Written by Franzgayle T. Husain

The word histology comes from the Greek word “histo,” which means tissue, and “logos,” which means study. Hence, medical histology refers to the study of the structure of tissues. It examines tissues, cells, and organs from a morphological and molecular standpoint.

Before we delve more into histology, let us first understand the concept of cells and tissues.

Cells and Tissue

The human body is consists of trillions of cells that work various functions. It serves as the fundamental unit of life and is essential for the survival of individuals. When a group of cells has the same structure and function, they form tissues.

Tissues play a significant role in various activities of your body. Different types perform distinct functions, including secretion, movement, and strength. Classification of tissue forms four groups– nervous, Muscle, epithelial, and connective tissue. Once they get damaged by different diseases, it will put your life at risk.

Histology is the opposite of gross anatomy because it focuses more on the cellular level. Medical professionals study the role and anatomy of tissues under the microscope. They examine how it interacts with your body systems and how diseases affect them.

History of Histology

The scientist Marie François Xavier Bichat first did the study of tissues. He was the one who used the term tissue in an anatomical sense. He discovered different weaves and textures in the body and named them layers of tissues.

Bichat was able to discover these during his dissection for his anatomical studies. Bichat then created a classification of these issues based on their distinct textures. His workings made him the father of modern histology and descriptive anatomy.

What is histology used for?

All multicellular organisms possess tissues and organ systems. Thus, scientists examine cells to understand concepts and answer questions in many fields.

Medicine

In medicine, it is vital to understand the normal to identify the abnormal. Using histology allows you to detect any abnormalities in your tissues. Whenever there is a disruption of your cells, it affects your body’s activities. This explains why medical professionals conduct histological tests to diagnose certain diseases.

Agriculture

Examining plants in histological viewpoints helps in identifying chemicals present in the soil. These hazardous chemicals can put your plants at risk. But with histology, you can prevent potential dangers from diseases. Additionally, this can aid in deploying the best control methods in the longer term.

Autopsies

Microscopic tissue examination helps in explaining the cause of death of some patients. This is applicable when macroscopic studies fail to provide specific diagnostic pathology. Microanatomy may disclose information about a person’s environment after they die.

How is histology performed?

In every laboratory work, a specific person works on certain procedures. A histotechnologist examines preserved sections and smears of tissues. They stain these samples and place them under a microscope.

Histotechnologists make sure that a tissue section is of good quality. This allows various interpretations of any microscopic cellular changes. They preserve and process the sample’s structures by following these steps:

1. Fixation. Histotechnologists fix the sample as soon as it arrives in the laboratory. They put it in a liquid fixing agent like formalin. The formaldehyde solution penetrates your specimen, resulting in chemical and physical changes. This helps in preserving the tissue and protecting it from the following stages.

After fixation, the histotechnologist will trim and place your sample in labeled cassettes. Generally, this stage is the crucial part of preparing histological sections. Once there is a delay of fixation, your specimen may become damaged.

2.       Dehydration

Melted paraffin wax is hydrophobic. Thus, it is essential to remove the water first from the specimen. To do this, soak your sample in an increased concentration of alcohol solution. In this way, you can avoid distortion of tissue and remove water and formalin.

3.       Clearing

After dehydration, the specimen is immediately transferred to an intermediate solvent like xylene. This type of solvent is soluble in both ethanol and paraffin wax. Using this will remove the amount of fat present, allowing wax infiltration.

In this stage, the solvent xylene replaces the ethanol in the specimen. But the molten paraffin wax will take its place once the tissue becomes embedded.

4.       Infiltration

Now that the tissue has cleared, a histology wax can infiltrate your specimen. Wax, like paraffin, is liquid at 60°C. Thus, you must let it cool to solidify and allow thin sectioning.

5.       Embedding

Embedding happens after infiltration with wax. You must put the tissue in a mold that contains molten wax. Placing resin on it creates a big solid tissue block. This can be clamped into a microtone and sectioned once it has changed.

In embedding, you must ensure that the specimen is in the correct orientation in a mold. Any errors may result in damaged elements during microtomy.

6.       Section-cutting

Histotechnologists can now trim your tissue specimen into thin sections. They can put it in a microscope slide. They use an instrument called microtome to perform section cutting. It must be in thin sections in the form of a ribbon.

Each routine has its required thickness of your tissue. Most specimens for routine hematoxylin and eosin (H&E) are 3-5 μm in thickness. Meanwhile, specimens for amyloid deposits must be at 8-12 μm.

After cutting, you must transfer these sections to a warm water bath to allow them to float on the surface. You can now pick them up and place them under a microscopic slide.

7.       Staining

Most of your cells appear colorless and transparent, so you must stain them to produce contrast. Using histochemical stain provides a more precise visualization of your specimen. It makes the structures and features of your tissues more visible and easier to examine.

How does histology help diagnose an injury or disease?

Understanding the normal anatomy of your tissues is one way of detecting infection. Healthcare providers interpret the changes that arise caused by diseases. Each condition generates distinct changes of characteristics in your tissue structure. Thus, a histological examination can provide information that helps diagnose illness injuries.

Histopathology, a branch of histology, tackles tissues affected by diseases. Damage of cells and inflammation reactions indicates signs of viral infection. Pathologists look for any changes in your cells that might explain your conditions.

Your tissues contain evidence of a pathological process. Interpreting it provides crucial information for your diagnosis and treatment of your disease. Although some changes are vague, there are others that are obvious.

Cancer is a known disease that results from mutations in your cells’ genes. Histopathologists examine your cells from suspicious lumps in your body. They perform a biopsy to provide information about the type of cancer you might have. It is also one way to determine whether your cancer is malignant or benign.

You must remember that histopathology results are only one piece of the puzzle. Pathologists perform laboratory procedures to identify the virus and confirm the diagnosis. These procedures include immunohistochemistry (IHC), serology, and molecular biology.

What is the difference between cytology and histology?

Cytology and histology both study human cells and tissues. But they differ when it comes to the scope of their study. The former focuses on the structure of a single cell or a small group of cells found in body fluids. While the latter investigates the entire section of human tissue.

Cytology or otherwise known as cytopathology, examines your cells for diagnostic purposes. Medical professionals like pathologists observe any abnormalities in your cells. Hence, they use cytology tests to analyze cells for diagnosis. This explains why cytology is used for screening and diagnosing cancer.

Generally, there are two branches of cytology–exfoliative cytology and intervention cytology.

Exfoliative Cytology

Exfoliative cytology is when a pathologist examines cells shed by your body or scraped from the surface of your epithelial tissue. Smears that have been spontaneously shed or manually removed from epithelial and mucous surfaces may contain these exfoliated cells.

These are some exfoliative cytology that deals with manual tissue brushing.

• Gynecological samples
• Gastrointestinal tract samples
• Skin or mucus samples

There are three examples of exfoliative cytology that involve collecting tissues or fluids that your body sheds. These are:

• Respiratory samples
• Urinary samples
• Discharge or secretion samples

Intervention Cytology

Medical professionals intervene with your body to get cells for cytology tests. This means that they will perform procedures that involve piercing your skin to get samples of your cells. Hence why its name is “Intervention Cytology.”

Fine needle aspiration (FNA) is the most used method of intervention cytology. The FNA is helpful for evident lesions. A medical professional injects a needle into the lesion or on the area that draws out a fluid. They may do a fine-needle aspiration in the following parts of your body:

• subcutaneous soft tissue tumors
• thyroid
• lymph nodes,
• salivary glands
• breast.

What is the role of histology in medicine?

Tissues act as building blocks of your body. It forms your organs as it works together. Thus, histology will help you understand and predict the activities of your organs. This is important in the field of medicine, especially for diagnosing diseases. Medical students can also get a better knowledge of cellular biology.

Studying how these cells work provides different insights into the development of complex organs and your organ systems. The information you gain allows you to monitor how your body reacts when certain diseases or treatments affect you.

Diseases occur when there is a rupture of your cells due to infection. Some disorders involving infected connective tissue include lupus and rheumatoid arthritis. They arise when your collagen and elastin become swollen. This then caused harm to the proteins and body parts they connect.

Medical professionals use histology to study the development of these diseases. Observing their progress helps them to identify suitable treatments. This is also one way of comparing the efficacy of different medications and lifestyle choices on your body.

Furthermore, histological studies contribute to the advancement of medical science. Researchers use tissues to test discoveries and verify theories about drug medication. As for medical students, this widens their knowledge of cellular biology and pathology.

Is medical histology hard?

In research conducted by Garcia et al. (2019), they found that undergraduate biology students find it hard to study histology. The nature of the topic and its terminology made it difficult for them to comprehend. But for P. del Rio-Hortega (1933), histology is an exotic meal where you become addicted as you taste it repeatedly.

Medical schools integrate histology into their curriculum to provide information about biological tissues, animal growth, physiology, and tissue diseases. It also continues to deliver different findings in clinical medicine and advanced research.

Unfortunately, medical students find this complex due to insufficient time and attention. Students suggest that teachers should base their teaching on practical tasks. They must also add anatomy subjects and make histology education more engaging.

Learning histology is challenging, but constant reading will make you appreciate it more. One cannot know medicine well if they have no rich perspective on the tissue-level organization.

References

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