Lecture 21: Liver

Question 1

Gross anatomical divisions of the liver

Answer 1

Liver divided into lobes by major divisions of portal vein/hepatic artery/hepatic vein.

Question 2

Liver microanatomy

Answer 2

Hepatocyte plates (rough hexagons) separate in/outflow. Portal triads at corners:
- Portal vein + hepatic artery mix -> sinusoidal capillaries -> central vein (inflow)
- Bile canaliculi -> bile ducts (outflow)

Question 3

Liver embryonic origin

Answer 3

Arises from endoderm foregut (also makes gall bladder, pancreas, bile duct), between dorsal/ventral mesentery.

Question 4

What happens to blood flow in portal hypertension?

Answer 4

Liver portal hypertension can cause backed up blood to anastamose around portal circulation.
- Esophageal varices: portal vein circulation goes elsewhere
- Anorectal varices: int. hemorrhoidal veins anasta. to iliac vein instead of sup. rectal vein.

Question 5

Space of Disse

Answer 5

Aka perisinusoidal space which drains into portal triad lymphatics. Separates sinus capillaries containing mixed hepatic/portal arteriovenous blood from LSECs.

Question 6

Liver lymphatic drainage

Answer 6

1. Thru space of Mall via portal triad lymphatics
2. Following central veins -> exit w/ hepatic vein
3. To pericapsular region, exits thru capsule

Question 7

Hepatocyte polarity

Answer 7

Apical: faces bile canaliculus
Lateral: tight junctions w/ other hepatocytes
Basal: faces space of Disse + sinus (sinusoidal caps.)
Hepatocytes have both basal and apical microvilli.

Question 8

Hepatocyte zonation

Answer 8

Zones are distinct in enzyme composition, oxygen tension, and blood metabolite concentrations.
Zone 1 = periportal
Zone 2 = in between
Zone 3 = pericentral

Question 9

Liver Sinusoidal Epithelial Cells

Answer 9

LSECs form a special endothelium lining hepatic sinuses. Functions:
- Endocytose blood waste products
- Coordinate liver immune cells
- Secrete hepatocyte GF + other cytokines
- APCs

Question 10

Special cells of the liver

Answer 10

• Kupffer cells (resident mφ’s)
• Hepatic stellate cells (aka perisinusoidal/Ito cells; Vit. A storage + fibrosis role)

Feet attach to perisinusoidal CT

Question 11

Where does the liver’s regenerative capacity come from?

Answer 11

Hepatocyte SCs in canals of Herring, which connect bile ductules with hepatocyte plates. SCs aka cholangiocytes. Also sense/modify bile composition and act in immune signaling.

Question 12

Liver fibrosis

Answer 12

Reversible fibrous accumulation due to aberrant ECM

Question 13

Cirrhosis

Answer 13

Irreversible, chronic liver fibrosis

Question 14

Steatosis

Answer 14

Intracellular fatty accumulation in hepatocytes; fatty liver

Question 15

Jaundice

Answer 15

Yellowing of skin due to deposition of excess bilirubin; sign of late stage liver disease

Question 16

Ascites

Answer 16

Abdominal distension due to peritoneal fluid; sign of late stage liver disease

Question 17

Fetor hepaticus

Answer 17

“Liver stink”; systemic blood shunting due to portal hypertension causes thiols to be expelled from the lungs.

Question 18

How does the liver act as an immune organ?

Answer 18

The liver produces most circulating innate immune proteins, including complement and opsonins. It also is the first organ exposed to antigens from the gut; antigens that pass through the liver thus tend to evoke tolerance e.g. liver transplants protective of other transplants.

Question 19

Embryonic development of the liver

Answer 19

Endoderm forms the hepatic and cystic diverticulum, which become the liver and gall bladder.

Question 20

Hepatic (classic) lobule

Answer 20

Structure centered around central veins with portal triads at corners (~hexagon)

Question 21

Portal lobule

Answer 21

Structure is centered around portal triad with central veins at vertices (~triangle)

Question 22

Hepatic acinus

Answer 22

Roughly 1 incoming central artery and its drainage area to 2 central veins.