HISTOLOGY OF ANIMAL TISSUE WITH STEPS

Histology is the study of the microscopic anatomy of tissues and cells in animals. Animal tissues can be broadly classified into four main types: epithelial tissue, connective tissue, muscular tissue, and nervous tissue. Each type of tissue has a specific structure and function.

Kidney cortex. Medullary rays

·         Epithelial tissue: Epithelial tissue covers the body surface, lines internal organs, and forms glands. It is composed of closely packed cells with the little extracellular matrix. The cells are arranged in one or more layers and are tightly joined by specialized structures called tight junctions. Epithelial tissue is classified based on the shape of the cells and the number of layers. The squamous epithelium has flat cells, the cuboidal epithelium has cube-shaped cells, and the columnar epithelium has elongated cells.

·         Connective tissue: Connective tissue supports and connects different structures in the body. It is composed of cells and an extracellular matrix. The extracellular matrix consists of fibers and ground substances. The fibers include collagen, elastic, and reticular fibers. The ground substance is a gel-like substance that fills the space between cells and fibers. Connective tissue is classified into several types, including loose connective tissue, dense connective tissue, adipose tissue, cartilage, bone, and blood.

·         Muscular tissue: Muscular tissue is responsible for movement in the body. It is composed of cells called muscle fibers that contain specialized contractile proteins. There are three types of muscular tissue: skeletal muscle, smooth muscle, and cardiac muscle. Skeletal muscle is attached to bones and is responsible for voluntary movement. Smooth muscle is found in the walls of internal organs and is responsible for involuntary movement. Cardiac muscle is found in the heart and is responsible for pumping blood.

·         Nervous tissue: Nervous tissue is responsible for communication and control in the body. It is composed of cells called neurons that transmit electrical signals, and glial cells that support and protect the neurons. Neurons have a cell body, dendrites that receive signals, and an axon that transmits signals to other neurons or muscles. Nervous tissue forms the brain, spinal cord, and peripheral nerves.

 In summary, the four main types of animal tissues are epithelial tissue, connective tissue, muscular tissue, and nervous tissue. Each type of tissue has a specific structure and function and is composed of different types of cells and extracellular matrix. Understanding the histology of animal tissues is important for understanding their physiological functions and for diagnosing diseases.

Steps of histology:

The process of histology involves several steps that are necessary to prepare and examine animal tissues under a microscope. The general steps of histology are as follows:

1. Tissue collection
2.  Fixation
3.  Dehydration
4.  Embedding
5.  Sectioning
6.  Staining
7.  Mounting 
8. Examination 

1.    Tissue collection: The first step in histology is to collect the tissue samples to be examined. The tissue can be obtained from biopsy or autopsy specimens, surgical resections, or experimental animals.

2.  Fixation: Once the tissue is collected, it must be fixed to preserve its structure and prevent degradation. Fixation involves treating the tissue with a fixative solution, such as formalin, which crosslinks the proteins and stabilizes the tissue.

3.   Dehydration: After fixation, the tissue is dehydrated by passing it through a series of increasing concentrations of alcohol. This removes the water from the tissue and prepares it for embedding in a solid medium.

4.   Embedding: The dehydrated tissue is embedded in a solid medium, such as paraffin or resin, to provide support and facilitate sectioning. The tissue is placed in a mold with the embedding medium, which is then solidified by heating or cooling.

5.   Sectioning: The embedded tissue is then sliced into thin sections using a microtome, which can cut sections as thin as a few microns. The sections are placed on glass slides and dried.

6.   Staining: The tissue sections are stained to enhance the contrast and highlight specific structures. Hematoxylin and eosin (H&E) is a commonly used staining method that stains nuclei blue-purple and cytoplasm and extracellular matrix pink.

7.   Mounting: After staining, the tissue sections are covered with a cover slip and mounted on a microscope slide. The mounting medium prevents the tissue from drying out and protects the cover slip.

8.   Examination: The prepared tissue sections are then examined under a microscope to observe the cellular and tissue structures. The images obtained can be photographed or digitally captured for further analysis.

Micrograph of squamous cell carcinoma of the head and neck

In summary, the steps of histology involve tissue collection, fixation, dehydration, embedding, sectioning, staining, mounting, and examination. Each step is critical to obtain high-quality tissue sections for microscopic examination.