Lecture: Liver Flashcards
Liver: Gross Anatomy
The Liver is divided into lobes.
“The lobes of the liver are defined surgically by the pattern of blood inflow and the branching pattern of the blood outflow”
Each lobe is supplied by a major division of portal vein & hepatic artery.
Each lobe is drained by a major division of the hepatic vein.
Liver: Microanatomy
Portal triad contains the following:
Dumps into the central vein:
-Portal vein: 75% of blood inflow to liver, already gave up its O2 to the GI tract, this is the second capillary bed
-Hepatic artery: 25% systemic circulation that oxygenates the liver
Goes in the reverse direction:
-Bile ductule: goes out into the bille duct = exocrine outflow
-Lymphatic vessel: liver clears blood of toxin and those waste products that are produced go out with the lymph fluid
“Plates” of hepatocytes separate the inflow circulation from the outflow.
Sinus (sinusoid) capillaries are lined with LSEC and separated from
hepatocytes by the (CT) Space of Disse
Central vein
The beginning of the outflow of the liver. This is where the blood is exposed to the hepatocytes.
Bile canaliculi
Where the bile ductule gets its bile from. Small structures in between hepatocytes
Liver: Embryology
Liver, gall bladder, bile duct and
pancreas derive from endoderm
foregut.
The liver is positioned to receive
blood from the gut.
Liver: Blood Flow
The liver receives a systemic circulation via the hepatic artery (branches off the celiac artery).
The liver receives the majority of its blood from the digestive tract through a venous portal system.
Blood is returned through the hepatic veins, which drain to the inferior vena
cava.
Liver disease may result in portal hypertension, i.e. increased blood pressure in the portal vein. (hypertension because blood is backing up in portal vein)
Portal Hypertension
Blood may try to route itself around the portal circulation if the pressure is too high
Portal hypertension may result in anastomoses at either end of the circulation:
esophageal varices: normal circulation to portal vein may anastomose several places (diagram shows sites of venous drainage of esophagus)
anorectal varices: internal hemorrhoidal veins (dilated venules in region of anal canal) normally drain to superior rectal vein -> portal vein, but abnormally to iliac vein
Functions of the Liver
- bilirubin metabolism
- porphyrin met.
- bile acid met.
- amino acid & protein met.
- carbohydrate met.
- lipid & lipoprotein met.
- hormone met.
- vitamin met.
- trace elements
- detoxification
- ammonia detox.
- bicarbonate neutralization
- alcohol degradation
- reticuloendothelial system
- free radicals & antioxidants
- cellular transport
The Reticuloendothelial System
The space of Disse drains into
portal triad lymphatics (through
the space of Mall).
Reticuloendothelial system - cells
following reticulated endothelia in
lymph nodes, spleen etc.
Mononuclear phagocyte system - macrophages (histiocytes and
resident tissue macrophages)
Space of Disse
space between the sinusoidal endothelium and the hepatocyte
Hard to see, tiny space
A lot of the work done by the hepatocyte takes place here. Hepatocytes can take thing up out of the space or put things in. CT compartment that is basal to the hepatocyte and endothelium
Wispy type 3 collagen
Drains into lymphatic
Space of Disse drains to lymphatics via space of Mall
LSEC
Liver Sinusoidal Endothelial Cell
LSEC …
- are sinusoid, lining sinus capillaries
- endocytose blood waste products. “Some things you don’t need hepatocytes for. These endothelial cells are acting like local macrophages for the blood”
- are self-replenishing
- coordinate liver immune cell population
- secrete hepatocyte growth factor and other cytokines to control liver growth
- are antigen-presenting cells (APCs)
gall bladder
OUTFLOW
stores and concentrates bile diverticulum of common bile duct dorsally directed output
portal vein
INFLOW
blood inflow from gut venous portal system dorsal input
hepatic artery
INFLOW
systemic (oxygenated) blood inflow dorsal input
hepatic vein
OUTFLOW
drains to inferior vena cava ventral output
lymphatics (deep)
OUTFLOW
drain to hilar hepatic nodes dorsal output
bile ductule
delivers bile to duodenum exocrine duct
3 ways that lymph can get out of the liver
1) Through portal triad: lymph drains (through space of Mall) via portal triad lymphatics to hilar nodes & cisterna chyli
2) lymph follows space around central vein & exits with hepatic vein
3) lymph drains to pericapsular regions & exits through capsule adventitial to diaphragm
Cancer metastases tend to follow the path of the lymphatics. This is one of the largest organs that has lymphatic drainage
Hepatocyte
(this one is weird)
The “apical” surface of the hepatocyte faces the bile canaliculus. Bile is the exocrine product.
The “lateral” surface of the hepatocyte faces other hepatocytes, and is separated from the apical surface via tight junctions.
The “basal” surface faces the space of Disse and the sinus (sinusoidal) capillaries.
Hepatocyte microvilli extend from the basal surface into the space of Disse and from the apical surface into the bile canaliculus.
“The functional apical surface contains the bile canaliculi”
Hepatocytes are characterized by glycogen, lipid droplets, RER, free ribosomes and prominent SER, endocytotic vacuoles, numerous mitochondria and a euchromatic nucleus.
Zonation of Hepatocytes
Hepatocytes differ in their particular
combinations of enzymes. Some enzymes are preferentially distributed around the central veins (zone 3, ‘pericentral’), others around the portal triads (zone 1, ‘periportal’), others inbetween (zone 2)
The ‘hepatic acinus’ was defined in an
attempt to emphasize these differences (zones 1,2,3) but in modern literature ‘periportal’ and ‘pericentral’ are more common terms.
Oxygen tension & metabolite concentrations in the blood also change dramatically with these zones.
Ex: Where would a hepatocyte that loves being near oxygen be? Near the portal triad
Where would a hepatocyte that is specialized to break down metabolites? Near the central vein
Kupffer Cells
Look like they are in the sinus, but they have feet sticking into the sinus/space of Disse
Kupffer cells …
- are resident macrophages, seeded during fetal development
-phagocytose blood-borne pathogens
- break down RBCs - hemoglobin into bile pigment
Kupffer cells and other immune cells also show __________
zonation
LSECs secrete cytokines that cause immune cells to localize preferentially to periportal locations
Zonation is dynamic & responds to pathogen load
Hepatic Stellate Cells
also called perisinusoidal cells/Ito cells
Major functions:
-Vitamin A storage
-fibrosis during injury: fibers in liver will be in the CT space of the space of Disse. The more fibrosis there is, the harder it is for the hepatocytes to work by taking things up and out
No need to recognize these cells on a slide
hepatic stellate cells (HSCs also known as perisinusiodal cells, fat-storing cells, or Ito cells) which are important as the cells that produce the collagen in disease states that cause liver fibrosis
canal of Hering
Hepatocyte stem cells reside in the canal of Hering, the connection of the bile ductules with the hepatocyte plates. “connection between bile canaliculi and bile ductule”
Similar in concept to the Space of Mall the connection between the space of Disse and lymphatic drainage
