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Flashcards in Liver Histology and Physiology Deck (15)
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1

How many lobes is the liver divided into?

• 4 different lobes
• Not necessarily functional, but anatomic

2

What important biochemical processes is the liver involved with?

• First to receive blood from digestive systems, so it gets nutrients AND toxins first
• 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
• Involved in urea formation
○ All these things need intimate connection/association with the blood, so the liver is organized accordingly

3

What is the name of the connective tissue capsule surrounding the liver?

• Glisson's capsule

4

What is the Liver lobule?

• The smallest individual functional unit, or the dead end of the hepatic portal vein and hepatic artery
• Either classical lobule, portal lobule or acinar lobule

5

What is the classic liver lobule?

• Hexagonal-shaped structure of anastomosing plates of hepatocytes arranged radially around a central vein
• At the six vertices of the lobule run the interlobular vessels carrying incoming blood from both the hepatic portal vein and the hepatic artery
○ Blood is not yet mixed in these vessels
• Also at each vertex runs a bile duct and a lymphatic space called the space of Mall

6

Does the bile secretion pathway involve the blood supply initially?

• No, bile secretion is separate from the blood supply
• 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

7

Describe how blood ends up washing both surfaces of the plates of hepatocytes

• Think of each hepatocyte having both ends touching plasma
• Interlobular vessels and the bile duct form the portal triad which is surrounded by loose connective tissue stroma (these are at the vertices of the hexagonal structure)
• Branches from interlobular vessels called the distributing or perilobular branches extend peripherally around the edges of the lobules, distributing blood into the sinusoids between the plates of hepatocytes
• Blood percolates through the narrow sinusoids between the plates en route to the central vein
• It flows over both surfaces of the plates which are usually one hepatocyte cell thick, hence two sides of most hepatocytes are exposed to plasma

8

The portal lobule differs from the classic lobule how?

• Classic lobule is a structure organized around the central vein
• Portal lobule is a triangular shape between three central veins (veins being the vertices of the triangle)
• This area is where a group of bile canaliculi feed
• "bile secretory" functional unit

9

How is the acinar lobule different than the other two lobules?


• Classic and portal lobules
• Another structural definition based on function
• Short axis lies between two portal triads
○ Think of it as a horizontal football with the laces touching the bottom vertex of a portal triad
○ The points of the football are between two different central veins
• Funcitonal in terms of blood delivery
• Distributing branches of the interlobular vessels run along the edges of a classic lobule but run along the short axis of the acinar lobule
• Relevant because exposure to toxins leads to degeneration nearest the distributing vessels
○ However, Lack of oxygenation or nutrients affects hepatocytes nearest the central vein

10

What are zones 1,2 and 3 used for?

• These are areas that have different histological evidence of different pathology
• For instance, glycogen tends to accumulate more eficiently in hepatocytes of the central zone of the acinar lobule which is nearest blood supply

11

What do hepatocytes do?

• Each hepatocyte is capable of performing all funcitons, there is no division of labor between cells
• Metabolically very versatile for nutrient uptake and detoxification purposes and bile formation
• Take up glucose and store as glycogen
• Break down glycogen to release glucose during fasting state
• Produce major blood proteins:
○ Albumin, clotting factors like fibrinogen and prothrombin
• Produce lipoproteins - mainly VLDL
• Conjugate and detox lipid-soluble toxins and bilirubin from spleen
• Excess cholesterol put into bile

12

Characterize the endothelial cells in the sinusoids

• Fenestrated. They must be to allow all proteins and lipoproteins and plasma components to push through without losing the RBC themselves
• All this plasma stuff goes into the space between endothelial cells and the hepatocyte - the perisinusoidal space
○ Aka - space of disse
• Certain silver stains will highlight this space by staining the reticular fibers within it

13

What are Kupffer cells?

• They are between the hepatocytes and sinusoids, acting as a monocyte-lineage-derived filter
• Especially for bacteria and carbon compound blobs which are visible microscopically
• Play major role in defense and particulate removal from the blood

14

What is bile?

• Composed primarily of bile salts which are typically cholate derivatives
• Smaller amounts of cholesterol, phospholipids, bilirubin glucouronides and proteins are also present
• Also there are electrolytes
• Polymeric IgA is a major protein in bile that is transcytosed from hepatocytes
• Interestingly, vesicular fusion for all components EXCEPT proteins is thought to be the mechanism for bile stuff getting out into the canaliculi

15

How does the gallbladder concentrate the bile?

• Tight junctions and lots of active salt transport from apical to basolateral side
• Water will follow osmotically