H 4 Functions of the liver

Ms. TRS

H 4.1 Circulation in the LiverBlood is supplied to the liver through the hepatic portal vein and hepatic artery

The hepatic artery supplies oxygenated blood from the heartThe hepatic portal vein supplies deoxygenated blood from the stomach or intestines – contains nutrients

The hepatic vein drains blood from the liver and carries it back to the heart.Several short veins originate within the lobes of the liver as small branches, which unite to form the hepatic veins. These lead directly to the inferior vena cava, draining blood from the liver.

Circulation in the Liver

Tube connecting to bile duct

Bile caniculus

Sinusoid

H 4. 2 The role of liver in regulating levels of nutrients in blood

• Nutrient levels fluctuate in the bloodstream – based on what?

• Excessively high nutrient levels could damage organs, especially the brain.

• The liver regulates blood nutrient levels before blood reaches the rest of the body.

• Glucose and salts affect osmotic concentration of blood ( increased water in blood/hypertonic/harmful to brain cells).

• Excess amino acids and vitamins can be harmful

Storage of nutrients

Levels of nutrients in the body need to be controlled, otherwise they can rise to levels which can become harmful

• excess glucose causes osmotic stress• excess iron can cause iron deposits in tissues

• excess Vitamin D (calciferol) can cause elevated calcium levels, anorexia, nausea and kidney failure

• excess Vitamin A (retinol) can be fatal30 – 90 g of polar bear liver contains enough

Vitamin A to kill a human if eaten in one meal

H 4.3 Role of liver in storage of nutrientsThe hepatocytes of the liver control levels of iron, Vitamin A and Vitamin D by:

• Absorbing and storing each nutrient when it is in excess

• Releasing the nutrient into the blood stream when levels start to drop

Synthesis of important chemicals

important for cell membranes, bile and steroid synthesis

Some cholesterol is absorbed from foodThe majority of the body’s cholesterol is

synthesised by the liver and used in bile

Synthesis of important chemicals continued

hepatocytes produce 90% of plasma proteins• The main plasma proteins are:

albumin – maintains osmotic pressure and carries molecules of low solubility fibrinogen – involved in clotting

globulins – have a wide variety functions including the transport of iron and sex hormones, preventing oxidation and immune responses

• Hepatocytes produce albumin, fibrinogen and most globulins except immunoglobulins

H 4. 5 Role of liver in detoxification

Detoxification:• Responsible for the removal of many

substances toxic to the body.• Examples:– Ethanol– Food preservatives– Pesticides/herbicides

H 4. 6 Erythrocyte and hemoglobin breakdown

• Senescent erythrocytes are removed by phagocytic cells in the spleen, liver and bone marrow, or…

• … they may rupture, releasing haemoglobin into the plasma

• Haemoglobin is removed from the plasma by phagocytic cells in the walls of the sinusoids, called Kupffer cells

In the Kupffer cells…

Haemoglobin

Globins(protein part)

Amino acids

Iron(sent to bone marrow via blood& recycled)

Bile pigments(formed from

porphyrin ring)

Haem groups(prosthetic group)

passed to hepatocytes

Porphyrin ring

Haem group

A healthy liver and liver with cirrhosis

H 4. 7Alcohol and Liver Damage

• The hepatic portal vein brings alcohol to the liver from the stomach. Alcohol is readily absorbed from the gastrointestinal tract; however, alcohol cannot be stored and therefore, the body must oxidize it to get rid of it. Alcohol can only be oxidized in the liver, where enzymes are found to initiate the process.

• Any alcohol not removed from the blood immediately will recirculate into the sinusoids again via the hepatic artery.– Thus, alcohol can have a MAGNIFIED effect on liver tissue

Prolonged abuse of alcohol can lead to following types of liver damage: The liver is a very tough and resilient organ, capable of regenerating itself. Despite this resilience, prolonged alcohol misuse over many years can damage the liver.

Each time the liver filters alcohol, some of the liver cells die. The liver can regenerate new cells. But after heavy drinking, for many years, the liver will lose its ability to regenerate new cells, causing serious damage

Cirrhosis – scar tissue left from hepatocytes, blood vessels, and ducts being destroyed by alcohol.Fat accumulation – damaged areas often build up with fat deposits.Inflammation – swelling of the liver

3 Functions of the Liver

1. Metabolic regulation2. Hematological regulation3. Bile production

Storage Functions of the Liver

• carbohydrates – stored as glycogen in the liver & muscle. If glucose levels drop too far below 90 mg/dl, glycogen is broken down and glucose is released into the bloodstream.

• iron – large quantities of free iron are toxic, so the liver stores excess iron as ferritin.

Storage Functions of the Liver

• fat soluble vitamins – Vitamins A, D, E, and K are stored in the liver. These reserves are called on when the diet contains inadequate amounts of these vitamins.

Recycling RBCs

• 1st liver enzyme--Alcohol Dehydrogenase (ADH)-----> Acetaldehyde

• 2nd liver enzyme--Acetaldehyde Dehydrogenase----> Acetic Acid

• Acetic Acid oxidized by body organs----> CO2 + H2O

Metabolism of Alcohol

Alcoholic fatty liver disease: It is the first stage of alcoholic liver disease. Heavy consumption of alcohol, even for only a few days, can lead to a build-up of fatty acids in the liver. Fatty liver disease rarely causes any symptoms but it is an important warning sign that the current drinking level is harmful to the health. Fatty liver disease is reversible.

After stopping drinking alcohol for two weeks, the liver should return to normal.

Stages in alcoholic liver disease

Alcoholic hepatitis: It is the second more serious stage of alcoholic liver disease. Extended alcohol misuse over many years can cause the tissues of the liver to become inflamed. This is known as alcoholic hepatitis. In some rare cases, alcoholic hepatitis can occur after drinking a large amount of alcohol in a short period of time (binge drinking).

Alcoholic hepatitis is usually reversible by stopping alcohol consumption for several months or years.

Stages in alcoholic liver disease

Cirrhosis: It is the final stage of alcoholic liver disease. Cirrhosis occurs when prolonged inflammation of the liver has caused scarring of the liver and subsequent loss of function. Loss of liver function can result in death.

The damage caused by cirrhosis is not reversible. In mild to moderate cases, stopping drinking alcohol immediately can prevent further damage. Gradual recovery of the liver function can be achieved. In more severe cases, a liver transplant may be required.

Stages in alcoholic liver disease