General Information
By the end of the year, we hope that you have acquired a reasonable working knowledge of:
- how cells associate to perform the functions for which they are specialized, and
- how organized groups of cells (tissues) are arranged to form the organ systems of the body.
While the emphasis in histology is on the structure of cells, tissues and organs, structure has very little meaning without understanding the function, much of which is also presented in the other components of the curriculum. There is an emphasis to teach comparable subjects at about the same time, and we ask that you try and correlate structure and function. Most diseases cause structural abnormalities that result in the problems with which you, as a physician, must contend. One reason for studying histology (the normal structure) is so that you can better understand a pathological (abnormal) change and the consequences of that change.
You will be spending most of your time studying two dimensional sections of three dimensional structures, and will encounter a number of atypical perspectives caused by the plane of section (Imagine that you are sectioning an orange in sagittal, parasagittal, equatorial and diagonal planes. The appearance of the orange sections is quite different depending upon the plane of section--the same variation in appearance occurs in tissue and organs because of the angle of sectioning). Try to find a typical perspective for your introduction to a new tissue or organ (use your atlas as a guide). Then try to imagine what it would look like in three dimensions.
Teaching Materials
You are expected to learn histology by learning the lecture material AND by studying the slides of tissues and organs using virtual microscopy on the Michigan Histology website. The other items of materials, listed below and in the Medical Histology Dropbox, should serve as the sources of information necessary for you to understand the functional significance of the structures that you view in the virtual images. A link to download the SecondLook™ Histology mobile review application will be provided to you during the first introductory lecture.
The use of a textbook or histology atlas is also recommended:
Lectures
All lectures and laboratory introductions are now available as recording. Please, consult your daily calendar for lecture and laboratory introduction hours. The lecture should serve as a study guide and starting point for each topic area. The lecture handouts will be placed in the Michigan Histology Resource Dropbox (the link to the Michigan Histology Dropbox can be found on the top of each subject webpage and access requires your Michigan Kerberos password). It would be very useful to read the relevant text chapter or at least the learning objectives before attending or viewing the lecture. After learning the lecture content, it will be very important to follow up by doing the online laboratory assignments on the Michigan Histology website.
Laboratory
Histology is a basic science course with an integral online laboratory segment that is provided by this open website. This provides you with an opportunity for "active" independent learning. As you progress through the course, we would appreciate your comments regarding things that are unclear, or that are particularly helpful in the lab guide, as we revise it every year. Please email Dr. Hortsch with your questions and comments. It is advisable to use your histology atlas while doing the laboratory exercises. Please note that performing the laboratory exercises on the Michigan Histology website is an essential part of your histology learning process as it expands and applies the facts learned in the histology lectures and provides you with an opportunity to develop analytical and scientific reasoning skills.
Examinations And Grading
You should expect to be asked 8-10 quiz/exam questions per histology session, typically divided equally between the on-line weekly quizzes and the sequence final exams (i.e. ~4 questions per session on the weekly quiz and ~4 questions per session ont the sequence final exam). All of the questions will be multiple choice and may be either text- or image-based ("still" jpegs or moveable virtual slides). The quiz and exam questions will weigh equally. You will NOT have seen most of the images used for the quizzes and examinations. By doing the laboratory exercises, you are expected to have developed the skills of analyzing and interpreting these images.
Problems and Administration
If you have a histology problem, you can email Dr. Hortsch with any histology question.
Introduction to the Lab
Electron Micrographs: These EM micrographs were generated by Dr. Johannes A. G. Rhodin, who also authored "An Atlas of Histology" (Oxford Press, 1974). More detailed comments on electron micrographs appear at the end of the Epithelia section (the first lesson in this laboratory guide).
Copyright Considerations
Remember that most of the material on the Michigan Histology Website and in the Michigan Histology Dropbox is copyrighted, especially the lecture handouts and the images and the text in the supplementary learning resources. The resources in the Michigan Histology Dropbox are intended to be only used by University of Michigan histology students. Please refrain from posting this material on open or for-pay subscription websites like studyblue.com or quizlet.com as this might violate copyright laws.
From the lecture
- Understand the processes of preparing and viewing tissues by light and electron microscopy.
- Understand the physical bases for the appearance of tissues in the light and electron microscopes (e.g. What is basophilia and what causes structures to be basophilic? What creates the contrasting light and dark regions in an electron micrograph?)
From the lab session
- A brief listing of some common stains is present at the end of this section. You should have a general familiarity with H&E (Hematoxylin and Eosin), Masson, PAS, and elastic stains.
- Become familiar with the various ways to access and view images in the Michigan virtual slide collection
General And Connective Tissue Stains
Hematoxylin and Eosin
Hematoxylin is the most commonly used nuclear stain in histology and pathology although, despite its long use and honorable history, the chemistry of the dye is still not fully understood. Essentially, hematoxylin is a basic dye and complexes with nucleic acids (DNA and RNA in the nucleus; RNA in the cytoplasm) or other negatively charged molecules (such as sulfate groups). Structures that bind hematoxylin are therefore termed "basophilic" (base loving).
Eosin is an acidic dye and the basic structures it stains are termed "eosinophilic" or less commonly "acidophilic" (acid loving). It stains membranes and most proteins. Cells that have large quantities of folded membranes stain intensely with eosin, because of basic amino acids in the membranes (e.g. macrophages contain lots of membrane in the form of phagocytic vesicles as well as basic lysosomal enzymes within those vesicles that stain with eosin). Collagen is generally stained some shade of red/orange whereas actin (such as in smooth muscle cells) is a bit more pink. Elastin, when present in relatively large amounts (such in the walls of blood vessels, in elastic cartilage, and in the esophagus and trachea), will appear glassy red.
A note about acids/bases and their charges: It always seems to a point of confusion as to how it is that an acid such as DNA can have a negative charge when we generally think of something that is acidic as being positively charged (i.e. a solution with lots of H+ ions is "acidic"). However, the better way to think of acids is as proton donors --in solution, an acid such as DNA donates H+ protons (which makes the solution acidic). Upon donating protons, the DNA therefore becomes negatively charged and it is in this state that it binds hematoxylin.
Masson Triple Stain (or "Trichrome")
This dye combination stains mucus as well as collagenous and reticular fibers blue (aniline blue) or green (fast green) depending on the mixes of dyes used; muscle red; nuclei red (they are black if preceded by an iron hematoxylin). This is a commonly used connective tissue stain in both histology and pathology. On your slides the stain is designated "Masson" or "Mass"; but the blue or green collagen is the tip-off.
Elastic stains
- Aldehyde fuchsin
- Aldehyde Fuchsin is a deep purple dye. It stains elastic fibers and granules of beta cells in the islets of Langerhans, cartilage matrix, and stored neurosecretory product in the hypophyseal pars nervosa, among other things. In some of your slides, it is the only stain and therefore only elastin is demonstrated. Other times it is combined with Masson's trichrome.
- Weigert's stain
- Uses a different kind of fuchsin (basic fuchsin), but the result is similar: elastic fibers stain a deep purple color.
- Verhoeff/van Gieson elastic tissue stain
- Verhoeff's hematoxylin contains ferric chloride and iodide which causes it to stain elastic fibers deep purple/black. Frequently counterstained van Gieson's solution with which stains collagen red/orange and cytoskeletal elements (such as actin) yellow-brown.
Silver Stains
In this case silver nitrate is reduced to metallic (black) silver. The process of development and fixation is similar to developing a photograph (stains reticular fibers).
Periodic Acid Schiff (PAS)
This is an extremely useful technique for demonstrating glycoproteins, mucins and some proteoglycans -anything that contains a relatively high amount of sugar groups. It involves the generation of dialdehydes from hexoses (present as the carbohydrate portion of the aforementioned compounds. One of its main uses is the demonstration of basement membranes, especially in the kidney, and/or in sections with epithelia atypia, where breech of the basement membrane is suspected in early carcinomas. An excellent example is slide 210 from the kidney where PAS staining demonstrates the basement membranes (pink lines) of the simple cuboidal epithelium lining the tubules and squamous epithelium in the glomeruli (the round tangles of cells).
