Structure & function of liver Flashcards
Where is the liver located?
Found in theupper right quadrantof the abdomen
Located in the right hypochondriumandepigastrcarea,
extending into the left hypochondrium
● Mostly located underneath the rib cage as it is vulnerable to injury
List the functions of the liver
- processing
- amino acid, carbohydrate, lipid metabolism
- plasma protein and enzyme synthesis (clotting factor production)
- bile production
- detoxification
- storage pf proteins, glycogen, vitamins and metals
- immune functions
What are the 4 main aspects of the liver?
- vasculature
- parenchymal liver cells
- biliary system
- connective tissue matrix
What are the 4 anatomical lobes of the liver?
Right lobeis the largest and theleft lobeis a flattened smaller one.
▪ Separated along the attachment of thefalciform ligament
o Caudate and aquadrate lobeare part of the anatomical right lobe
Describe the portal circulation?
Blood entering the liver through the portal vein has already been
through the gut capillary bed
o Nutrient rich, low pressure blood
o Any increase in resistance in the liver makes it difficult for
blood to flow through, as it is flowing at a low pressure
● Once the vessels enter the liver via the porta hepatis, they enter
the parenchyma (called connecting sinusoids) and then eventually
drain to the hepatic vein
● Portal vein has a wide calibre and thin walls
List the vasculature of the liver
- hepatic artery proper
- hepatic portal vein
- connecting sinusoids
- hepatic vein
Where does the hepatic artery proper stem from?
Branches from thecoeliac trunk
Describe the Hepatic portal vein
Supplies the liver withdeoxygenated blood, carrying nutrients absorbed from the small
intestine.
This is the dominant blood supply to the liver parenchyma, and allows the liver to perform its
gut-related functions, such as detoxification
Describe the connecting sinusoids
The liver tissue is not vascularised with a capillary network as with most other organs, but consists of blood filled sinusoids surrounding the hepatic cells
Describe the Hepatic vein
leaves the liver on the posterior side
o NB: this is not the same as the portal vein
o Venous drainage of the liver is achieved through three hepatic veins, which drain into theinferior
vena cava
What are the portal tracts?
Hepatic artery and portal vein lie in portal tracts along with bile ducts
What is the pota hepatis?
– “gateway to the liver” o 3 main structures enter/leave the liver at this point: ▪ hepatic artery ▪ hepatic portal vein ▪ bile duct o These are known as the portal triad
Describe the microscopic structure of the liver
- arranged in lobules comprised of rows of hepatocytes radiating out from a central point
Describe the hepatic lobules
Each lobule ishexagonal-shaped, and is drained by a venule in its centre, called acentral vein.
o Blood flows out of the sinusoids into the central vein, removing detoxified substances and
metabolic end products.
o The central vein ultimately reunites with the
hepatic vein transporting these substances out of
the liver.
How does bile drain from the lobules?
Bile produced by the hepatocytes drains into tiny canals called bile canaliculi
o These drain into bile ducts located around the
lobule perimeter
Describe the arrangement of hepatocytes?
Lie in plates and cords
o Each hepatocyte is a plate, joins to neighbouring
hepatocytes
What makes sinusoids different from capillaries?
more leaky than capillaries. In the liver, this is achieved by:
● Fenestrations (holes)
● Less well-developed, thinner basement membrane
● This design specifically enhances exchange
Name the parenchymal liver cells
- hepatiocytes
- endothelial cells
- kupffer cells (macrophages)
- perisinusoidal (fat-storing) cells
- liver associated lymphocytes
What connective tissue can be found in the liver?
- liver capsule
- portal tracts
- parenchymal reticulin
Describe the bile canaculi
o Intercellular adaptation
o Run between hepatocyte plates and cords but run in the opposite direction of blood flow
o Drain into portal tracts (portal triads)
o Lots of active transport (high ATPase activity)
What do the bile canaculi lead to?
=> bile ductules => bile ducts
How can vascular and biliary systems be affected by fibrosis?
some of the incoming and outgoing blood vessels join up
● This means that shunts can form within the liver, which has bad consequences
● Some of the incoming blood starts to bypass the liver as a result
● Fibrosis causes reduced function as there is reduced capacity for work
● Vascular resistance increases, causing portal hypertension
where is bile produced?
liver
Where does bile get stored?
gallbladdrr
What is the function of bile?
aids in digestion of fat in duodenum
What does bile help absorb?
fat-soluble vitamins
Name the fat soluble vitamins
- A
- D
- E
- K
What does bile help excrete?
bilirubin
what is bilirubin derived from?
fromhemoglobinbyglucuronidation
What changes occur to bile in the gallbladder?
concentrated to about 5 times—and sometimes as high as 18
times—the strength of the original secretion.
What hormones control the secretion of bile into the duodenum?
cholecystokinin,secretin,gastrin, andsomatostatinand thevagus nerve
Describe the contents of bile
- bile acids & salts
- phospholipids
- cholesterol
- pigments
- water
- electrolyte chemical
- taurocholic acid
What is taurocholic acid?
chemical is released into the bile by the liver. Plays a role in digestion in the small
intestine (involved in the emulsification of fats)
What are bile salts and acids
synthesised from cholesterol or extracted from bloodstream
What is the function of bile acids or salts?
act as detergents to emulsify fat and reduce surface tension on fat droplets to prepare them for action of pancreatic and intestinal lipases
Where do bile salts come from?
only 10% of the daily requirement for bile salts. The remainder thus has to be
reabsorbed and re-circulated.
Describe the chemical nature of bile salts
The salts are large, negatively charged ions that are not readily absorbed by the upper region of the small
intestine; consequently, they remain in the small intestine until most of the fat is digested.
How are bile salts recycled?
the salts and acids are absorbed and passed back into the bloodstream until
they are once again extracted by the liver; this cycle, from the liver to the small intestine and blood and then back to the liver, is calledenterohepatic circulation
Ileum is the main site of bile salt reabsorption
What does bilirubin levels tell you about the liver?
increase in cholestasis
What does alk phos levels tell you about the liver?
increase in cholestasis
What is alk phos?
alkaline phosphatase - enzyme in the cells lining the biliary ducts of the liver
What is GGT?
gamma glutamyl transpeptidase
What does GGT levels tell you about the liver?
Increase in cholestasis or enzyme induction
What does AST/ALT levels tell you about the liver?
increase in hepatocyte damage
What is ALT?
Alanine transaminase
What is AST?
Aspartate transaminase
What is the significance of raise AST?
raised in acute liver damage, but is also present in red blood cells, and
cardiac and skeletal muscle, so is not specific to the liver.
What is the best way of differentiating between ccauses of liver damage?
using AST/ALT ratio
Describe the pattern of LFTs in pre-hepatic jaundice
- increased total bili
- normal conj. bili
- increased unconj. bili
- normal or raised urobilinogen
- normal urine colour
- normal stool colour
- normal alk phos
- normal ALT and AST
Describe the pattern of LFTs in hepatic jaundice
- increased total bili
- increased conj. bili
- increased unconj. bili
- increased urobilinogen
- dark urine colour
- normal stool colour
- increased alk phos
- v. highALT and AST
Describe the pattern of LFTs in post-hepatic jaundice
- v. high total bili
- v. high conj. bili
- normal unconj. bili
- low urobilinogen
- dark urine colour
- pale stool colour
- v. high alk phos
- increased ALT and AST
What is cirrhosis?
Diffuse (throughout the liver) process with fibrosis and nodule formation
How does cirrhosis occur?
chronic inflammation (broadly “hepatitis”) over many years
o Persistence of injury-causing agent
o Causes (fibrous) scarring (fibrosis) and hepatocyte regeneration
▪ regeneration would be a good thing if the underlying architecture was intact, but the
disturbed architecture leads to formation of nodules instead
▪ Nodules squeeze on surroundings (vasculature and bile ducts), causing reduced blood
flow
What are the main causes of cirrhosis?
● Alcohol or alcohol-like 60-70% ● Hepatitis incl. viral B, C (+D) 10% or more ● Biliary disease 5% ● Unknown 10-15% ● Haemochromatosis 5%
What are the causes of hepatitis?
● Alcohol ● Metabolic disease ● Viral infections ● Auto-immune hepatitis ● Many others
What are the features of fatty liver cirrhosis
● small nodules
● yellowy/orange colour
What are the complications of liver cirrhosis?
- portal hypertension
- liver failure
- hepatocellyular (liver) cancer
Describe the cause of portal hypertension
Cirrhosis increases resistance to blood flow through liver thus increasing pressure in the portal
circulation.
What are the consequences of portal hypertension?
▪ Portal-systemic shunts and varices (gastro-oesophageal junction, around rectum and
umbilicus)
>Veins may rupture to give massive hematemesis and precipitate hepatic failure
and encephalopathy
▪ Ascites
▪ Splenomegaly
What proteins are imapired due to liver damage?
● Albumin ● Transport proteins ● Coagulation and fibrinolysis proteins e.g. Factors II, V, VII-XIII ● Complement ● Protease inhibitors
What are the effects of liver failure
● Jaundice
● Coagulation disorders
● Altered intermediary metabolism e.g. impaired synthesis of urea and glycogen
● Altered xenobiotic metabolism e.g. drugs
● Immune, circulatory and endocrine disturbances
● Reduced albumin and other transport proteins (impaired production of secretory proteins)
