Functional Histology of the Liver

Question 1

What are the general anatomical features of the liver?

Answer 1

• Large, lobulated exocrine and blood-processing gland, with vessels and ducts entering and leaving at the porta.
• Enclosed by a thin Collagen Tissue capsule, mostly covered by mesothelium.
• Collagen tissue of the branching vascular system provides gross support.
• Parenchymal cells in main solid aspect of organ are supported by fine reticular fibres.

Question 2

The internal structure of the liver has evolved around which vessels?

Answer 2

(a) Portal vein bringing food-rich blood from the gut.
(b) Hepatic artery bringing arterial blood.
(c) Hepatic veins taking away processed blood into the vena cava.
(d) Lymphatics taking away some lymph.
(e) Hepatic ducts removing bile to the gallbladder and gut

Question 3

Describe the blood supply to the liver

Answer 3

• Portal vein 75% (rich in nutrients drains gut and absorbed food)
• Hepatic artery 25% (oxygenated blood)

Question 4

Describe the nerve supply to the liver

Answer 4

sympathetic & parasympathetic supply
of perivascular structures, but very little at sinusoidal
level

Question 5

What is a liver lobule?

Answer 5

• First impression of liver microanatomy is of a uniform mass of large glandular cells throughout the liver substance.
• Closer examination shows that the cells are arranged in perforated plates (hepatocytes), one cell wide. Between the plates are sinusoidal blood channels 9-l2 µm wide, lined by endothelial cells.
• Scattered in the glandular mass are blood vessels, alone and accompanied by other vessels.
• The distribution of these vessels defines or marks out the classic hepatic lobules.

Question 6

What are the types of liver vessels?

Answer 6

(a) Central vein / terminal hepatic venule - very thin wall; lies in the centre of a lobule, with sinusoids converging towards and opening into it.
(b) Sublobular/intercalated vein - thicker wall; lies alone at the periphery of the lobule.
(c) Branch of portal vein - again at the periphery of the lobule, but accompanied by one or more small hepatic arteries/arterioles, one or more bile ducts/ductules lined by cuboidal epithelium, and lymphatics.

Question 7

What is the portal triad?

Answer 7

Portal vein, artery, and bile duct constitute a portal triad; the area in which they lie is a portal area.

Question 8

What is hepatic lobular blood flow?

Answer 8

(a) from branches of the portal vein and hepatic artery so mixes; from the periphery towards the centre; (portal triad to central vein)
(b) in the sinusoids, between the cell plates.
(c) Blood collected in central veins goes to sublobular veins, then to collecting veins, and then hepatic veins leaving the liver.

Question 9

What is intralobular bile flow?

Answer 9

from the lobule’s centre towards the peripheral bile ducts, and runs, within any one cell plate, between the liver cells in bile canaliculi.

Question 10

What is Liver acinus?

Answer 10

Rappaport’s liver acinus represent s a functional unit comprising parts of three or so lobules. It tries to explain differences in exposure to the blood supply among various parts of lobules.

Question 11

What is metabolic zonation?

Answer 11

Such differences (liver acinus) are reflected in varied metabolic functional activities and degrees of susceptibility to toxic agents

Question 12

What are the zones of the liver acinus?

Answer 12

The territory of an acinus has, as its axis, one final branch of the portal vein, and is subdivided into: 1 periportal, 2 intermediate (between portal triad and central vein), and 3 perivenous (close to the central vein) zones, with the initial periportal zone being roughly spheroid, and isolated from periportal zones of adjacent acini.

Question 13

What are the functions of each zone?

Answer 13

1. Sampling components of blood and changes composition (e.g. glycogen to glucose if low blood sugar)
2. Enriched blood

Question 14

What cells are important in liver damage?

Answer 14

• Periportal areas have population of undifferentiated stem cells
• Differentiate if there is evidence of liver damage

Question 15

What are Liver sinusoids?

Answer 15

Sinusoids are low pressure vascular channels that receive blood from terminal branches of the hepatic artery and portal vein (portal triad) at the periphery of lobules and deliver it into central veins.

Question 16

What are liver sinusoids lined with?

Answer 16

Are lined by fenestrated endothelial cells, loosely attached, and hold phagocytic Kupffer cells (surveillance, policemen- phagocytose) (larger, stellate, with a pale oval nucleus), demonstrated by the vital intravascular injection of trypan blue or carbon particles, or latex particles for microscopy in vivo.
Fenestrated lining cells are not tightly attached and rest on microvilli of underlying hepatic cells, without a basal lamina intervening.

Question 17

How can plasma pass through liver sinusoids?

Answer 17

Plasma can thus pass through the sieve plate, formed by the lining cells, out into the perisinusoidal space of Disse to interact with the hepatocytes. Some of this fluid may pass to the periphery of the lobule to be collected as lymph.

Question 18

What is Disse’s space?

Answer 18

contains ECM materials, but not a visible basal lamina.
Area between hepatocytes and fenestrated lining
-Plasma passes through into this space then hepatocytes

Question 19

What are stellate cells?

Answer 19

Scarce, fat-storing, stellate cells of Ito lie outside the endothelial cells. They store vitamin A. They respond to a variety of insults by making collagen (when activated) and causing cirrhosis (fibrosis).

Question 20

What does the sinusoidal wall provide for?

Answer 20

(a) blood cleansing, e.g., of gut bacterial toxins; by Kupffer cells
(b) haemopoiesis in the embryo;
(c) bringing plasma into intimate contact with the hepatic cell for its many metabolic functions of storage, transformations, syntheses, regulation of plasma concentrations, detoxifications, the production of bile, and assisting defence by producing acute-phase proteins.

Question 21

What are Hepatocytes?

Answer 21

Hepatocytes are the chief functional cells of the liver and perform an astonishing number of functions. Roughly 80% of the mass of the liver is hepatocytes

Question 22

How are hepatocytes arranged?

Answer 22

In three dimensions, hepatocytes are arranged in plates that anastomose with one another. The cells are polygonal in shape and their sides can be in contact either with sinusoids (sinusoidal face) or neighbouring hepatocytes (lateral faces). A portion of the lateral faces of hepatocytes is modified to form bile canaliculi. Microvilli are present abundantly on the sinusoidal face and project sparsely into bile canaliculi.

Question 23

What shape are hepatocytes?

Answer 23

Hepatocyte nuclei are distinctly round, with one or two prominent nucleoli. A majority of cells have a single nucleus, but binucleate cells are common.

Question 24

What structures are in a hepatocyte cell?

Answer 24

• Spheroid nucleus
• Extensive granular ER (protein synthesis for enzymes and plasma proteins)
• Smooth ER (steroid hormone and cholesterol metabolism, SER carries enzymes for detoxifications)
• Mitochondria
• Actin filaments
• Microvilli
• Bile canaliculus
• Golgi body and lysosomes help bile synthesis
• Peroxisomes carry catalase enzymes
• Glycogen granules
• Fat droplets after meals
• Lipofuscin/ aging pigment

Question 25

What happens when the liver gets inflamed?

Answer 25

-Inflammatory cells circulate in sinusoids
-Kupffer cells activated
-Stellate cells activated and produced collagen
-Fenestrations close up due to collagen deposition
-Sinusoidal pressure increases
-Hepatocytes die or surrounded by fibrous tissue
-Nodule formation
=Cirrhosis and portal hypertension

Question 26

What are the bile pathways?

Answer 26

• System of canaliculi
• Bile ducts
• Cystic duct

Question 27

Describe the system of canaliculi

Answer 27

(seen easily only with EM or special impregnation) between the hepatic cells leads to Canals of Hering/cholangioles, with both hepatocytes and bile duct cells in their walls.
Next come, in the portal areas,Bile ductules with only small, cuboidal cells, firmly held by membrane interdigitations and junctional complexes, and having a few luminal microvilli.

Question 28

Describe bile ducts

Answer 28

Bile ducts’ epithelium changes to columnar mucous cells and, extrahepatically, the ducts acquire smooth muscle as well as Collagen tissue.

Question 29

Describe the cystic duct

Answer 29

Cystic duct allows reflux into the gallbladder, when sphingther of Oddi at the duodenal outlet of the common bile duct is closed.

Question 30

What is a bile duct?

Answer 30

-Bile is produced at side gardens of hepatocytes
0If they communicate, create bile duct (several bile canaliculi)
-Flow in opposite direction to blood
-Bigger bile duct in portal triad

Question 31

What is in the Canal of Hering?

Answer 31

Stem cells

Question 32

Describe the liver lymphatic system

Answer 32

• Lymph is formed by filtration of plasma into the spaces of Disse as blood flows through the sinusoids.
• Then lymph percolates between the space of Disse and portal tracts then lymphatics are formed that run along portal vessels and biliary ducts.
• The exact anatomical correlation between lymphatics and the rest of liver microanatomy is not entirely clear.