The structure of the liver The liver is a large, grandular organ weighing approximately 1.5 kg in

the adult. It is composed of the right and left lobe. The left lobe contains two lobes called the quadrate and caudate lobes. The lobes consist of many lobules that perform the functions of the liver. The lobules process many substances in the hepatocytes, parenchymal cells of the liver. The venous blood supply carried by a branch of the portal veins carries highly concentrated foodstuffs, including fats,carbohydrates, and proteins that have ben absorbed from the small intestine. The arterial blood supply provides high concentrations of oxygen for the metabolism of these substances. The lobules are composed of sinusoids, rows of cuboidal hepatocytes , bile capillaries and branches of the hepatic artery and portal vein. The sinusoids and surroundings hepatocytes process the raw materials delivered to the liver from the small intestine.

The sinusoids are lined with cells of the clear phagocyte system, which are called Kupffer cells. The porous endothelial lining allows plasma proteins to pass from the sinusoid to narrow space around the hepatocyte called the space of Disse. This space connects with the lymphatic system and allows drainage of plasma proteins and excess fluid.

Within the liver lobules are canaliculi, which hold the bile procduced by the hepatocytes . a mesh work of bile ducts forms from the canaliculi and terminates eventually in the common bile duct, which empties into the duodenum during digestion. The gallbladder receives bile from the liver and then stores, concentrates, and releases it into the common bile duct under appropriate stimulation.

Front View

Back View

Left lobe

Right lobe

Portal vein

Hepatic Artery

Gall bladder

Inferior vena cava

Left Lateral View

Right Lateral View

Top View

Bottom View

Common hepatic duct

Common bile duct

Cystic duct

BLOOD SUPPLY Blood is supplied to the liver through divisions of the

hepatic artery end portal vein, which pass through the complex sinusoidal network to form venules and veins. An admixture of venous and arterial blood is carried into the sinusoids, which are the capillaries of the liver and provide both oxygen and nutrients to be processed. The venules and veins terminate in the hepatic vein, which empties into the inferior vena cava. The liver requires access to a large quantity of the circulation; about 30 % of the cardiac output flows through the liver each minute, making this organ a large reservoir for blood. Even with its large volume and flow, the pressure in the portal system remains low. The liver can distend and increase its volume by a great margin before portal pressure increases.

  FUNCTION OF THE LIVER The liver performs a wide variety of vital, life sustain

functions. The hepatocyte is responsible for maintaining these functions through its numerous organelles. The liver has over 500 functions

  PROTEIN SYNTHESIS AND METABOLISM The liver is critical in protein metabolism through its

deamination of amino acids, urea formation, and ammonia removal , plasma protein formation, and interconversion among the different amino acids. About 90 % of all the plasma proteins are formed in the liver cells. Maximally the liver can form 15 to 40 g of protein per day. Unlike fats and carbohydrates proteins are not stored, and the size of the amino acid pool is the result of the actual turnover of the body proteins and amino acids from exogenous or dietary sources.

SYNTHESIS OF AMINO ACIDS The liver takes up amino acids from the nutrient- rich portal blood converts them various

proteins. The amino acids are relatively strong acids that rarely accumulate in the bloodstream. Most amino acids are actively transported through the cell membranes and then converted into cellular proteins after an enzymatic reaction. These cellular proteins can be transported out of the cells to the bloodstream. The amount of amino acids in blood remains fairly constant but may vary slightly with diet and the individual person. After the cells have reached their capacity for storing proteins the excess amino acids can be degraded and used as energy or changed into fat or glycogen and stored.

AMINO ACID METABOLISM The liver is the major site of amino acid metabolism and the process called deamination of

amino acids results in the formation of ammonia. Deamination of amino acids is required before they can be used for energy or for conversion to fats or carbohydrates. Large amounts of ammonia are formed from amino acids and also from bacterial action in the large bowel. The ammonia formed in the bowel is transported to the liver in the bloodstream. The liver normally removes 80 % of ammonia as blood passes through the portal system. The liver then converts the ammonia to urea which is much less toxic to the nervous system and is more readily excreted by the kidneys than is ammonia

SYNTHESIS AND METABOLISM OF PLASMA PROTEINS Plasma proteins mainly synthesized in the liver are large molecules that circulate for the

most part in the blood. Albumin the most abundant plasma protein is made in the liver. It serves many function including binding substances such as bilirubin and barbiturates in the plasma. Albumin is the principal protein necessary for maintain colloid osmotic pressure. Also binds hydrogen ions alters serum pH.

When the amino acids in blood are decreased the plasma proteins are split to make new amino acids to maintain equilibrium. Decreased levels of amino acids stimulate the liver to increase it’s production of plasma proteins. The concentrations of plasma proteins normally remains at a constant ration with more albumin in plasma than globulin. The globulins consist of about 15 % plasma protein and are protein group to which antibodies produced by B lymphocytes belong.

The liver also synthesizes most of the plasma proteins necessary to coagulate blood including prothrombin , the liver uses Vitamin K , the absorption of which depends on the production of bile. Fibrinogen is a large molecule protein formed entirely by the liver and is part of the coagulation cascade.

FAT AND LIPID METABOLISM The liver oxidizes fatty acids through beta oxidation in the

mitochondria. This process provides energy for other cells through the formation of acetylcoenzyme A which enters the citric acid cycle and releases large quantities of energy . the liver also forms ketone bodies which provide energy in certain conditions such as diabetes mellitus and starvation.

The liver synthesizes almost all of the fat from carbohydrates and protein. The fats are mostly in the form of triglycerides which consist of three molecules of fatty acid and glycerol. Once formed these are transported to fat cells in the form of very low –density lipoproteins (VLDL). When lipids are released from VLDL, their structure changes and they become low-density lipoproteins (LDL) and returned from the liver. The LDL is the form of all most of the total cholesterol of the form of plasma. Cholesterol, synthesized in the liver, is used to form bile salt which is important in the absorption of fats in the small intestine. Cholesterol is also used to form steroid hormones. Additionally, phospholipids consisting of phosphoric acid and fatty acids are synthesized in the liver. Both cholesterol and phospholipids are used by the body to form cellular structures and membranes. High-density lipoproteins (HDL) are formed by the liver to scavenge excess cholesterol and triglycerides.

CARBOHYDRATE METABOLISM Carbohydrate may be released by the liver in its usable form, glucose,

after it has been stored in the form of glycogen. About 5% to 7% of normal liver weight is stored glycogen. When blood glucose increases above normal, glycogens is stimulated, this promotes the release of glucose level. Glycogenolysis is the breakdown of glycogen into glucose.

PATHOPHYSIOLOGY OF ASCITES The mechanism responsible for the development of ascites are not

completely understood. Portal hypertension and the resulting increase in capillary pressure and obstruction of venous blood flow through the damaged liver are contributing factors. The failure of the liver to metabolize aldosterone increases sodium and water retention by the kidney. Sodium and water retention, increased intravascular fluid volume, and decreased synthesis of albumin by the damage liver all contribute to fluid moving from the vascular system into the peritoneal space. Loss of fluid into the peritoneal space causes further sodium and water retention by the kidney in an effort to maintain the vascular fluid volume, and the process become self-perpetuating.

As a result of liver damage, large amounts of albumin-fluid, 15L or more, may accumulate in the peritoneal cavity as ascites. With the movement of albumin from the serum decreases. This combined with increased portal pressure, results in movement of fluid into the peritoneal cavity.

CLINICAL MANIFESTATION Increased abdominal girth and rapid weight gain are common

presenting symptoms of ascites. The patient maybe short of breath and uncomfortable from the enlarged abdomen, and striae and distended veins maybe visible over the abdominal wall. Fluid and electrolyte imbalances are common.