L78: microanatomy of the liver

what is the largest gland in the animal?

liver

what covers the lobes of the liver?

serosa and a capsule of connective tissue with smooth muscle cells

where does the connective tissue from the capsule extend into the liver lobe as?

interlobular connective tissue to surround each individual liver lobule to provide support to vascular and bile ducts

hepatocytes

primary cells of the liver parenchyma

describe hepatocytes

Polygonal epithelial cells with abundant eosinophilic granular cytoplasm and large, centrally located round nuclei

what cellular features are in hepatocytes?

1. mitochondria

2. smooth and rough ER

3. golgi apparatus

4. inclusions

what does the microscopic appearance of the hepatocyte depend on?

nutritional state of the animal

what are most cytoplasmic changes in hepatocytes due to?

intracytoplasmic glycogen and lipid

what are the neon pink spots?

hepatocyte sinusoids

what are the purple spots?

hepatocyte nuclei

what are the white spots?

lipid vacuoles within hepatocytes

how are hepatocytes arranged?

arranged in radiating cords

what are adjacent hepatic cords separated by?

sinusoids

sinusoids

blood vessels lined by endothelial cells that separate adjacent hepatic cords in the liver

what is the arrow pointing to?

sinusoids

what surrounds the hepatocytes and sinusoids?

a fine network of reticular fibers to help keep everything together

how many surfaces are present on the hepatocyte?

six surfaces, three different types

what are the three different types of surfaces present on the hepatocyte?

1. microvillous

2. canalicular

3. intraceullular surface

what is the surface of the hepatocyte that faces the perisinusoidal space?

microvillous surface

what is the surface of the hepatocyte that borders the bile canaliculi?

canalicular surface

what is the surface of the hepatocyte that is between adjacent hepatocytes?

intracellular surface

what type of surface may you find in hepatocytes where apposed cell membranes may have tight junctions and desmosomes?

intercellular surface

what are ito cells also known as?

1. stellate cells

2. fat storing cells

3. lipocytes

where are ito cells located in the liver?

reside in the perisinusoidal region known as “space of disse”

space of disse

narrow region located between the endothelial cells and hepatocytes where ito cells reside

what are ito cells identified by?

their large lipid vacuoles

what are the functions of ito cells?

1. uptake, storage, and maintenance of vitamin A

2. production of extracellular matrix

3. regulation of sinusoidial blood flow

4. hepatic tissue repair after injury

kupffer cells

phagocytes derived from monocytes that are found within the vascular spaced of hepatic sinusoids lining the endothelial surfaces

what are the functions of kupffer cells?

1. remove aged red blood cells from circulation

2. phagocytize adn remove blood borne pathogens absorbed from GI tract

what cells are difficult to identify on histology unless they have phagocytized cytoplasmic material?

kupffer cells

what are the yellow circles indicating?

kupffer cells

what are the blue lines indicating?

sinusoids

oval cells

pluripotent stem cells that differentiate into several cell types

what is the function of oval cells?

replacement of damaged liver cells and regeneration of liver tissue

pit cells

short-lived granular lymphocytes that reside within hepatic sinusoids and contribute to immunity

what are the yellow lines indicating

bile canaliculi

bile canaliculi

tiny canals between apposed hepatocytes

what structure is bile secreted into?

bile canaliculi

why are tight junctions important in regards to bile?

prevents bile from escaping into the narrow intercellular space adjacent to the canaliculus

where is bile produced?

hepatocytes

canaliculi

expanded intercellular spaces bordered by cell membranes with short microvilli projecting into the lumen

canals of hering

larger canals formed when bile canaliculi join near the periphery of the lobule

where do the canals of hering empty into?

bile ductules within the portal triad

what type of cells line bile ductules?

low simple cuboidal epithelium

what do bile ductules join within the portal canals?

interlobular bile ducts

what cells line the interlobular bile ducts?

simple cuboidal or simple columnar epithelium

intrahepatic ducts

are structures formed by the merging of interlobular bile ducts, transporting bile out of the liver through hepatic ducts

what is the flow of bile starting from the hepatocytes?

1. hepatocytes

2. bile canaliculi

3. canals of hering

4. bile ductules

5. interlobular bile duct

6. intrahepatic duct

7. hepatic duct

8. gall bladder

9. bile duct

10. duodenum

what duct drains the gallbladder?

cystic duct

extrahepatic biliary passages

composed of hepatic ducts, cystic ducts, bile duct, and gall bladder

what ducts unite to form the bile duct?

hepatic ducts and cystic ducts

what duct empties into the duodenum?

bile duct

what type of cells line all extrahepatic ducts?

simple columnar epithelium

MCQ: What cell is responsible for removing broken blood cells, and blood-borne microbes from the liver?

kupffer cells

MCQ: What description is accurate concerning the bile canaliculi?

Lumens are entirely sealed by junctional complexes.

what does the liver receive blood from?

hepatic artery and portal vein

what suppplies most of the blood to the liver?

portal vein

where does blood from the hepatic artery and portal vein empty into?

adjacent peri-portal hepatic sinusoids that flows towards the central vein

what does venous blood from the GI tract contain?

digested nutrients, toxins, and microbes

what is the major role of the liver in receiving this portal circulation?

to metabolize nutrients and eliminate toxins/microbes

hepatic artery

delivers highly oxygenated blood to the liver

what is important to understand about the blood in the liver?

receives highly oxygenated blood from the hepatic artery which mixes with poorly oxygenated blood from the portal vein

where are hepatic sinusoids located?

between hepatic laminae

what two types of cells line sinusoids?

1. endothelial cells

2. stellate macrophages (kupffer cells)

what does the microvilli of hepatocytes extending into the perisinusoidal space allow for?

a direct exchange of substances between blood and hepatocytes

what do the sinusoids of the ruminant liver contain?

nonporous endothelium

describe the hepatic lobule

hexagonal structure with a central vein in middle and hepatocytes forming

what are the hepatocullular regions within the classical lobule?

1. portal 

2. midzonal

3. centrilobular

how does bile flow from the hepatocyte?

from central vein to portal triad

how does blood flow into the hepatocyte?

from portal triad to central vein

portal lobule

a functional unit developed to emphasize the exocrine function (bile secretion) of the liver

what is important to understand about the portal lobule?

cannot observe in a microscope

describe the portal lobule

a triangular area consisting of the parenchyma of three adjacent classic lobules

what is the axis of the portal lobule?

interlobular bile ductule and the peripheral angles

hepatic acinus

functional unit that describes the vascular supply to the parenchyma

describe the structure of hepatic acinus

diamond shaped made of 2 hepatic lobules supplied by terminal branches of the interlobular portal venule and interlobular hepatic arteriole

what are the zones of the hepatic acinus?

1. zone 1

2. zone 2

3. zone 3

which zone of the hepatic acinus is nearest to the vascular axis and what does this mean?

1. zone 1

2. excellant oxygen and nutrient supply = most metabolically active

what zone of the hepatic acinus is responsible for the production of proteins?

zone 1

what zone of the hepatic acinus is the zone of intermediate activity?

zone 2

what zone of the hepatic acinus borders the central vein and what does this mean?

1. zone 3

2. least oxygen and nutrient supply 

what zone of the hepatic acinus is more susceptible to ischemic necrosis?

zone 3

what zone of the hepatic acinus is involved with lipid formation and drug detoxification?

zone 3

what does the acinus highlight and what is it useful for?

1. hepatic blood flow and metabolic activity

2. considering liver disease or pathology

where is bile concentrated and stored?

gallbladder

how does the gallbladder mucosa look in its contracted state?

has numerous folds (plicae)

what lines the luminal surface of the gallbladder?

tall simple columnar epithelium

what covers the epithelial surface of the gallbladder?

1. microvilli

2. tight junctions

what species may have goblet cells in the epithelium of their gallbladder?

cattle

what is the propria submucosa composed of in the gallbladder?

loose connective tissue with lymphatic tissue and glands

what is the tunica muscularis composed of in the gallbladder?

thin bundles of smooth muscle cells

what is 1?

epithelium of gallbladder

what is 2?

propria submucosa of gallbladder

what is 3?

tunica muscularis of gallbladder