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Histology for Beginners

Histology is the study of the microanatomy of cells, tissues, and organs as seen through a microscope. It examines the correlation between structure and function.

The microscopic study of tissues and cells is known as histology. It includes concentrating on their unmistakable minuscule structure that clarifies the practical and clinical significance of sample under study. Histology is a vital part of medicine as it connects biochemistry, physiology and molecular biology to the investigation of ailment. Histology is used to diagnose various diseases and comprehending pathogenesis.

Biopsies or unhealthy tissue samples from the influenced organs are generally handled, recoloured for observation under the microscope. Histology employs both electron microscopy and light microscopy, contingent upon the prerequisites of the sample being pictured.

This field has extraordinarily progressed, as new practices like cloning,molecular genetics and protein sequencing have given more prominent learning and comprehension of the cells and tissues in the human body.

Introduction to Tissues & Cells


Body tissues are accumulations of cells, gathered in the body as indicated by structure and function. Histology categorises human tissues into four particular types:

  • Nervous: Nervous tissue frames the sensory system, and is comprised of specific cells called neurons. Neurons direct nerve signals starting with one then onto the next as electrical driving forces.
  • Muscular: Muscle tissue is comprised of long slim muscle cells called myocytes. They enable muscular contraction.
  • Connective: Connective tissue frames a connective web all through the body. It fills holes and interfaces distinctive organs and body parts, with the goal that the deliberately organised structure of the body can be kept up.
  • Epithelial: Muscle tissue is comprised of long slim muscle cells called myocytes. They enable muscular contraction.


Cells are the modest living units that structure the organs, tissues and structures inside the body. All cells are composed of cytoplasm and are encompassed by a layer, and contain the accompanying structures of organelles:

  • Mitochondria (produce energy in the form of ATP)
  • Nucleus (comprises DNA)
  • Ribosomes (synthesise proteins)
  • Endoplasmic reticulum (synthesises protein and lipids)
  • Lysosomes (contain digestive enzymes)
  • Vesicles (transport materials within the cell)
  • Golgi body (folded membranes that process proteins from the endoplasmic reticulum)
  • Peroxisomes (contain metabolic enzymes)

Ranging from “Sample to Slide”

The tissue sample undergoes an extensive process before the analysis procedure.


To start with, the tissue should be fixed. This generally includes inundation of the sample with a fixative, for example, formalin. After that, the fixed tissue is dried out and mixed with and installed in (paraffin) wax.

Paraffin Embedded Tissue Block and Stained Slide
Paraffin Embedded Tissue Block and Stained Slide

An option in contrast to fixation is freezing the fresh sample before cutting it into segments. This accelerates the diagnosis process since it sidesteps the fixation procedure. However, that comes to the detriment of section quality.

Other Materials

Paraffin wax does not always provide a sufficiently hard matrix for cutting very thin sections (which are especially important for electron microscopy).

Paraffin wax may also be too soft in relation to the tissue, the heat of the melted wax may alter the tissue in undesirable ways, or the dehydrating or clearing chemicals may harm the tissue.

Alternatives to paraffin wax include, epoxy, acrylic, agargelatincelloidin, and other types of waxes.

In electron microscopy epoxy resins are the most commonly employed embedding media, but acrylic resins are also used, particularly where immunohistochemistry is required.

For tissues to be cut in a frozen state, tissues are placed in a water-based embedding medium. Pre-frozen tissues are placed into molds with the liquid embedding material, usually a water-based glycol, OCT, TBS, Cryogel, or resin, which is then frozen to form hardened blocks.


When the wax sets, the sample is cut into segments 3-10 microns with the help of a machine known as a rotary microtome. Each segment is set in warm water to level out and after that gathered up onto a glass slide.


After wax removal and rehydration process, the specimen is stained for any subtleties. Since various materials will recolour distinctive pieces of tissue tests, different arrangements and recoloring strategies are utilized relying upon the tissue and what is being seen inside the tissue.


In the wake of recoloring, the slide is dried out and after that mounted, implying that an unmistakable mountant substance and a glass spreadsheet are set over the sample to seal it. Histology may concentrate on small structures; however, it’s a major ordeal for medication and organic science.

The development of the microscope has provided researchers better approaches for contemplating and considering living organisms, prompting critical headways in medicinal services and our comprehension of the characteristic world.

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