Microanatomy: liver and gallbladder

Question 1

Components of the liver lobule 1

Answer 1

• Each lobule is roughly hexagonal w/ portal triads (hepatic arteriole, portal venule, bile duct) at each vertex
• In the center of the lobule there is the central vein, into which the hepatic arteriole and portal venule dump blood (via sinusoids)
• Portal triad: portal venule is largest and has thin wall (more likely to see RBCs), hepatic arteriole is very small and has endothelial cell nuclei extending into lumen and surrounded by SmM, bile duct wall is simple cuboidal and lumen is medium size

Question 2

Components of the liver lobule 2

Answer 2

• Surrounding each sinusoid there is a layer of hepatocytes and other cells (hepatocyte plate)
• Rows of hepatocytes run from the outer edges of the lobule to the central vein
• Sinusoids are capillaries that run from the portal vein/hepatic artery thru rows of hepatocytes to central vein
• Sinusoids are fenestrated discontinuous capillaries (lined by endothelial cells) and contain residential macrophages (kupffer cells)

Question 3

Flow of blood and bile thru liver 1

Answer 3

• One source of blood is the hepatic artery (25%), which is oxygen rich and nutrient poor
• Hepatic artery-> interlobar a-> interlobular a-> hepatic arterioles-> sinusoids
• Another source of blood is the portal vein (75%), which is oxygen poor and nutrient rich
• Portal vein-> interlobar v-> interlobular v-> hepatic venule-> sinusoids
• Blood from portal triad (either hepatic arterioles or venules) turns 90 deg, flows down the sinusoid, and turns 90 deg into the central vein (which takes blood to sublobular veins-> hepatic vein-> IVC)

Question 4

Flow of blood and bile thru liver 2

Answer 4

• Blood in the sinusoids are mixed, containing both hepatic arteriole and venule blood
• Overall, blood flows from portal triad toward central vein thru sinusoids (out->in)
• Bile has the opposite flow direction: it is made in hepatocytes and flows away from the central vein, first thru bile canaliculi, then to canals of Hering
• Canals of Hering conduct bile to the bile ducts of the portal triad, which takes the bile duct to larger hepatic ducts
• Overall bile flows from in->out

Question 5

3 ways to view liver lobule 1

Answer 5

• Classic lobules: central vein in middle and six portal triads in a hexagon around the vein
• Portal lobules (bile flow): triangular shape w/ central veins at the 3 apices of the triangle and one portal triad in the middle
• In this view the blood flows form in->out (from triad to central veins) and bile flows from out->in (from hepatocytes to portal triad)
• Rappaport lobules (blood flow): are oval shaped, w/ central veins being at the two long ends of the oval and portal triads being at the two short ends of the oval

Question 6

3 ways to view liver lobule 2

Answer 6

• The oval is broken into 3 zones, zone 1 extending from the two portal triads (in middle of oval) and zone 3 at the very (long) ends of the oval (area btwn portal triad and central vein)
• Zone 1 is most oxygen rich (get blood from triads first), most metabolically active, and first to be assaulted by toxic substances
• Zone 3 (most oxygen poor b/c farthest from portal triad- closest to central vein) is first to undergo hypoxic injury

Question 7

Hepatocyte plate 1

Answer 7

• Components are: hepatocyte, sinusoid, kupffer cell, Ito cell, space of disse
• Hepatocytes have numerous organelles, have many basolateral surfaces that face a number of sinusoid-hepatocyte spaces (space of disse)
• These surfaces have abundant microvilli that project into space of disse (space under endothelial cells lining the sinusoids, and above the hepatocyte basolateral membranes)

Question 8

Hepatocyte plate 2

Answer 8

• The surfaces of hepatocytes that face the bile canaliculi (lateral surfaces of neighboring hepatocytes that form grooves for bile to be secreted and travel thru) have many tight junctions btwn cells, and some microvilli projecting into the canaliculli
• The sinusoids are discontinuous and fenestrated, and contain kupffer cells (macrophages)
• Space of disse: perisinusoidal space where nutrient exchange w/ hepatocytes occurs
• Ito (stellate) cells: reside in space of disse and are storage sites for vit A, and fat, and produce collagen

Question 9

Gallbladder

Answer 9

• Function: concentrate, store, and release bile
• Muscular wall of galbladder (4 layers) stimulated to contract by CCK
• Mucosa: simple columnar epithelium and lamina propria (highly vascularized), is highly convoluted when empty (no goblet cells, no muscularis mucosa, no submucosa)
• Muscle layer: thin layer of SmM in an oblique orientation
• Connective tissue layer: dirCT w/ nerves and vessels
• Serosa covering (or adventitia where it is attached to liver)

Question 10

Gallbladder vs SI

Answer 10

• NO VILLI in gallbladder, branching folds as outpouchings of mucosa (no lacteal or SmM as in SI)
• No goblet cells in mucosa
• No muscularis mucosa or submucosa
• SmM cells are arranged obliquely instead of organized in the same direction, and are closer to lamina propria (in gallbladder)