Liver and Gallbladder

Question 1

Functions of the liver

Answer 1

1. Synthesis of circulating plasma proteins 2. Storage and conversion of several vitamins (A,D,K) and iron 3.Degradation of drugs and toxins 4. Important metabolic pathways: glycogen storage, cholesterol metabolism, urea synthesis 5. Bile production (exocrine fx): delivered to duodenum, act as emulsifying agents to aid gut absorption 6. Endocrine-like functions: modifies hormones

Question 2

Blood supply to the liver: hepatic portal vein

Answer 2

• Supplies approx. 75% of liver’s blood volume - Blood is rich in nutrients and toxic materials from intestine, blood cell breakdown products from spleen, and endocrine secretions - Venous blood is largely depleted of oxygen

Question 3

Blood supply to the liver: hepatic artery

Answer 3

• Carries oxygenated blood - Blood mixes with the venous blood just before entering the hepatic sinusoids - Supplies approx. 25% of liver’s blood volume - Branches irrigate structures in portal canal

Question 4

Portal triad

Answer 4

• Hepatic artery, portal vein, bile duct - Present in Glisson’s capsule at the angles of hexagonal liver lobule

Question 5

Blood flow through the liver (sinusoid pathway)

Answer 5

Hepatic portal vein –> hepatic sinusoids (like capillaries) –> central vein –> sublobular vein –> (joins) hepatic veins –> IVC

Question 6

Structural components of liver

Answer 6

• Parenchyma: one cell thick plates of hepatocytes separated by sinusoid capillaries - CT stroma: continuous with Glisson’s capsule, branches into small portal canals - Sinusoidal capillaries (sinusoids): separate plates of hepatocytes - Perisinusoidal spaces (spaces of Disse): lie between sinusoidal epithelium and hepatocytes

Question 7

Classic liver lobule

Answer 7

• Hexagon with central vein at center - Visualized by drawing lines connecting the portal canals around a central vein - Other species have CT around lobules

Question 8

Portal lobule

Answer 8

• Emphasizes the exocrine fx of liver (bile secretion) - Portal canal at center - Triangle formed by connecting lines between the three closest central veins

Question 9

Liver acinus

Answer 9

• Emphasizes blood secretion - Football shape whose long axis is a line between two central veins and short axis is between adjacent portal canals that lie between central veins - Zone 1: first to receive oxygen, nutrients, toxins from blood, die last when blood flow blocked and first to regenerate - Zone 2: intermediate - Zone 3: first to show ischemic necrosis and fat accumulation

Question 10

Hepatic sinusoids

Answer 10

• Discontinuous sinusoid capillaries with large gaps between neighboring cells - Part of wall has Kupffer cells

Question 11

Kupffer cells

Answer 11

• Part of the wall of sinusoids - Derived from monocytes, members of mononuclear phagocytic system (MPS) - Destroy bacteria and aged RBC - Digest hemoglobin - Make up 15% of liver cell population

Question 12

Space of Disse (perisinusoidal space)

Answer 12

• Site of exchange of materials between blood and liver cells - Microvilli of hepatocytes project into this area - Where ito cells reside

Question 13

Ito cells

Answer 13

• Reside in the space of Disse - Primary storage site for hepatic vitamin A - Chronic inflammation or cirrhosis: Lose storage ability and transform into myofibroblasts that synthesize collagen –> liver fibrosis

Question 14

Describe hepatocytes

Answer 14

• Large, polygonal (6+ sides) with diameter of 20-30 microns - 80% of liver cell population - Nuclei are large, spherical, centrally located - Adult liver has mostly tetraploid cells - Long life span (about 5 months), regenerative ability decreases with age - Cytoplasm: many mito, elaborate Golgi, highly developed ER, many peroxisomes, lysosomes and glycogen

Question 15

Neonatal hyperbilirubinemia

Answer 15

• When newborns have underdeveloped sER - Bilirubin is not converted to bilirubin glucuronide - Tx with fluorescent bulbs that transform unconjugated bilirubin to photoisomer

Question 16

Biliary Tree: Flow of Bile

Answer 16

Bile flows from center of classic liver lobule –> gallbladder –> small intestine Bile canaliculi are small canals between hepatocytes –> empty into intrahepatic ductules (canals of Hering) within lobule –> join with interlobular bile ducts

Question 17

How much bile is secreted per day? What increases bile secretion? What are the contents of bile?

Answer 17

• Liver secretes about 1 liter of bile/day - Increased by CCK, gastrin, motilin from enteroendocrine cells, PNS stimulation - Consists of water, phospholipids, cholesterol, bile salts (aid in digestion and absorption), bile pigments, electrolyes

Question 18

Bilirubin glucuronide

Answer 18

• Bile pigment that comes from hemoglobin breakdown - Excrete with feces –> provides color

Question 19

What is the gallbladder?

Answer 19

• A hollow, pear-shaped organ that can hold about 50ml - Single duct (cystic duct) - receives diluted bile from the liver and discharges concentrated bile to the duodenum (via common bile duct and Sphincter of Oddi)

Question 20

Histology of the gallbladder

Answer 20

• Mucosa: simple columnar epithelial cells with microvilli, and lateral plications (tucks that shorten structure). Has lamina propria but NO muscularis mucosae - Mucosa of empty gallbladder has rugae (folds) - flatten out when full. Invaginations form diverticula (Rokitansky-Aschoff sinuses) - can extend into muscularis (increase with age) - Muscularis: random smooth muscle bundles, contraction empties contents into cystic duct - Adventitia attaches liver to gallbladder, also has serosa on free surface