Phosphatidylcholines are structurally important part of the cell membranes. In humans 40–50% of their phospholipids are phosphatidylcholines.Choline phospholipids also form lipid rafts in the cell membranes along with cholesterol. The rafts are centers, for example for receptors and receptor signal transduction enzymes.Phosphatidylcholines are needed for the synthesis of VLDLs: 70–95% of their phospholipids are phosphatidylcholines in humans.Choline is also needed for the synthesis of pulmonary surfactant, which is a mixture consisting mostly of phosphatidylcholines. The surfactant is responsible for lung elasticity, that is for lung tissues ability to contract and expand. For example, deficiency of phosphatidylcholines in the lung tissues has been linked to acute respiratory distress syndrome.Phosphatidylcholines are excreted into bile and work together with bile acid salts as surfactants in it, thus helping with the intestinal absorption of lipids. Acetylcholine synthesis
Choline is needed to produce acetylcholine. This is a neurotransmitter which plays a necessary role in muscle contraction, memory and neural development, for example. Nonetheless, there is little acetylcholine in the human body relative to other forms of choline. Neurons also store choline in the form of phospholipids to their cell membranes for the production of acetylcholine. Source of trimethylglycine
In humans, choline is oxidized irreversibly in liver mitochondria to glycine betaine aldehyde by choline oxidases. This is oxidized by mitochondrial or cytosolic betaine-aldehyde dehydrogenases to trimethylglycine. Trimethylglycine is a necessary osmoregulator. It also works as a substrate for the BHMT-enzyme, which methylates homocysteine to methionine. This is a S-adenosylmethionine (SAM) precursor. SAM is a common reagent in biological methylation reactions.
At birth, infants have relatively high levels of AFP, which fall to normal adult levels by the second year of life. The normal level for AFP in children has been reported as lower than 50 nanograms per milliliter (ng/ml) and 10 ng/ml in adults. An AFP level greater than 500 ng/ml is a significant indicator of hepatoblastoma. AFP is also used as an indicator of treatment success. If treatments are successful in removing the cancer, the AFP level is expected to return to normal. Treatment
Surgical removal of the tumor, neoadjuvant chemotherapy prior to tumor removal, and liver transplantation have been used to treat these cancers. Primary liver transplantation provides high, long term, disease-free survival rate in the range of 80%, in cases of complete tumor removal and adjuvant chemotherapy survival rates approach 100%. The presence of metastases is the strongest predictor of a poor prognosis. References
External links
humpath #2775 (Pathology images)