
  
  1. Bile canaliculi
  2. Bile ductules
  3. Interlobular bile ducts
• Extrahepatic ducts
  
  1. Right and left hepatic ducts
     
     • Leave liver at porta hepatis
  2. Common hepatic duct
  3. Cystic duct from gallbladder
  4. Common bile duct
• Common bile duct unites with the main pancreatic duct
• Forms the ampulla of Vater
• Empties into duodenum at the major duodenal papilla
  
  • sphincter of Oddi

Question 18

Gallbladder

Functions

Answer 18

• Stores and concentrates bile
• Releases stored bile via cystic duct into common bile duct
  
  • CCK main stimulus for bile release
    
    • Secreted by I cells in intestinal mucosa
      
      • In response to dietary fat in intestine

Question 19

Gallbladder Wall

Answer 19

Has a mucosa, muscularis, and serosa/adventitia.

No muscularis mucosae or submucosa.

• Mucosa
  
  • Simple columnar epithelium
    
    • mainly absorptive cells
    • lateral spaces between absorptive cells widen when actively concentrating bile
  • Lamina propria
  • Unless gallbladder is full, mucosa usually has many deep irregular folds
• Muscularis
  
  • Circular near neck of bladder
  • More irregular in body
• Serosa/Adventitia
  
  • Adventitia is present where gallbladder directly contacts liver
  • Serosa covers remainder of the organ

Question 20

Rokitansky-Aschoff Crypts

Answer 20

• Deep invaginations of the epithelium
• Extends into or through muscularis
• Found in the gallbladder with chronic inflammation
• May perforate

Question 21

Pancreatic Acinar Cells

Answer 21

• Pyramid-shaped serous cells
• Secrete wide variety of digestive enzymes zymogens
  
  • Trypsinogen
  • Chymotrypsinogen
  • Procarboxypeptidase
• Basal basophilia due to extensive RER
• Acidophilic zymogen granules in apical cytoplasm stores enzymes
• Exocytosis occurs in response to signals
  
  • CCK
  • ACh from vagal fibers

Question 22

Centroacinar Cells

Answer 22

• Pale, low cuboidal cells
• Unique to the pancreas
• Lies within the lumen of a secretory acinus
• Represents the first cells in an intercalated duct
  
  • Intra-acinar portion

Question 23

Pancreatic

Intercalated Ducts

Answer 23

• Smallest type of intralobular duct
• Simple, low cuboidal epithelium
• Secretes a watery bicarbonate-rich fluid
  
  • In response to secretin
    
    • Hormone produced by S cells in duodenum
• Drains into larger intralobular ducts

Question 24

Pancreatic Ductal System

Answer 24

• Centroacinar cells → first cells in an intercalated duct
• Intercalated ducts
• Larger intralobular ducts
  
  • Lined by simple cuboidal epithelium
  • No basal striations
    
    • No striated duct in the pancreas
  • Empty into interlobular ducts
• Interlobular ducts
  
  • Run in the CT septa
  • Empty into the main pancreatic duct
• Main duct
  
  • Units with common bile duct
  • Form the ampulla of Vater
  • Empties into duodenum at the major duodenal papilla

Question 25

Islets of Langerhans

Answer 25

* **Endocrine** portion of the pancreas * Spherical structures scattered among acini * Most islets **larger** than a secretory acinus * Usually **paler** staining * Highly vascularized with **fenestrated capillaries** * Cells appear more **irregularly arranged** * Not structurally polarized

Question 26

𝛽-cells

Answer 26

* Most abundant cell in islets of Langerhans * Main product is **insulin** * Also produce other hormone * Amylin appetite suppresant * Located throughout islet in humans * Secretory granules may have dark angular "crystalline" core

Question 27

**𝛼-**cells

Answer 27

* Produce glucagon * Mainly located at the periphery of an islet * Granules have a dark spherical core surrounded by a clear halo

Question 28

𝛿-cells | (Delta)

Answer 28

* Produce **somatostatin** * Functions to inhibit: * gut motility * gallbladder secretions * secretions by acinar cells * secretions of insulin and glucagon * Granules are **light-staining & almost completely filled** with secretory material

Question 29

PP (F) Cells

Answer 29

* Produce **pancreatic polypeptide** * Inhibits secretion by acinar cells and duct cells * Stimulates gastric chief cells

Question 30

Zollinger-Ellison Syndrome

Answer 30

* Pancreatic tumor cells produce excess gastrin * Cause excessive acid secretion from the stomach * Leads to ulcers * Gastrin produced transiently in islets during fetal life.

Question 31

Epsilon Cells

Answer 31

Produce Ghrelin → appetite suppresant

Question 32

Insuloportal System | (Islet-acinar Portal)

Answer 32

Venous portal system within the pancreas. Carries islet hormones that affect activity of other islet cells or acinar cells. * **First capillary bed within islets** * **Fenestrated** * Blood flows from periphery to center of an islet * Venules drain first capillary bed * **Secondary capillary bed supplies acini** * **Continuous** * Acinar cell activity can be modulated by islet hormones