Basic Histology
Ottavia Delamar
For five decades, Junqueira's Basic Histology has been considered the hands-down best overview of human tissue structure and function. Accessible yet comprehensive, this trusted classic provides everything you need to know about cell biology and histology, integrating the material with that of biochemistry, immunology, endocrinology, and physiology. With coverage of all tissues, every organ system, organs, bone and cartilage, blood, skin, and more, Junqueira's is a valuable foundation for subsequent studies in pathology.
Formatted in a way that optimizes the learning process, Junqueira's is filled with clear explanations, art, and micrographs to clarify key concepts. This is an essential resource for students of medicine and other health-related professions, as well as for advanced undergraduate courses in tissue biology.
This site uses cookies, which we use to enable the functions of the site, to tailor marketing to areas that may be more appropriate for you, and to customize, maintain, & improve the site. By continuing to use this site you are agreeing to our use of cookies for these purposes. Find out more in our Privacy Center..
All content on Eyewiki is protected by copyright law and the Terms of Service. This content may not be reproduced, copied, or put into any artificial intelligence program, including large language and generative AI models, without permission from the Academy.
Knowledge of the histology of the eye is important for understanding disease pathophysiology and treatment, as many diseases of the eye are manifestations of pathology within specific histological layers. This article describes the histological classification of the tissues of the eye and its external structures.
The lacrimal apparatus of the eye produces lacrimal tears in order to prevent dehydration of the eye. Dry eye syndrome is the most common eye disease, and if untreated, it can cause corneal ulcerations, scarring, and even perforation. The lacrimal apparatus is composed of four parts:
The cornea is a modified mucous membrane that covers the anterior portion of the eye. Its tissue elements are highly specialized to order to maintain transparency. It is composed of six histologically distinct layers, from superficial to deep:
The ciliary body is a ring of smooth muscle that spans the inner wall of the eye at the level of the lens. It suspends the lens in place via suspensory ligaments and functions primarily to control the shape of the lens and produce aqueous humor.
1. Retinal pigment epithelium (RPE): The RPE consists of cuboidal to columnar epithelial cells that contain an abundance of melanin granules in order to absorb light and reduce random reflections of unabsorbed light.
3. External limiting membrane (ELM): The ELM is not a true membrane, but it is a region of zonulae adherents between the photoreceptor cells and Muller cells. Muller cells provide structural and nutritional support for the retinal neurons.
The optic disc is the site at which the axons from the retinal ganglion cells converge and exit the eye via the optic nerve. The optic disc contains no photoreceptor cells and creates the blind spot of the retina.
The macula is a yellow-pigmented zone lateral to the optic disc, approximately 5.5mm in diameter. The fovea is an approximately 1.5mm area of specialized avascular retina that can be identified as a depression in the retina in cross-section. The foveola is the central floor of the fovea, approximately 0.35mm in diameter, and is the area of retina with the greatest visual acuity. It can be differentiated from the fovea histologically by an absence of ganglion cells and rods. The cones in this area are narrower than in other parts of the retina, allowing for more cones per unit area.
Basic knowledge of tissue preparation, including staining, is important to know when interpreting pathology reports on either in-patient or out-patient biopsies. It is not always the case that the interpreting pathologist has thoroughly analyzed the tissue sample by including appropriate histologic staining, and this deficiency can retard accurate diagnosis.
Four basic types of human tissue can be stained and viewed using various histological techniques. Epithelium, connective tissue, muscle tissue, and nervous tissue have commonalities but look very distinct structurally after staining. Each stain exists to highlight an important feature or component within a tissue type. For example, one of the most common stains, Hematoxylin, is a basic dye that stains proteins a blue color, while Eosin stains proteins a pink color. These two stains are commonly used together to define intracellular organelles and proteins. Because of the variety of the proteins that exist, some stains were created to highlight a particular protein, which this review will discuss in the following sections. The benefit of using a special stain is that it can highlight the specific protein very well. However, because of its specificity, the other structures will not be seen. For this reason, multiple slides will often be created from a given specimen so that multiple stains can be performed to gather the full range of needed information.
Almost all tissue stains are performed on tissue that has been removed from the body. However, in rare instances, very specialize stains called vital stains can work on tissue remaining in the body. These stains are used for the identification of specific types of tissue and identification of abnormal tissue, so a subsequent biopsy can be more accurate in obtaining abnormal tissue.
Before specific staining can occur, tissue samples must undergo preparation through the following stages: Fixation, processing, embedding, sectioning, and sometimes antigen retrieval. In modern histology laboratories, most of these steps are automated.
Fixation: Fixation uses chemicals to preserve the structure of the tissue in its natural form and protects it from degradation by irreversibly cross-linking proteins. Although several specialized fixatives are available, Neutral Buffered Formalin is a common choice for this step. The fixation step is vital to the rest of the histologic staining procedure because by retaining the chemical composition of the tissue, the sample is hardened and makes the sectioning phase easier. Paraffin-formalin is another effective fixative. Its benefit is that it is the fixative of choice for immunostaining; however, it requires preparation at the time of the fixation. Bouin is a fixative used for examining embryo and brain tissue because of its superior preservation of delicate nuclei and glycogen. Its downside is that it does not preserve kidney tissues well and also distorts mitochondrial structure.[1]
Dehydration: The addition of ethanol accomplishes the dehydration of a sample. It removed water from the sample and further hardens the tissue for eventual light microscopy. After ethanol is applied, and following the completion of tissue dehydration, xylene is used to remove the ethanol.[1]
Embedding: Embedding is the process of putting the sample into a paraffin wax or a plastic resin to enhance the process of extracting cellular structures. This step is to be performed with caution if the goal is to perform immunostaining because the paraffin wax will inhibit the penetration of antibodies, and lead to a false result.[1]
Sectioning: Sectioning involves mounting the specimen on a microtome and cutting it into sections. The preferred thickness is 4-5 micrometers so that it can be stained and put on a microscope slide for examination.[1]
Antigen Retrieval: This step is to retrieve antigens that could have been covered in the fixation and embedding stages. If the cross-linking of proteins conceals the antigen sites, there may not be as robust of an immunohistochemical response. Antigen retrieval is achieved through heating and proteolytic methods to break down the cross-links and reveal the epitopes and antigens that were previously covered.[1] Although this step carries the risk of denaturing both the fixative and the antigens themselves, a successful antigen retrieval method can lead to a much more effective immunostaining intensity.
As the name implies, it is two stains done in subsequent steps. The hematoxylin is a basic dye that stains acidic structures. The resulting color is a purple/blue hue, and structures that are targeted with this dye are named Basophilic. Basophilic structures include DNA in cell nuclei, RNA in ribosomes, and the rough endoplasmic reticulum.[1]
Eosin is a counterstain done after hematoxylin and is an acidic dye that targets basic structures. The resulting color is a pink/red hue, and structures that attract eosin are called eosinophilic.[1] The cytoplasm is an example of an eosinophilic structure.
The gram stain is a sequential staining technique invented for differentiating bacterial species. Its major utility lies in determining the causative organism of bacterial infection by staining the cell wall.[2] While not all bacteria have a cell wall and thus cannot be stained with this method, it is still a very useful and commonly performed stain. A bacterial sample can be heat-fixed and undergo gram stain with these four steps: Primary staining with crystal violet, secondary staining with grams iodine, decolorized with alcohol or acetone, and counterstained with safranin. Gram-positive bacteria are those that contain a thick layer of peptidoglycan, making them retain the violet stain and appear purple. Alternatively, the gram-negative bacteria have a thin layer of peptidoglycan and more lipids in the cell wall, so the decolorizing step washes out the violet more, and the sample appears pink.[2]
The Giemsa stain is commonly used in hematology for its superior ability to stain bone marrow, plasma cells, and mast cells. It is also very popular for identifying blood parasites.[3] The Giemsa stain can also help to visualize chromosome abnormalities through "Giemsa-Based Banding," or observing the alternating darker and lighter nucleotide portions on chromosomes during mitosis.[3]
c80f0f1006