1/16/2004

Histology Lab Biology 120

Introduction:

Histology is the study of tissues. Tissues are groups of cells that work together to perform a particular function for an animal. We will be looking at a variety of tissues today. The purpose of this lab is to improve your microscope skills and to introduce you to cells and tissues as they can be seen under the light microscope.

The tissues that you will see have been prepared on microscope slides. The process to prepare slides is long and difficult. First a small piece is dissected from an animal. That piece is embedded in paraffin. It is then sectioned on a device called a microtome that slices very thin slices from the block of paraffin embedded tissue. A microtome is similar to a meat slicer at a delicatessen, but it is much more precise.

After the tissue is sliced, the paraffin is removed and stains are applied to the tissue. The stains attach to different parts of the cell. Some stains attach to nuclei, some to cytoplasm. In most common preparations, the nuclei stain blue and the cytoplasm is red. Finally, the tissue slice is mounted on a slide and a mounting medium (a sophisticated glue) is used to attach a coverslip over the tissue. Now, the tissue is ready for viewing.

Guide to our tissue slides

Please look at all slides. You do not have to look at them in order, but you might check them off in your lab manual as you view them. As you view the slides fill in Table 2.1. This will help you to study in the future.

1. Sea star eggs. Look at these to get an idea of what a cell looks like. 2. Epithelial tissues – these will be tough to differentiate – ask your TA for help. a. Simple squamous epithelium – Frog skin b. Simple cuboidal epithelium c. Simple columnar epithelium – Use the rat intestine slides. Check out the “lumen” (inside) of the intestine. The cells covering the interior lining of the small intestine are columnar epithelium. d. Stratified squamous epithelium 3. Connective tissue a. Cartilage – Tough to differentiate – Your instructor and the TA’s spent a long time looking at these slides. i. Hyaline – There are no filaments of collagen in this cartilage ii. Elastic – There are collagen filaments in this cartilage b. Bone – Our slides are pretty good. Please note the structures emphasized in your lab manual c. Adipose Tissue – fat cells – There are not pictures of this in your manual. Note how the cells are large. In life these would be filled with lipid. d. Loose Connective tissue – we don’t have e. Blood – We have blood from Amphiuma – this is an amphibian The blood of Amphiuma looks very different from the pictures in the book. The red cells have nuclei. Only mammals have blood cells without nuclei 4. Muscle Tissues – in all cases, our slides look just like the book a. Smooth Muscle b. Skeletal (Striated) Muscle c. Cardiac Muscle – intercalated discs make this look a little like bamboo. The intercalated discs are hard to see. They are even hard to see in the picture from your manual. 5. Nervous tissues a. Rat medulla – This is a part of the rat brain. Notice the nerve cells imbedded in all of the other cells. b. Cerebellum Golgi – This slide is a slice of brain tissue that has been treated with a specialized stain, the Golgi stain. The Golgi stain impregnates nerve cells with silver salts so that those dendrites are very visible. Camillo Golgi, who invented the stain, won the Nobel Prize for his work on nerve cells. We will place this valuable slide on the computer microscope so that all can see.

Questions in the Lab Manual

Please answer questions on page 28. Your TA can help you with this part. Your TA may want to check what you have filled in.