Liver Phsiology Flashcards
What is the liver supplied by?
Nutrients and oxygen?
By both the Hepatic portal vein and the hepatic arteries
Nutrients — hepatic portal vein
Oxygen - hepatic artery
What des the hepatic portal vein receive blood from?
Superior mesenteric artery and the splenic vein
The superior mesenteric vein carry’s nutrient rich and oxygen poor blood
What makes up the portal triad?
Bile duct
Portal vein
Hepatic artery
What makes up the biliary tree?
Bile is initially secreted from hepatocytes and drains from both lobes of the liver via canaliculi, intralobular ducts and collecting ducts into the left and right hepatic ducts. These ducts amalgamate to form the common hepatic duct.
As the common hepatic duct descends, it is joined by the cystic duct – which allows bile to flow in and out of the gallbladder for storage and release. At this point, the common hepatic duct and cystic duct combine to form the common bile duct.
The common bile duct descends and passes posteriorly to the first part of the duodenum and head of the pancreas. Here, it is joined by the main pancreatic duct which then empties into the duodenum via the major duodenal papilla. This papilla is regulated by a muscular valve, the sphincter of Oddi.
Job of the liver?
Detoxification - filters and cleans blood
Synthesis of clotting factors and carrier proteins e.g albumin
As well as enzymes, glycogen and fats.
Production of bile - hepatocytes
Breakdown of bilirubin - forms after RBCs breakdown in spleen
Regulation of fat metabolism
What is the metabolic roll of the liver?
The liver maintains a continuous supply of energy for the body by controlling the metabolism of CHO and fats
Regulated by endocrine glands - pancreas, adrenal, thyroid etc
Definition of lipids:
They are esters of fatty acids and glycerol or other compounds (cholesterol).
They are insoluble in water
What is a triglyceride?
1 glycerol molecule esterified to 3 fatty acids
Stored in adipocytes and hepatocytes
Difference between saturated and unsaturated fat?
Saturated fat contain all single bonds - they line up and are solids at room temperature
Unsaturated fat have a double carbon bond and pack less tightly and are therefore liquid at room temperature
Lipid function?
Energy reserve
Structural role - cell membrane
Hormone metabolism - cholesterol is the backbone of the sex hormones
Insulin action on the metabolism of lipids:
Insulin increases fat storage in adipocytes
Stimulates lipases breakdown of TG so they can enter and be stored in the adipocytes and reduces export of fatty acids from adipocytes
What are lipoproteins?
They consist of a core containing TGs and cholesterol-esters and a surface monolayer.
Protein to lipid ratio varies
Defined by their density - LDL, HDL, Chlyomicorns
They carry cholesterol and TGs through the circulatory system
What is a chylomicron?
They are a type of lipoprotein that carries lipids from the gut to the muscle and adipose tissue
They are recycled by the liver
How are fatty acids exported from the liver?
TG or cholesterol-ester are synthesised in the SER
They are added to a protein to form a lipoprotein which can migrate the sinusoidal membrane of the hepatocyte and be released
When will fatty acid oxidation increase?
When there is a low glucose concentration in the blood.
Can be mitochondrial beta oxidation
- forms acetyl-CoA subunits regulated by CPT
Peroxisomal beta oxidation
- detoxification of very long fatty acid chains
How do fatty acids regulate gene expression?
They control activity of key transcription factors
Do we need to know about - PPAR?
Why does someone develop a fatty liver?
Increased plasma fatty acids - excess dietary intake
May also have increased FAs released from adipocytes
Decreased FA oxidation
This results in the increased FA uptake from the liver - hepatocytes and hence steatosis of the liver.
50% of diabetic patients
75% of obese patients
What is NAFLD
Non-alcoholic fatty liver disease (NAFLD) is the term for a range of conditions caused by a build-up of fat in the liver.
It develops in 4 stages:
- Simple fatty liver (steatosis) – a largely harmless build-up of fat in the liver cells that may only be diagnosed during tests carried out for another reason
- Non-alcoholic steatohepatitis (NASH) – a more serious form of NAFLD, where the liver has become inflamed; this is estimated to affect up to 5% of the UK population
- Fibrosis – where persistent inflammation causes scar tissue around the liver and nearby blood vessels, but the liver is still able to function normally
- Cirrhosis – the most severe stage, occurring after years of inflammation, where the liver shrinks and becomes scarred and lumpy; this damage is permanent and can lead to liver failure (where your liver stops working properly) and liver cancer
RISK of developing to cirrhosis is much less than the 5% who have steatohepatitis
How to manage NAFLD?
- Lose weight – you should aim for a BMI of 18.5 to 24.9
- Eat a healthy diet – try to have a balanced diet high in fruits, vegetables, protein and carbohydrates, but low in fat, sugar and salt; eating smaller portions of food can help, too
- Exercise regularly – aim to do at least 150 minutes of moderate-intensity activity, such as walking or cycling, a week; all types of exercise can help improve NAFLD, even if you do not lose weight
- Stop smoking – if you smoke, stopping can help reduce your risk of problems such as heart attacks and strokes
