Liver Phsiology

Question 1

What is the liver supplied by?

Nutrients and oxygen?

Answer 1

By both the Hepatic portal vein and the hepatic arteries

Nutrients — hepatic portal vein

Oxygen - hepatic artery

Question 2

What des the hepatic portal vein receive blood from?

Answer 2

Superior mesenteric artery and the splenic vein

The superior mesenteric vein carry’s nutrient rich and oxygen poor blood

Question 3

What makes up the portal triad?

Answer 3

Bile duct

Portal vein

Hepatic artery

Question 4

What makes up the biliary tree?

Answer 4

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.

Question 5

Job of the liver?

Answer 5

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

Question 6

What is the metabolic roll of the liver?

Answer 6

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

Question 7

Definition of lipids:

Answer 7

They are esters of fatty acids and glycerol or other compounds (cholesterol).

They are insoluble in water

Question 8

What is a triglyceride?

Answer 8

1 glycerol molecule esterified to 3 fatty acids

Stored in adipocytes and hepatocytes

Question 9

Difference between saturated and unsaturated fat?

Answer 9

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

Question 10

Lipid function?

Answer 10

Energy reserve

Structural role - cell membrane

Hormone metabolism - cholesterol is the backbone of the sex hormones

Question 11

Insulin action on the metabolism of lipids:

Answer 11

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

Question 12

What are lipoproteins?

Answer 12

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

Question 13

What is a chylomicron?

Answer 13

They are a type of lipoprotein that carries lipids from the gut to the muscle and adipose tissue

They are recycled by the liver

Question 14

How are fatty acids exported from the liver?

Answer 14

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

Question 15

When will fatty acid oxidation increase?

Answer 15

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

Question 16

How do fatty acids regulate gene expression?

Answer 16

They control activity of key transcription factors

Do we need to know about - PPAR?

Question 17

Why does someone develop a fatty liver?

Answer 17

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

Question 18

What is NAFLD

Answer 18

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

Question 19

How to manage NAFLD?

Answer 19

• 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