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The Use Of Formalin-Fixed And Paraffin-Embedded Tissue

Tissue samples of formaldehyde have been used for nearly 120 years. Its application to histology was quickly adopted and started success stories around the world. Even at this point, a 10% formaldehyde concentration is recommended, which corresponds to a final formaldehyde concentration of approx 4%. 

This formalin concentration is still used today. The only modification after its introduction was the use of neutralizing phosphate buffers to dilute the formaldehyde stock solution, thereby reducing the chemical aggressiveness of formalin.

You can get more information about paraffin-embedded tissue via the web.

paraffin-embedded tissue

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Formalin reacts with protein and nucleic acid side groups and causes protein cross-linking and nucleic acid fragmentation. Nucleic acid fragmentation is caused by depurination, whereas protein cross-linking is mediated by reactive NH3 side groups. 

The effect of formalin is further enhanced if the fixation is carried out (1) at a higher temperature, (2) in an unbuffered solution, or (3) for a longer period of time. 

The use of formalin-fixed (and paraffin-embedded) tissue for protein detection or nucleic acid-based methods requires some consideration to avoid misinterpretation of the results. For breaking down protein networks, enzymatic degradation by proteinases such as proteinase K was initially the method of choice.

Since enzyme treatment is often associated with decreased morphological quality, pretreatment of formalin hot cutting by boiling for several minutes in a buffer with or without high pressure is the main approach for antigen recovery at present. 

This heat pretreatment changes the protein's conformation and allows detection of the appropriate immunogenic epitopes, independent of the cross-linked protein.

Understanding Whole Blood, Serum, And Plasma

Most laboratory tests for clinical purposes are performed on a blood sample. Whole blood contains the liquid fraction of the blood (i.e. plasma) as well as cellular elements which, under certain circumstances, cause clotting. This includes red blood cells, white blood cells, and other components.

"Serum" is a liquid created by the formation of a blood clot, as if it had spontaneously touched a surface such as glass or plastic. There are many firms like Geneticist Inc that provide information about blood plasma serum.

 blood plasma serum

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Plasma is a fluid component of blood. It is obtained when a coagulant is added to whole blood and then placed in a centrifuge to separate the cellular material from the lighter fluid layer. Common anticoagulants are EDTA, heparin, and citrate.

When people donate blood for therapeutic purposes, debt collection agencies try to use the blood within one month. Due to the need for sufficient blood supply to meet unexpected needs, some blood inevitably cannot be transfused because it has been stored for too long.

When the blood is collected, it fills a plastic bag filled with a solution of dextrose and citric acid. Dextrose is a nutrient for some cells in the blood, and complexes citric acid or calcium chelate, which prevents blood clots.

A few minutes after collection, blood is centrifuged in packs of red blood cells and citrate plasma for better storage. Red blood cells, plasma, or both can be transfused, depending on the patient's needs.