August 15, 2014

Liver - Anatomy, Functions, Diseases & Tests Explained

Why is liver called a Gland?
Gland is a organ which can secrete chemicals or hormones. In this case Liver produces bile, a substance needed to digest fats. Bile’s salts break up fat into smaller pieces so it can be absorbed more easily in the small intestine.
The liver is the largest glandular organ in the body. Liver is the only organ in the body that can regenerate itself in human body.
The liver is located in the upper right-hand portion of the abdominal cavity, beneath the diaphragm, and on top of the stomach, right kidney, and intestines. Shaped like a cone, the liver is a dark reddish-brown organ that weighs about 3 pounds ( or 1.5 kgs average)
The liver consists of four lobes, they are - the left, right, caudate, and quadrate lobes.
i) The left and right lobes are the largest lobes and are separated by the falciform ligament. ii) The right lobe is about 5 to 6 times larger than the tapered left lobe.
iii) The small caudate lobe extends from the posterior side of the right lobe and wraps around the inferior vena cava.
iv) The small quadrate lobe is inferior to the caudate lobe and extends from the posterior side of the right lobe and wraps around the gallbladder.
The liver lobes are made up of thousands of lobules. These lobules are connected to small ducts that connect with larger ducts to ultimately form the hepatic duct.
The liver is an accessory organ within the human digestive system. This means that it assists with the digestive processes, e.g. by supplying substances useful to the digestive process - but that ingested material, does not pass through the liver. Albumin is a major protein which is formed by the liver.
Sources of Blood to Liver:
There are two distinct sources that supply blood to the liver, including the following:
  • Oxygenated blood flows in from the hepatic artery
  • Nutrient-rich blood flows in from the hepatic portal vein: The hepatic portal vein blood to the tissues of the liver where the contents of the blood are divided up into smaller vessels and processed before being passed on to the rest of the body. Blood leaving the tissues of the liver collects into the hepatic veins that lead to the vena cava and return to the heart.

The liver holds about one pint (13 percent) of the body's blood supply at any given moment. The hepatic duct transports the bile produced by the liver cells to the gallbladder and duodenum (the first part of the small intestine).
The main functions of liver as an accessory organ within the human digestive system are:
a) The secretion of bile and bile salts: Liver cells called hepatocytes secrete bile, which is a a yellow/green (though may appear as dark as brown) slightly alkaline liquid.
b) Phagocytosis of bacteria and dead or foreign materials: Within the liver, blood passes through spaces called sinusoids - instead of through capillaries (as elsewhere in the body). A special type of cell called Kupffer's Cells, which are also known as stellate reticuloendothelial cells, are located in the sinusoids and destroy many types of unwanted particles present in the bloodstream through the liver. Kupffer cells are a type of macrophage that capture and break down old, worn out red blood cells passing through the sinusoids.Such particles include:
Antigens, i.e. other substances from outside of the body,
imperfect or no-longer functioning blood cells( damaged leucocytes and erythrocytes).
c) Maintenance of normal blood glucose level: When blood glucose is low the liver breaks stored glycogen down into glucose, for release into the blood stream. The liver converts certain amino acids and lactic acid into glucose. The liver can convert some other sugar molecules (e.g. fructose, galactose) into glucose. When blood glucose is high the liver converts glucose to glycogen and triglycerides (for storage).
d) Fat Metabolism: Break-down of fatty acids - generating adenosine triphosphate (ATP), which is important for the contraction and relaxation of muscles.
Synthesis of lipoproteins, which are important for the movement of fatty acids, cholesterol and triglycerides to and from cells.
Storage of certain triglycerides
Synthesis of cholesterol (as well as using cholesterol to produce bile salts).
e) Protein Metabolism:
Synthesis of all plasma proteins except for -globulins.
Plasma proteins produced in the liver include:
albumin, lipoprotein, transferrin, caeruloplasmin, globulins (but not -globulins), -antitrypsin, -fetoprotein, fibrinogen, prothrombin, Factors V, VII, IX, X and XII, and XII.
De-amination of excess amino acids, i.e. removal of the -NH2 part (called the "amino group") from amino acids, enabling the remaining parts to be re-used, e.g. for conversion to ATP, carbohydrates, or fats.
Conversion of the ammonia (NH3) resulting from the de-amination of excess amino acids, into urea
f) Excretion of bilirubin: Bilirubin is a component of bile, which is produced by the liver. The source of bilirubin is the heam of aged (i.e. no-longer optimally functioning) red blood cells. Bilirubin is the main bile pigment in humans which, when elevated causes the yellow discoloration of the skin called jaundice.
g) Activation of vitamin D: The liver is one of the parts of the body that, together with the skin and the kidneys, participate in forming the active form of vitamin D.
h) Haematopoiesis: Haematopoiesis is the formation of the cellular components of blood. The liver is the main site of embryonic haematopoiesis. However, this function of the liver ceases before birth (bone marrow having been supplementing the haematopoiesis performed by the liver from about 5 months gestation).

Diseases of Liver:
  1. Hemochromatosis is a disease in which too much iron builds up in your Liver .Its a genetical disease of Liver.
  2. Alpha-1 Antitrypsin Deficiency:  Is an inherited disorder that may cause lung disease and liver disease. Its leads to decreased A1AT activity in the blood and lungs, and deposition of excessive abnormal A1AT protein in liver cells.
  3. Jaundice
  4. Alagille Syndrome
  5. Biliary Atresia
  6. Cirrhosis: Cirrhosis of the liver occurs when the organ becomes scarred and hardened so that it cannot function properly. This is most often caused by chronic liver disease brought on by long-term alcohol abuse or hepatitis C infection.
  7. Galactosemia
  8. Gallstones
  9. Gilbert’s Syndrome
  10. Hemochromatosis
  11. Porphyria
  12. Reye’s Syndrome
  13. Sarcoidosis
  14. Tyrosinemia
  15. Viral Hepatitis A, B, C
  16. Wilson Disease

Liver Function Tests:
These tests include prothrombin time (PT/INR), aPTT, albumin, bilirubin (direct and indirect), and others. Liver transaminases (AST or SGOT and ALP or SGPT) are useful biomarkers of liver injury in a patient with some degree of intact liver function.
Liver dialysis—in which a machine performs the detoxification function of the liver- still a new treatment not fully developed yet.

Liver - Anatomy, Functions, Diseases for General Studies & General Knowledge Biology for UPSC IAS, Civil Service exams APPSC TPSC SSC & Bank PO Clerical Exams.
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