LIVER

• The liver is the largest organ in the body -- 1,200 ~ 1,500 g.
  • It comprises about 1/50 of the total adult body weight, and it is relatively larger in infancy, comprising about 1/18 of the birth weight.
• The liver is located in the right upper quadrant of the abdomen, just below the diaphragm. A thick capsule of connective tissue called Glisson's capsule covers the entire surface of the liver.
• The liver has two lobes, the right and the left. The right lobe is about six times the size of the left.

The liver consists of four systems:

1. Hepatocyte ( liver cell) system

2. Biliary tract system

3. Blood circulatory system

   • Dual blood circulatory system:
     The blood in the liver is supplied by two sets of blood circulatory systems:
     • A) Systemic circulation and
     • B) Portal circulation
   • Blood amount: 1,300 cc of blood flow into the liver every minute, it is about 1/4 of the cardiac output.
   • 3/4 of the blood in the liver is supplied by the portal system, and the remaining 1/4 is supplied by hepatic artery from systemic circulation.

4. Reticulo-endothelial system

1. The metabolism and excretion of carbohydrate, protein (including protein components and coagulation factors) , lipids, drugs, and dyes.
2. The metabolism and excretion of bilirubin, bile acids, cholesterol, hormones, and drugs.
3. Storage of glycogen, vitamins, and minerals
4. Synthesis of plasma proteins, such as albumin and globulin, and clotting factors
5. Enzyme activation
6. Blood detoxification and purification

The liver synthesizes and transports bile pigments and bile salts that are needed for fat digestion. Bile is a combination of water, bile acids, bile pigments, cholesterol, bilirubin, phospholipids, potassium, sodium, and chloride. Primary bile acids are produced from cholesterol. When bile acids are converted or "conjugated" in the liver, they become bile salts.

Bilirubin is the main bile pigment that is formed from the breakdown of heme in red blood cells. The broken-down heme travels to the liver, where is it secreted into the bile by the liver. Bilirubin production and excretion follow a specific pathway. When the reticuloendothelial system breaks down old red blood cells, bilirubin is one of the waste products. This "free bilirubin" is a lipid soluble form that must be made water-soluble to be excreted. The conjugation process in the liver converts the bilirubin from a fat-soluble to a water-soluble form. The liver also plays a major role in excreting cholesterol, hormones, and drugs from the body.

The liver plays an important role in metabolizing nutrients such as carbohydrates, proteins, and fats. The liver helps metabolize carbohydrates in three ways:

• Through the process of glycogenesis, glucose, fructose, and galactose are converted to glycogen and stored in the liver.
• Through the process of glycogenolysis, the liver breaks down stored glycogen to maintain blood glucose levels when there is a decrease in carbohydrate intake.
• Through the process of gluconeogenesis, the liver synthesizes glucose from proteins or fats to maintain blood glucose levels.

The liver synthesizes about 50 grams of protein each day, primarily in the form of albumin. Liver cells also chemically convert amino acids to produce ketoacids and ammonia, from which urea is formed and excreted in the urine. Digested fat is converted in the intestine to triglycerides, cholesterol, phospholipids, and lipoproteins. These substances are converted in the liver into glycerol and fatty acids, through a process known as ketogenesis.

Prothrombin and fibrinogen, substances needed to help blood coagulate, are both produced by the liver. The liver also produces the anticoagulant heparin and releases vasopressor substances after hemorrhage.

Liver cells protect the body from toxic injury by detoxifying potentially harmful substances. By making toxic substances more water soluble, they can be excreted from the body in the urine. The liver also has an important role in vitamin storage. High concentrations of riboflavin or Vitamin B1 are found in the liver. 95% of the body's vitamin A stores are concentrated in the liver. The liver also contains small amounts of Vitamin C, most of the body's Vitamin D stores, and Vitamins E and K.

For more information click on the following link:   The Liver and Biliary System.

PANCREAS

For more information click on the following links:

• The Pancreas
• DIABETES PHYSIOLOGY
• Pancreas
• Liver and Pancreas