Tissue fixation types mechanism( bone, skin, biopsies, liver) histology

It is fixation is important in tissue processing because it preserves the anatomy of different tissues. It makes tissue hard so that a thin section can be made from it.

 

Tissue fixation means the process by which components of the cell and tissues are fixed physically and partially by chemical methods. So that it can bear subsequent treatment with various reagents.

The chemical compound used for fixation is called fixative.

What is the mechanism of tissue fixatives in histology?

Most of the fixatives work by precipitating the tissue protein. After that, it forms meshwork to hold the other cell components.

Note: A good fixative is an important factor for the production of satisfactory results in the histopathology lab.

 Following factors are important in the mechanism

• Proper penetration of fixative in the tissue
• Fresh tissue sample
• A correct choice of fixative

Inadequate penetration of fixative is the major cause of the poor results. When the tissue section thickness is more than 1 cm, then there will be inadequate penetration of fixative.  To overcome this problem, tissue must be 5 microns thick.

How to fix solid organs, brain, Hollow organs, Lungs, Bone, Biopsies?

There are many kinds of organs for fixation in the histology laboratory. Each organ has its own fixing method.

How to Fixing of Solid organs in histology lab?

Solid organs are cut into slices as big as necessary but not more than five millimeters thick.

Human brain fixing technique in histology

We can fix the human brain in two ways. One if we want to fix an uncut brain, pass a tight thread under the vessels at the base of the brain.

The organ is gently lowered into a bucket filled with fixative, and allowed to float with the help of thread.

Hollow organs fixation method

Hollow organs are fixed by means,

• They are opened and filled with fixative.
• These are packed with cotton soaked in the fixative.

How to fix Lungs in formalin?

Human lungs are fixed by injecting the fixative in the bronchi. In this way, fixative reaches all parts. Putting the container at a place higher than the organ can accomplish it. 

Fixative inflates the bronchi under gravity. When lungs have been inflated, put it in the large bucket containing formalin solution,

How to fix bony tissue in histology lab?

Bones has a different fixing technique. In the case of immediate diagnosis, boney tissue is fixed, and later on, it must be de-calcified by the end-point decalcification method.

Nitric acid and hydrochloric acid (HCL) is used for this purpose. However, these are strong inorganic acids and have rapid action. Therefore bone should be placed more than 24 hours to 48 hours.

Note: Bone marrow trephine biopsies are fixed in Corney’s fixative.

How to fix biopsies?

In order to preserve the biopsies tissue, it is better to first place it on the piece of filter paper, than place it in the fixative solution.

What is the importance of Tissue fixation?

Tissue fixative, preserve the tissue anatomy the same as it removes from the body. After fixation and processing, it strains with hematoxylin & eosin, pap stain, or others.  

In this way, histopathologist easily identifies the abnormality in tissue anatomy.