liver histology

Question 1

1. Describe the basic pattern of blood flow through the liver

Answer 1

Liver receives the majority (70-75%) of its blood supply from the hepatic portal vein and about 25-30% from the hepatic artery which branches from the celiac trunk. The hepatic veins drain the liver, emptying into the inferior vena cava. These vessels and the bile duct enter and leave the liver in a hilar region called the porta hepatis.

Question 2

Functions of liver

Answer 2

It synthesizes most of the blood proteins, glycoproteins, and lipoproteins, stores glucose from the gut temporarily in the form of glycogen, metabolizes many lipid-soluble molecules and toxins, and is involved in urea formation. Also production of bile

Question 3

List the three lobular descriptions of the basic microstructural organization of the liver.

Answer 3

Classical lobule, portal lobule and acinar lobule. The lobules are the smallest individual functional units within the liver

Question 4

Structure of classic lobule

Answer 4

Hexagonal arrangement of anastomosing hepatocytes arranged radially around a central vein. At each of six vertices is a bile duct, a lymphatic space (space of mall) and interlobular vessels carrying deoxygenated blood from hepatic portal vein and oxygenated blood from hepatic artery. Distributing or perilobular branches from interlobular vessels extend peripherally around edges of lobules distributing blood into sinusoids btw plates of hepatocytes

Question 5

what is the portal triad

Answer 5

The interlobular vessels (venules and arterioles) and bile duct surrounded by loose CT stroma

Question 6

Describe blood flow in classic lobule

Answer 6

Blood from the perilobular branches is distributed into sinusoids btw plates of hepatocytes. Blood percolates through the narrow sinusoids between the plates, en route to the central vein.

Question 7

How thick are the hepatocyte plates in classic lobule

Answer 7

one hepatocyte thick

Question 8

Bile flow in classic lobule

Answer 8

A network of tiny bile canaliculi run within the plates of hepatocytes, sealed from exposure to the
blood by zonulae occludens between hepatocytes. The network of canaliculi is peripherally connected to the bile ducts running along each vertex of the lobule A network of tiny bile canaliculi run within the plates of hepatocytes, sealed from exposure to the
blood by zonulae occludens between hepatocytes. The network of canaliculi is peripherally connected to the bile ducts running along each vertex of the lobule

Question 9

Describe a portal lobule structure

Answer 9

Portal lobule is defined as the roughly triangular shape drawn between three central veins. This area defines a zone of tissue around a bile duct into which a group of bile canaliculi feed, hence defines a basic “bile secretory” functional unit.

Question 10

Describe an acinar lobule

Answer 10

The “short axis” lies between two portal triads (one edge of the “border” of a classic lobule).The “long axis” lies between two central veins. The acinar lobule defines liver tissue in terms of blood delivery and is divided into 3 different zones.

Question 11

4. Describe the functions of the hepatocyte.

Answer 11

1. Store glucose as glycogen after meal and converts glycogen to glucose while fasting, 2. produce blood proteins such as albumin, fibrinogen and prothrombin, lipoproteins VLDL, LDL, IDL and HDL 3. take up lipid soluble toxins from intestine, bilirubin from spleen and detoxifies them. 4. eliminates excess cholesterol in bile

Question 12

5. Describe the relationship of the hepatocyte to the blood and bile from a structural viewpoint

Answer 12

Hepatocytes are arranged in anatomosing sheets/plates one cell thick, so two sides of the hepatocytes are exposed to blood sinusoids. Bile canaliculi run within the plates of hepatocytes

Question 13

Components of hepatocyte involved in detox

Answer 13

SER (hypertrophies upon exposure to toxins or alcohol), enzymes in SER, enzymes in peroxisomes

Question 14

6. Be able to define the arrangement of the liver sinusoidal endothelial cells and Kupffer cells within the liver.

Answer 14

Between each hepatocyte plate is the sinusoid which contains a fenestrated layer of endothelial cells which allows free passage of all plasma components except RBCs to contact heptaocyte surface. Btw the endothelial cells and hepatocyte is the perisinusoidal space or space of Disse, containing reticular fibers. Kupffer cells (monocyte derivatives) also form part of the fenestrated endothelial layer

Question 15

Function of Kupffer cells

Answer 15

Play a crucial role in defense, as well as in general removal of particulate material from the blood. They phagocytose particulate materials

Question 16

7. Describe the walls of the bile canaliculi, canals of Hering and interlobular bile ducts.

Answer 16

Bile canaliculi form from apposed grooves in adjacent hepatocytes, forming a circumferential belt around each hepatocyte and a network of tubules entirely within hepatocyte plates. Hepatocyte plasma membranes and tight junctions prevent leakage of bile, but near portal triad bile canaliculi lead to bile ductules (Canals of Hering) which lead to interlobular bile ducts of portal triad. These fuse to form lobar ducts which then form common hepatic duct.

Question 17

Epithelial lining of bile ducts

Answer 17

Bile canaliculi walls are composed of adjacent hepatocyte apical plasma membranes. Canals of Hering have cuboidal epithelium with microvillar projections, interlobular bile ducts have initially cuboidal then columnar epithelium as the ducts fuse to form lobar ducts.

Question 18

Components of bile

Answer 18

Cholate derivatives, cholesterol, phospholipids, bilirubin glucuronides, and proteins, electrolytes, IgA

Question 19

What connects the gallbladder to the common hepatic duct

Answer 19

The cystic duct connects gallbladder to the common hepatic duct. These fuse to form common bile duct which joins the pancreatic duct and enters duodenum. The sphincter choledochus/sphincter of boyden is located before the entry of the pancreatic duct and the sphincter of Oddi is located after entry of pancreatic duct

Question 20

8. Be able to describe the mucosa of the gall bladder and explain what it does and what is unique about its structure as compared to other digestive mucosae.

Answer 20

Columnar epithelium has microvilli and tight junctions at apical surface, numerous mitochondria, and folded basolateral surfaces which actively transport salt into basolateral spaces btw cells and water follows where it is taken up by capillaries.

Question 21

describe blood flow through the liver

Answer 21

Deoxygenated blood from portal vein and oxygenated blood from hepatic artery enter liver > interlobar vessels ( one for vein and one for artery) > interlobular vessels (oxygenated and deoxygenated blood mix via capillaries) > perilobular veins and arteries (connect via capillaries) > inlet venules > sinusoids > central vein > sublobar (intercalated) vein > collecting vein > hepatic veins > inferior vena cava

Question 22

3. Explain the relationship between the structure of the sinusoidal surface of the hepatocyte and the blood, and the relevance of this to different hepatocyte functions.

Answer 22

The liver acinus has 3 zones. 1: zone of permanent activity which is first to receive oxygen and nutrients and the first to regenerate in liver disease, b/c it is closest to the sinusoids. 2: zone of varying activity. 3: zone around the central vein, the zone of permanent repose which receives less nutrients and is more prone to damage.

Question 23

where does bile concentration occur

Answer 23

bile ducts reabsorb water and electrolytes to start the process

Question 24

recycling of bile salts

Answer 24

After release into the small intestine and functioning in the emulsification of lipids in the duodenum and jejunum, bile salts are almost entirely reabsorbed in the ileum and the first part of the colon and returned to the liver for reutilization.