Cellular pathology TCA Answer 1: Atherosclerosis A) The most effective histological sample for the diagnosis of atherosclerosis would be a biopsy of a blood vessel. This would allow us to see any build up within the blood vessels and see the severity of the disease, to inform a method of treatment. This sample can be stained using Haematoxylin and Eosin stain (H&E stain). This stain will allow us to effectively see all the necessary structures involved in atherosclerosis and allows us to see the individual components clearly. B) A H&E stain is one of the most commonly used stains in histochemistry. It is used so much because of its ability to clearly show contrast between cells and nuclei. There are four main stages in this stain Removal of wax - This step is crucial because if any wax remains on the slide during staining then it will block the stain from reaching that area of tissue, this will cause large unstained areas and can prove very detrimental to the overall stain. This step is achieved by immersing the slide in xylene. Xylene is used because it can quickly and effectively penetrate through the sample and dissolve any of the wax that is there. The wax then mixes with the xylene to create 'waxy' xylene, this then removed by immersing the slide in alcohol. The slide is then rinsed in water to rehydrate, this step is also crucial because it allows aqueous dyes to properly penetrate the cell and fully dye all of the components, leading to an effective stain. Haematoxylin stain - This is a basic dye stain that can come in many various forms based on any additions that have been made pre-stain. The form used in H&E is commonly Mayer's haematoxylin, which comprises of the dye haematin mixed with aluminium 3+ ions in solution. This version of haematoxylin has a lower concentration of the actual haematoxylin within the mixture with a higher amount of the alum (Rastogi et al., 2019). This solution has high affinity towards acidic structures within a cell which are mainly concentrated within the nucleus in the form of RNA, DNA, the nucleolus, and heterochromatin. This means that when Mayer's haematoxylin is added the nucleus of the cell is dyed a dark purple. Ribosomes and the rough endoplasmic reticulum can also end up stained from this step as there is often RNA present. This can be followed by 'blueing' which involves adding a very weak alkaline solution over the slide to darken the colour of the haematoxylin stain to provide a better contrast in the end result. After this has been completed, the stain can be differentiated with a mild acid to remove any excess stain, care must be taken not to over differentiate of the stain will be lighter and will not provide the required contrast (Rolls and Sampias, n.d.). Eosin stain - This is an acidic dye so will stain any cellular components that were left unstained by the haematoxylin. The eosin will