Posts
The liver is both a secretory and an excretory gland. It secretes about 1000 ml to 1500 ml of bile in 24 hours, of which 80 to 90 % is reabsorbed. Normal secretion of bilirubin is about 5 to 16µml / liter. Functionally, the liver has 4 lobes which are subdivided into many lobules and the later are composed of a radial column of hepatic cells arranged around the central vein. Between the columns of liver cells are sinusoid lined in places by Kupffer's cells which are of a polyhedral structure about 30µ in diameter. The sinusoids are drained to a central vein. The sinusoids are supplied by both the portal and hepatic arteries and through them blood enter the central vein. Liver cells are separated from sinusoid by a space contain tissue fluids draining to hepatic lymphatics. Lymph flow through the liver is about 75 ml /minute. Intercellular canaliculi arise between liver cells and radiate outwards from the central axis of lobules, while vascular capillaries at the side of hepatic cells are going inwards and join to the central vein. The bile canaliculi are devoid of endothelial lining and contain numerous mast cells. Bile ductules are surrounded by collagen fibers. The portal tract lies at the periphery of the lobules, and consists of inter lobar branches of the hepatic artery, inter lobar vein, and bile ductules, all being layered with fibrous capsules. Liver cell cytoplasm contains glycogen, fat, and basophilic material. Mitochondria - the site of energy production contain phospholipids, cytochrome oxidase and succinoxidase. Endoplasmic reticulum similar to basophils is the site of detoxification of drugs, conjugation of bilirubin, synthesis of steroids and synthesis of protein. Acid phosphatase is formed in lysosomes. It is the site of deposition of ferritin, lipofuscin, copper and bile pigments. It also contains hydrolytic enzymes. Bile is formed in the vacuoles of hepatic cells. The liver receives blood from two sources - the portal vein (70 %) and the hepatic artery (30 %). The blood from the superior mesenteric vein (60 %) and splenic vein (40 %) are drained to portal vein. Right lobe receives the blood (contain food) from the mesenteric vein while the left lobe receives blood mainly from splenic vein. The left lobe is relatively larger in infants. Cirrhosis by nutritional deficiency is more likely occurred in the left lobe. Blood flow through liver is about 17ml/kg or 1.5 L / minute (Blood flow / minute through the Heart and Liver per 100 gm are about 85 ml and 100 ml respectively). Normal pressure in the portal vein is about 5 mm to 15 mm of Hg, as compared with about 6mm in hepatic vein, thus an adequate flow through sinusoid takes place. The liver is also a reservoir of blood and thus it has a major role in the control of systemic blood pressure (Sympathetic sinusoidal constrictions cause portal hypertension as well as systemic hypertension). Mixing of blood from portal vein and hepatic artery takes place in sinusoids. Oxygen saturation in the portal vein and hepatic artery are about 50% and 95% respectively. Oxygen saturation is less in the center portion of lobules. So, portal obstruction, hepatic artery thrombosis, emphysema, cardiac failure, and severe anemia etc. affect primarily in the center of liver lobules. Derangements of all hepatic functions is not begun simultaneously. It is progressed in a parallel fashion. The liver is always very susceptible to viruses and toxins due to this borderline supply of oxygen to different portion of lobules..
Formation and destruction of RBC.
Secretion and Elimination of bile: Bile is a complex, alkaline, yellowish green fluid formed in vacuoles of liver cells and discharged to bile canaliculi. Chief constituents are water (98%) and solids (2%). Inorganic salts - Chlorides, Carbonates and Phosphates of Sodium, Calcium, and Potassium (NaHCo3). Bile salts - sodium taurocholate, sodium glycocholate. Pigments - bilirubin, biliverdin, Cholesterol, lecithin, fatty acids and mucin. Bile has too many functions. It acts as a lubricant. It promotes peristalsis. It neutralizes the duodenal and gastric acidity. It is involved in the excretion of Zinc, Mercury, Copper, Pigments, Cholesterol, Lecithin, toxins and bacterias. Bile salts aid emulsification, digestion and absorption of fat. 80% of bile salts are reabsorbed to the liver. The normal ratio of bile salts and cholesterol is about 20:1. When the ratio is reduced to 13:1 precipitation will be taken place.
Formation of glycogen, Neoglucogenesis and glycogenolysis.
Formation of plasma albumin, formation of alpha & beta globulin and deamination of amino acids: A normal individual can produce 1 to 16 gm. of albumin daily. (Gama globulins are not synthesized in liver cells but from plasma cells. Its level is increased in chronic liver damage due to RE system activity.),
Haemostasis: Synthesis of heparin (It prevents intravascular clotting) and fibrinogen. Bile salts insufficiency in the intestine due to obstruction in the bile duct can affect the absorption of fat soluble vitamin K. Thus, synthesis of prothrombin in the liver is inhibited. Prothrombin time may be increased > 22 seconds both in biliary tree obstruction and in the hepatic damage.
Metabolism of lipid and cholesterol: About 2000 mg. of cholesterol is synthesized in the liver and about 1000 mg. is excreted through bile daily. Esterification occurs in liver cells. 25% of cholesterol is esterified normally. Total blood cholesterol level will be increased in biliary obstruction. Esterified cholesterol will be lowered in hepatic cellular damage. So, the ratio of total and free cholesterol (non esterified) is lowered.
Absorption of fat-soluble vitamins.
Formation of the phospholipids from phosphoric acid, glycerol, choline etc.
Storage of fat: Normal fat content of liver is less than 5%. Liver can convert the free fatty acids derived from depot fat and food fat into triglycerides (Neoglucogenesis by insulin).
Storage of Copper, Iron, Folic acid, Vitamin B12, A, D.
Synthesis of Urea, Uric acid, Zinc enzymes (Dehydrogenase is essential for alcohol metabolism).
Production of immune bodies.
Detoxification by the process of hydrolysis, oxidation, reduction and conjugation.
Inactivation of hormones (Estrogen, Adrenal corticoids, Testosterone, Thyroxin, ADH, insulin and glucagon): Hormones are conjugated with liver protein & glucuronic acid. It is excreted through bile. If it is impaired hyper hormonal activity will manifest.
Erythropoiesis.
Production of heat.
Enzymatic functions: ALP is found abundantly in the bile canaliculi, small intestinal epithelium, proximal tubules of kidney, osteoblast of bone, placenta, and in the breast during lactation. Alkaline phosphatase is removed from blood by hepatic cells and excreted through bile. Normal serum level in adults is 4 -13 king Armstrong units /100ml and in children is 10 to 20 KA units / 100ml. Its level is primarily elevated due to obstruction in the icteric phase. Acetyl cholinesterase is exclusively produced by liver cells.
The icterus is associated the haemoglobin destruction. Bilirubin is derived from haemoglobin. 1 gm. of RBC yields 35 mg of bilirubin. Normally 6 gm. of haemoglobin per day is broken down from RE cells of various parts especially in bone marrow, spleen and liver. (4 types of pigments are derived from the breakdown of haemoglobin (Bilirubin, Hemosiderin, Haematozoin, and Haematoidin). Bilirubin conjugates with glucuronic acid and becomes soluble. Conjugation is essential for bilirubin excretion. The conjugated bilirubin only can pass through the glomerular membrane and can be identified in urine by color. Hyperbilirubinemia occurs in case of excess of destruction of RBC, liver damage, or obstruction in biliary ducts. Hyperbilirubinemia occurring in hemolytic jaundice is the unconjugated type. Unconjugated bilirubin is fat soluble. Conjugation will be failed also in deficiency of glucoronyl transferase. Sulphonamide can convert conjugate bilirubin to the unconjugated one. Testosterone and steroids can inhibit transfer of pigments across the liver cells. Insoluble and soluble bilirubin are excreted to the intestine and expelled through the feces as stercobilnogen. Soluble bilirubin is reabsorbed partly through the gallbladder and intestinal lining and excreted through urine as urobilinogen.
The urobilinogen in urine will be high in haemolytic and hepatocellular damage (re excretion failure) with an increase in serum bilirubin. The urobilinogen may be absent in urine either due to lack of conjugation in liver, or failure in transportation through the bile canal system.
Liver functions tests.
Various blood tests are valuable to identify symptomless carriers as well as determining the etiology of some form of chronic liver diseases.
Plasma protein
Plasma albumin level is lowered even in mild hepatocellular disease. The normal level of 3.6 gm. to 4.7 gm. /100 ml may fall to 2 gm in severe liver disease. The globulin fraction is elevated > about 2.8 gm / 100 ml.
Alkaline phosphatase
Normal values varies from 45 -115 UL/L.
Aminotransferases
They are present in all cells, but the concentration is greatest in heart, liver and striated muscles. Normal level of both aspartate aminotransferase (SGOT) and alanine aminotransferase (SGPT) are varying 8 U/ L - 48 U/L and 7 U/L - 55 U/L respectively. Alanine aminotransferase (SGPT) is increased in cellular hepatitis specifically.
Cholesterol
Normal level varies 150 mg / dl to 220 mg/dl.
Plasma glucose
Normal level varies between 80 mg / dl to 120 mg / dl.
Bilirubin level
Normal level varies between 0.2 mg to1.2 mg / dl.
Van den Bergh test
Indirect test (adding alcohol) is positive in hemolytic jaundice and hepatic jaundice. Direct test is positive in obstructive jaundice.
Different types of jaundice | |||
Haemolytic | Hepatocellular | Obstructive | |
Onset | Chronic | Slow | Stormy + |
Distribution of pigment | Conjunctiva rarely affected | On skin before conjunctiva affected | On conjunctiva before the skin affected |
Pruritus | Not | May be | Severe + |
Color of stool | Normal | Normal or yellow | Pale + |
Urine | Urobilinogen (colourless) and urobilin present. | Often no bilirubin as unconjugated and not soluble. | bilirubin present +. Urobilinogen and \ urobilin absent. |
Liver | Little or large, but not palpable | Normal / large/small | Large |
Spleen | Palpable | Rarely palpable | rarely palpable |
Anemia | Severe + | Usually not severe | may or may not be present |
Serum alkaline phosphatase | Little increased | Little increased | Increased + |
Albumin / globulin ratio | Normal | Low albumin, raised globulin + | Normal |
Prothrombin time | Normal | Decreased | Normal except in late stage |
Van den Bergh reaction | Normal | Indirect reaction + | Direct reaction + |
Serum bilirubin | High serum bilirubin + | Moderate bilirubin | Steadily rising |
Antibodies are the proteins produced by WBC which can be detected in blood within weeks of infection and remain detectable in blood for long periods. Antibodies tests are serum HAV antibody, serum HB surface antigen antibody, serum HBV envelop antigen antibody, HBV core antigen antibody; HCV core antigen antibody, and HDV antibody. Viral protein tests are HB surface antigen, HB envelope antigen, HBV DNA, and HCV RNA.
Other investigations
Fine needle biopsy of liver. Avoid unnecessary biopsies because of bleeding and secondary acute inflammations.
