Function Human chorionic gonadotropin (hCG) is a glycoprotien hormone secreted by the developing placenta shortly after implantation. Measuring hCG levels can be helpful in identifying a normal pregnancy, pathologic pregnancy, and can also be useful following an aborted pregnancy. There is also a benefit in measuring hCG in a variety of cancers including choriocarcinoma and extra-uterine malignancies Smaller amounts of hCG are also produced in the pituitary gland, the liver, and the colon. As previously mentioned, certain malignancies can also produce either hCG or hCG-related hormone. The hormone itself is a glycoprotein composed of two subunits, the alpha and beta subunits. There are multiple forms found in the serum and urine during pregnancy including the intact hormone and each of the free subunits. HCG is primarily catabolized by the liver, although about 20% is excreted in the urine. The beta subunit is degraded in the kidney to make a
Simmons Citrate Reaction It used to differentiate among the Gram-Negative bacilli in the family Enterobacteriaceae. Principle Citrate agar is used to test an organism’s ability to utilize citrate as a source of energy. The medium contains citrate as the sole carbon source and inorganic ammonium salts (NH4H2PO4) as the sole source of nitrogen . Bacteria that can grow on this medium produce an enzyme, citrate-permease , capable of converting citrate to pyruvate . Pyruvate can then enter the organism’s metabolic cycle for the production of energy . Growth is indicative of utilization of citrate, an intermediate metabolite in the Krebs cycle . When the bacteria metabolize citrate , the ammonium salts are broken down to ammonia , which increases alkalinity . The shift in pH turns the bromthymol blue indicator in the medium from green to blue above pH 7.6. Christensen developed an alternative citrate test medium that does not require the organism