pathophysiology of jaundice
Jaundice, is characterized by yellow discoloration of the skin, sclera, and mucous membranes, as a result of an increase in bilirubin concentration (hyperbilirubinemia) and subsequent tissue
deposition. .When red blood cells have completed their life span of approx. 120 days, and each red blood cell traverses through the reticuloendothelial system, as its cell membrane ruptures and become fragile and prone to rupture. Cellular contents, including hemoglobin, are subsequently released into the blood.
The hemoglobin is phagocytosed by macrophages , and split into its heme and globin portions.The remainder comes from prematurely destroyed erythroid cells in the bone marrow and form hemoproteins such as myoglobin and cytochrome. Due to imbalance in bilrubin formation and clearance there results in Elevated serum bilirubin occurs. Elimination of bilirubin requires conversion to water-soluble conjugates by the hepatocytes through the action of uridine diphosphate (UDP)-glucuronyl transferase (glucuronidation) and secretion into the bile. Conjugated bilirubin, along with bile salts, is then excreted via the biliary system into the duodenum and deconjugated by bacterial enzymes in the terminal ileum and colon. Approximately 20% of deconjugated bilirubin (urobilinogen) is reabsorbed and re- excreted in bile. Unconjugated bilirubin is mostly bound to albumin and is not filtered by the kidney; conjugated bilirubin, however, may be filtered and reabsorbed in the kidney, with a small fraction excreted in the urine. A significant amount of conjugated bilirubin in the urine suggests cholestasis and hepatobiliary dysfunction. The majority of this bilirubin comes from the breakdown of heme from expired red blood cells.
urobilinogen can take two pathways. It can either be further converted into stercobilinogen, which is then oxidized to stercobilin and passed out in the feces, or it can be reabsorbed by the intestinal cells, transported in the blood to the kidneys, and passed out in the urine as the oxidised product urobilin. Stercobilin and urobilin are the products responsible for the coloration of faeces and urine, respectively.