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Forum Name: Studying Clinical Sciences

Question: Liver Function

Anonymous - Sat Jan 04, 2003 12:22 pm

I am searching for information for a physiology assignment question on the vital functions of the liver. The part of the question I need information on, involves identifying the loss of which of these liver functions would be fatal (within a few hours or days) and why?:

- Bile secretion,
- Carbohydrate metabolism,
- Lipid metabolism,
- Protein metabolism,
- Processing of drugs and hormones,
- Excretion of Bilirubin,
- Synthesis of bile salts,
- Liver storage,
- Phagacytosis.

Any information or ideas you could provide on this question would be most appreciated.

Thanx GoldX :^)
Dr. Safaa Mahmoud - Tue Jan 07, 2003 6:22 pm

Liver functions:
Protein metabolism: NH3 liberated from protein catabolism is toxic to cells and is transformed into Urea in side the liver cells to be excreted in urine. Live represents the main site for elimination of ammonia. Deamination of amino acids and their conversion into other compounds like carbohydrates or lipids takes place in the liver and to lesser extent in other tissues. liver is the main site of synthesis of plasma proteins( globulin, Albumin, fibrinogen, lipoproteins and other coagulation factors). All non essential amino acids are synthesized in the liver. Defect in liver function leads to increase of amonia level and amonia encephalopathy however, this is feature of late liver disease with liver failure.
Carbohydrate metabolism: liver is the main site for glycogen synthesis and storage. when the level of glucose is elevated glycogenesis takes place. While during fasting glycogenolysis which degrade glycogen provide blood with glucose. Moreover in prolonged starvation liver is the main site for gluconeogenesis. By which amino acids, lipids and other carbohydrates are transformed into glucose. So liver maintains steady state level of glucose important for cell energy and nutrition.
Lipid metabolism: liver is the main site for synthesis of fatty acids from carbohydrate and proteins. It is most active site for B oxidation of fatty acid and formation of acetoacetic acid from acetyl CoA (which is more water soluble) to drive tissues with energy during starvation and or physical exercise. 80% of Cholesterol is converted into bile salts in the liver. Synthesis of phospholipids and lipoprotiens occurs in the liver which are essential components in the cell membrane structure.

Synthesis of bile slats and bile secretion: bile acids are synthesized in the liver from Cholesterol. Bile secreted from the liver is mixture of bile acids 65%, phospholipids 20%, Cholesterol 4%, proteins 5%, billirubin and bile pigments 0. 3%. bile acids are in conjugation with glycine mainly and tuarine (bile salts). 50% of secreted bile is H2o that contains equivalent amounts of Na and K to that in the plasma however, HCO3 is the major anion while in plasma Cl is the main one, so it is isotonic,. Bile acids are important in lipid digestion and absorption. Also all fat soluble vitamins are absorbed by the aid of bile salts. Defect in bile secretion leads to coagulation defect in few days because of lack vitamin K and subsequently deficient coagulation factor synthesis by the liver.
Storage site: liver is the principle storage site for iron, vitamins(A, D and B12). It also synthesize transferrine and transcobalmine which are important in iron and vitamin B12 absorption and transport respectively. Liver synthesises apoferittin protein which form ferittin the storage form of iron in the liver So it protects the body during temporary states of lack of these vitamins. The reserve for vitamin B12 allow the body to stand it is lack in diet up to 4 month..
Billirubin exceretion: Every 120 days RBCs gets more fragile and hemolysed in the reticuloendothelial system(spleen). The heme part is further metabolised to billirubin which is carried by Albumin into the circulation to the liver. Then conjugated with glocuronic acid and to lesser extent with sulphuric acid to be secreted in bile. Most of it is excreted in stool. About 5% is converted in the intestine into urobilinogen that excreted through the kidney. Small amount of the unconjugated billirubin circulate in the blood. With conditions of excess hemolysis the amount of billirubin exceeds the capacity of the liver to get rid of it, billirubin may be elevated however, in obstructive disease in the billiary tract the elevated billirubin is the conjugated one. In liver disease both are elevated. And also this is feature of liver cell failure.
Hormones and drug metabolisms: drugs and hormones are either activated or degraded in the liver to be excreted in bile (degradation through oxidation, hydrolysis, carboxylation,, methylation ). These end products may also conjugated or not to be excreted outside the body either through the bile or into urine. Toxicity and or defective action of such compounds results from impaired liver function.
Phagocytic function: Von Kupffer cells are one of the reticuloendothelial cells that have phagocytic function . it engulf more than 99% of bacteria reaching the live sinusoids from the intestine through portal circulation (filter system).

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