Students in anatomy and physiology and introductory biology, as well as some more advanced life science courses, study microscope slides of tissue samples. This can be confusing for several reasons but chief among them has to do with the complexity of living things. Organs are made up of tissues that are often inextricably inter-related; and microscope slides for study are generally made by sectioning samples of organs. The student who sets out to study a particular kind of tissue will find the tissue of interest on the slide but there will also be several other materials present as well.
How is That a Problem?
Well, if -- for example -- the topic is connective tissue in general and cartilage in particular, when the student looks into the microscope she sees several different kinds of tissues in the organ. The problem is that she can't find the cartilage unless she first knows what it looks like.
Here's an example. . .
This photomicrograph is of a slide labeled hyaline cartilage. It is actually a cross section of trachea, an organ. The trachea has several layers of concentrically arranged tissues. Innermost (Ecc) is pseudostratified, ciliated, columnar epithelium. This tissue lines the interior of the trachea. Next (Esc), is a layer of glandular tissue made up of simple columnar cells. The broadest band of tissue is a portion of a cartilage ring and is made of hyaline cartilage (hC).
The outermost layer (fC) is fibrous connective tissue and it has some adipose tissue (A) within it. You can also see a small blood vessel (bv) and these have a simple squamous epithelial wall.
If the assignment were to study hyaline cartilage and there were no other directions but the label on the slide, the student's confusion would be amply justified. If there are microscope slides of organs, and you do not have slides of isolated tissues, it will be necessary to find another resource to help you locate the tissue you want to observe on the slide you do have. Having an histology atlas or textbook alongside your microscope as you work is a good approach to learning the tissues. The illustrations on this website and others on the Internet can also help where students can work with their microscopes at a computer station.
The single image above clearly identifies the hyaline cartilage. Additional references, like those below, can help with a study of epithelial tissues in the same slide.
ciliated pseudostratified columnar epithelium (~1000X)
The cells of this tissue are tapered, with their nuclei toward the thicker end. And, they lie next to one another like bowling pins stacked head-to-tail. The result is what appears to be two levels of nuclei, suggesting a stratified tissue. The cells' cilia extend into the lumen and beat to move mucous (produced by goblet cells and mucous glands) upward, away from the lungs.
Simple columnar epithelium (~400X)
Note the simple columnar epithelium (Esc), found here making the wall of a mucous gland in the tracheal wall. A simple tissue means its cells are in a single layer; columnar says that the cells are column-shaped. These images are all different parts of the same region on the same "hyaline cartilage" slide. Look at earlier images to identify the relative position of the same object at the different magnifications.
Simple columnar epithelium (~1000X)
Here the same piece of mucous gland illustrated above (Esc) is magnified almost 1000 times. The higher magnification better reveals the difference between the pseudostratified, ciliated, columnar epithelium and the simple columnar epithelium.
Low columnar epithelium (~1000X)
These columnar cells are from the same mucous gland. Compare them to those in the previous photograph and you will see they are not as high. Sometimes called low columnar tissue, cells undergo this morphological change when they become less active.