Lesson 78 - Microanatomy of the liver

What is bile composed of?

water, bilirubin, cholesterol, electrolytes, bile salts

What is bilirubin?

intermediate product of erythrocyte-derived heme breakdown

What happens to bilirubin in the liver?

conjugated to make it soluble

What are hepatic sinusoids?

narrow vascular spaces that run parallel to hepatic cords and transport blood from the hepatic arteries and portal veins toward the central vein

What is important about the cells forming the hepatic sinusoids?

they are fenestrated, allowing for molecules to readily cross the endothelium

What are kupffer cells?

resident tissue macrophages of the liver

Where are kupffer cells located?

within the hepatic sinusoids

What is the portal triad?

connective tissue structure within the liver that contains three prominent structures

What is in the portal triad?

bile ductule, hepatic artery, portal vein

What is the space of disse?

narrow space between hepatocytes and the hepatic sinusoidal endothelial cells

What is the largest gland in the body?

liver

What are the lobes of the liver covered by?

serosa and capsule of connective tissue with smooth muscle cells

What extends from the capsule?

connective tissue to form interlobular connective tissue around each liver lobule

Which species have distinct interlobular connective tissue?

pigs

What is the primary cell of the liver parenchyma?

hepatocyte

What type of cell are hepatocytes?

polygonal epithelial cells

What do hepatocytes look like?

abundant eosinophilic granular cytoplasm and large centrally located round nuclei

What organelles are present in hepatocytes?

mitochondria, smooth and rough endoplasmic reticulum, golgi apparatus, inclusions

What inclusions do hepatocytes have?

lipid droplets and lipofuscin pigment

What are the most common cytoplasmic changes in hepatocytes?

intracytoplasmic glycogen and lipid

How are hepatocytes arranged?

radiating cords/hepatic cords

What separate hepatic cords?

sinusoids

What are sinusoids?

blood vessels lined by endothelial cells

What network surrounds the cells and sinusoids for support?

reticular fiber network

How many surfaces do hepatocytes have?

six

How many types of surfaces do hepatocytes have?

3

What are the types of surfaces hepatocytes have?

microvillous, canalicular, contact

What are the microvillous surfaces?

facing the perisinusoidal space/space of disse

What are canalicular surfaces?

border the bile canaliculi

What are contact surfaces?

between adjacent hepatocytes where apposed cell membranes may have desmosomes and junctions

What are ito cells also known as?

stellate cells, fat storing cells, lipocytes

Where do ito cells reside?

space of disse/perisinusoidal space

How are ito cells identified?

large lipid vacuoles

What is the function of ito cells?

uptake, storage, and maintenance of vitamin A, production of extracellular matrix, regulation of sinusoidal blood flow, hepatic tissue repair following injury

What are kupffer cells derived from?

monocytes

What is the function of kupffer cells?

removing aged red blood cells from circulation and phagocytizing bloodborne microbes and endotoxins absorbed from the GI

What are oval cells?

pluripotent stem cells

What is the function of oval cells?

repopulation of hepatocytes and other hepatic cells

What are pit cells?

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

What do cells have on the border facing into a bile canaliculi?

short microvilli

What helps prevent bile from escaping the canaliculi?

cells have tight junctions

What do the bile canaliculi form near the periphery of the lobule?

larger canals called canals of hering

What do the canals of hering empty into?

bile ductules within the portal triad

What are bile ductules lined by?

simple cuboidal epithelium

What do the bile ductules join?

interlobular bile ducts within the portal canals

What do interlobular bile ducts converge to form?

intrahepatic ducts

What do intrahepatic ducts leave the liver as?

hepatic ducts

What are intralobular ducts lined by?

simple cuboidal or columnar epithelium

What are the extrahepatic ducts?

hepatic ducts, cystic ducts, bile ducts, gall bladder

What lines the extrahepatic ducts?

simple columnar epithelium

How does the liver receive blood?

hepatic artery and portal vein

What do portal veins look like on histology?

larger blood-filled spaces with a thin to inapparent vessel wall

What do hepatic arteries look like on histology?

smaller in diameter but have a more well-developed smooth muscle wall

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

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

What supplies most of the blood to the liver?

portal vein

What does the portal circulation drain blood from?

GI tract, gall bladder, spleen, pancreas

What is a major role of the liver in relation to the portal system?

metabolize nutrients and eliminate toxins and microbes brought in portal vein from the GI

What blood mixes in the liver?

highly oxygenated blood from hepatic artery and poorly oxygenated blood from portal vein

What kind of blood do hepatocytes receive?

blood with reduced oxygenation due to mixing

What is the importance of the reduced oxygenation supply to hepatocytes?

some regions may be more susceptible to hypoxia

What are hepatic sinusoids lined by?

endothelial cells and kupffer cells

What separates the sinusoid epithelium and the hepatocytes?

space of disse

What is the function of the hepatocyte microvilli in the perisinusoidal space?

bathed in plasma, allowing a direct exchange of substances between blood and hepatocytes

What is important about the sinusoids of the ruminant liver?

nonporous endothelium

Where does the central vein lie at?

center of the hepatic lobule

What is the structure of a hepatic lobule?

hexagon-like structure

What do the hepatocellular regions include?

portal, midzonal, centrilobular

What is the portal lobule?

functional unit developed to emphasize the exocrine function of the liver; triangular area consisting of parenchyma of three adjacent classic lobules

What is the axis of the portal lobule?

interlobular bule ductule

What are the peripheral angles of the portal lobule?

central veins of three adjacent lobules

What is the hepatic acinus?

functional unit that describes the vascular supply to the parenchyma

What demarcates the hepatic acinus?

roughly diamond shaped area made of parts of two classic lobules supplied by terminal branches of the interlobular portal venule and interlobular hepatic artery

What are the zones within the hepatic acinus?

zone 1-3

What is zone 1 of the hepatic acinus?

nearest the vascular axis where hepatocytes receive an excellent oxygen and nutrient supply and are most metabolically active

What is zone 2 of the hepatic acinus?

zone of intermediate activity

What is zone 3 of the hepatic acinus?

borders the central vein and is least favorably situated in terms of oxygen and nutrient supply

What does the gallbladder mucosa form when contracted?

plicae

What lines the luminal surface of the gallbladder?

tall simple columnar epithelium

What does the epithelium of the gallbladder contain?

microvilli and tight junctions

What do some species like cattle have in the gallbladder mucosa?

goblet cells

What is the propria submucosa composed of in gallbladder?

loose connective tissue with lymphatic tissue and maybe glands

What is the tunica muscularis composed of in gallbladder?

thin bundles of smooth muscle cells supplied by both sympathetic and parasympathetic