D.3: FUNCTIONS OF THE LIVER Digestion review video com/sites/ /stu dent_view0/chapter26/anim ation__organs_of_digestion.h tml

Background info. The liver is divided into two sections known as lobes. The liver works in conjunction with glass bladder, pancreas and intestines to digest, absorb and process food. Main responsibility of the liver: filter blood from the digestive tract before it goes to the rest of the body. The liver detoxifies chemicals and metabolizes drugs. The liver also secretes bile that ends up in the intestines and makes blood clotting proteins. These are only a few of the livers functions.

Blood supply to the liver Described as a duel blood supply because blood arrives to the liver from two sources. Hepatic artery branches form the aorta, bringing oxygen rich blood directly from the heart. Hepatic portal vein brings blood from the stomach and intestines. This blood can be rich in nutrients but low in oxygen. Inside the liver, the vein divides into sinusoids, similar to capillaries but wider and the walls are not continuously lined with cells.

Capillary or Sinusoid? CapillarySinusoid Continuously lined with cells Direct contact between blood and heptatocytes (liver cells)

Inside the liver… Sinusoids allow blood to come in contact with hepatocytes, and proteins (e.g. albumin) to enter and leave the blood. The hepatic artery divides into arterioles, which join with sinusoids, providing a supply of oxygen. Sinusoids merge with venules, leading to the hepatic vein, which carries blood away from the liver.

Processing by the liver The liver regulates the quantity of nutrients circulating in the blood, in particular, glucose. The liver is able to store glucose as glycogen or break glycogen down into glucose. The body is not able to store proteins or amino acids, therefore the liver breaks these compounds down (energy source) and produces nitrogenous waste. Liver also manages lipids circulating in the blood. Lipids arrive in different forms and leave in a variety of forms. E.g. -Chylomicrons (combination of protein & fat) from the intestine are broken down completely. -Very low density lipoproteins (VLDL) are produced by heptatocytes to transport transglycerides to the blood plasma. -Surplus cholesterol is converted into bile salts.

NutrientInformation GlycogenPolysaccharide carbohydrate, level dependent on action of insulin. IronIron removed and stored after breakdown of erythrocytes/haemoglobin Vitamin A (retinol)Necessary for ‘good’ vision. Night blindness is symptom of deficiency Vitamin D (calciferol)Added to milk in some countries – necessary for healthy bones etc.

Erythrocytes (Red blood cells) Typically have a life span of 120 days. This means they are regularly recycled during the course of a persons life. As a erythrocyte ages, the plasma membrane becomes damaged and the cell is recognized by macrophages. The liver breaks down erythrocytes & hemoglobin. Kupffer cells (aka macrophages, in the lining of the sinusoids) engulf swollen RBC. pter21/animation__hemoglobin_breakdown.html

Summary -As RBC age, they swell. They can be absorbed by Kupffer cells in the liver (if they bust, only the hemoglobin is absorbed) -Kupffer cells line the sinusoids -Hemoglobin is split into globin chains and a heme group -Amino acids from globin chains are recycled. -Heme group is brokendown into iron and bilirubin -Kupffer cells release bilirubin into the blood -Iron is bound to tranferrin and stored in either the liver or the spleen, or taken to the bone marrow to synthesise new RBC.

Jaundice CausesConsequences Concentration of bile above 2.5mg dl- 1 in the blood. Result of liver diseases e.g. hepatitus Blockage of bile ducts Common in new born babies Discoloration of skin and eyes (bilirubin deposited in tissues) Infants with high levels of bilirubin for long periods of time can suffer from neurological damage. Kernicterus results in deafness, cerebral palsy. The only way bilirubin can be made soluble is to react it with glucaronic acid and then secreted into passages called canaliculi with water, elecrolytes, biocarbonate, cholesterol, phospholipds and salts. This is called bile. Jaundice is not a disease, it is a symptom. Often treated by exposure to UV or sunlight to breakdown excess bilirubin

Bile salts Produced from surplus cholesterol. Cholesterol is a raw material for synthesizing vitamin D, steroid hormones, production of bile & is a structural component of membranes. Cholesterol is a lipid and as such is regulated by the liver. INSERT DBQ page 682.

Plasma proteins Endoplasmic reticulum and Golgi apparatus in hepatocytes produce 90% of blood plasma proteins e.g. fibrinogen (clotting), albumin (transport) A typical liver cell may have as many as 13 million ribosomes! A typical liver cell 

MoleculeInformation Plasma proteinsAlbumin – regulates osmotic pressure of fluids Fibrinogen – soluble, blood clotting Globulins – blood protein CholesterolEither ingested and absorbed or synthesised by liver Used to produce bile, cell membranes & other uses

MoleculeSource EthanolAlcoholic drinks Food preservativesAdded to food to prevent spoiling PesticidesUsed in food production Herbicides

Alcohol damages the liver Alcohol is absorbed into the blood, taken to the liver by the hepatic portal vein. Hepatocytes remove some of the alcohol but not all – alcohol has a magnified effect on the liver.

Effects of long-term alcohol abuse : 1.Cirrhosis is the scar tissue that accumulates as a result of alcohol damaging hepatocytes, blood vessels and ducts. Areas affected by cirrhosis cannot function. 2.Fat accumulation, fatty tissue will accumulate in areas of the liver which have been damaged. 3.Inflammation swelling of damaged liver tissue, aka alcoholic hepatitis

Erythrocyte will ‘live’ for approx. four months, so every 120 days bone marrow forms new RBC. RBC are anucleate – therefore cannot undergo mitosis Once a RBC has reached the ‘end’ of its life cycle, the cell will rupture. Releasing haemoglobin into the blood stream. Kupffer cells ingest haemoglobin within sinusoids. Ingestion by phagocytosis.

Haemoglobin Pg. 618, fig Four polypeptides (globin) with a haem group at the centre of each globin. Iron atom at the centre of each haem group. Kupffer cells disassemble haemoglobin. 1Globin are hydrolysed into amino acids & released into blood stream ready for protein synthesis 2Iron atom is removed, some iron is stored in the liver, some is sent to the bone marrow 3What remain is called bilirubin, absorbed by hepatocytes becomes bile.