Bio 207 Histology Workshop
Goals: --To familiarize you with some of the tissues most susceptible to cancer. --To contrast normal and cancer tissues. --To demonstrate different levels of structure and function in the human body.
Background:
Histology is the study of tissues. Histology is the area of biology that falls between anatomy (the study of organs and organ systems) and cell biology (the study of the cells that make up tissues). The major tissue types are the epithelia--tissues that form the linings and coverings of the body, connective tissues--those that underlie the epithelia and form much of the “substance” of body structures, muscle tissues--those involved in movement or stretching and nervous tissues--those involved in signaling in the nervous system.
Where do histological slides come from? Start with a particular organ--for example, the lung. To prepare a section of lung for histology, lung tissue was preserved in some way and embedded in paraffin or a plastic medium. Then the tissue was cut into very thin sections using a sharp blade (called a microtome). Finally the embedding medium is cleared away and the section is stained, most commonly with hematoxylin and eosin stains. These give a pink color to the cells and stain the nuclei darker than the rest of the cell (often blue or purple).
One of the most difficult aspects of histology is figuring out what you are looking at. What do you see when you look at a section of lung tissue under the microscope? First we need to recall what the lung does and what its role is in the respiratory system. The respiratory system provides oxygen to the body. It does so by conducting oxygen through a series of tubes (from the mouth and nose to the pharynx, trachea and bronchi). The last of these tubes, the bronchi, branch into smaller ducts in the lungs (the bronchioles) ultimately ending in air sacs called alveoli. Thus in a section of lung tissue you will see mostly cells of the alveoli and bronchioles, along with blood vessels (in order for oxygen to go from the lungs to the heart and out to the various parts of the body, the blood vessels must come in close proximity to the lungs).
What does histology have to do with cancer? In cancer cells are growing out of control. They begin to look and act differently from the cells around them. With current technologies, it is not possible to detect cancer cells at the very earliest stages--these cells look the same as normal cells! Removing tissue samples from a patient, preparing histological sections and observing abnormal cells is how most cancers are currently diagnosed. Most cancers affect epithelial tissues and are often designated as carcinomas. Cancers of the connective tissues and muscle are more rare and are usually referred to as sarcomas. Although blood is considered to be a type of connective tissue, since it must be constantly replenished, it contains many rapidly dividing cells that can become cancerous. Cancers of the circulating blood cells are called leukemias, while solid tumors of blood cells lodged in particular organs are called lymphomas. You will see
1 today to how some of these different cancers affect the structure and appearance of tissues.
Workshop procedure:
Part 1 Lung Cancer: An example to contrast normal vs. cancer tissue
1. We will first briefly run through how to use the microscope, focusing on a slide of human lung.
2. Look at the lung tissue in the slide and compare to the picture of lung cancer on the overhead or on the demonstration slide. What are the differences?
Part 2 Histology of epithelial tissues
Once you are familiar with the microscopes, use them to identify the major types of epithelia. Epithelia are among the tissues most prone to cancer and are also the most easily identified of the different tissue types. Identify the major types of epithelia, esp. simple squamous, simple cuboidal and simple columnar, on the various slides using the following handout as a guide.
Slides to look at Epithelial type
1. lung (alveolar cells and simple squamous endothelial cells of a capillary)
2. kidney (ductal cells) simple cuboidal
3. intestine (cells of intestinal simple columnar lining)
Part 3 Compare normal and cancer tissues
1. Each pair of students will be given two slides, one of a normal tissue section and one of the corresponding tissue affected by cancer. Try to get your slide in focus, look at it briefly, then look at that of your partner. You may want to stay with lower power objectives at first to try to scan around and figure out what you’re looking at. If you are assigned a slide of a leukemia or lymphoma, first get your slide in focus under the 40x objective (400x magnification) and then ask the instructor to help you add immersion oil and switch to the oil immersion lens (100x objective) for optimal viewing.
2. Begin to figure out what you are looking at by comparing the normal slide to pictures in histology texts, available at the lab tables.
3. Start to note some of the differences between the normal tissue slide and the cancer tissue slide. Your notes and drawings can be used in answering the questions in the first assignment.
2 4. Time permitting, you may want to move around the lab to see some of the slides representing other cancers and to talk with other students to see how they are approaching the assignment. The cancer slides include
Slide label In lay terms a. fibroadenoma of the breast breast cancer b. Hodgkin’s granuloma Hodgkin’s lymphoma c. carcinoma of the larynx cancer of the larynx d. bronchogenic carcinoma cancer of the bronchus e. adenocarcinoma of ovary ovarian cancer f. basal cell carcinoma skin cancer g. sarcoma of uterus uterine cancer h. adenocarcinoma of endometrium endometrial cancer i. transitional cell carcinoma bladder bladder cancer j. carcinoma of colon colon cancer k. carcinoma of stomach stomach cancer l. carcinoma of esophagus esophageal cancer m. malignant melanoma skin cancer n. carcinoma of prostate prostate cancer o. acute monocytic leukemia leukemia p. squamous cell carcinoma skin cancer q. adenocarcinoma of lung lung cancer r. astrocytoma brain tumor s. alveolar cell carcinoma lung cancer t. adenocarcinoma of breast breast cancer u. acute granulocytic leukemia leukemia v. chronic lymphocytic leukemia leukemia
We will arrange several other times (most likely on Thursday, Friday or an evening) when you can return to the lab to take another look at the slides under the microscope. Also, feel free to consult the instructor as you are working on the assignment for additional text diagrams or for another perspective on the structures you are looking at.
3 4 Bio 207 HistologyWorkshop Questions (20 points)
After completing the workshop, research your answers to the following questions, then briefly print or type your answers on separate pages. Be sure to cite any references you consulted (by author, year, title, volume, pages for journal or book or by URL address for web sources). Due in class by Monday Sept. 12, 2005.
1. Most types of cancers affect epithelial tissues. Why are epithelia most often affected?
2. Describe the major types of epithelial tissues. You may use your own illustrations, if you wish.
The following questions are based on the cancer and normal tissue slides you were assigned during the workshop.
3. For the normal tissue slide you were assigned, determine where in the body (what organ or organ system and the location) it would be found. Describe, draw, or illustrate with images the relationship between the organ and the section you are looking at.
4. Identify the major cell types in the tissue, their organization (if any) and their functions? Which cells in the tissue might be rapidly dividing and thus more likely to become cancerous?
5. Compare your assigned cancer tissue slide to the normal tissue slide. What is the difference? Document in words or illustrations the differences.
6. How far has the cancer progressed? Do you have any evidence from your slide that the cancer has become metastatic? What are some of the limitations of using tissue biopsy and observation of histological slides as a means of detecting and diagnosing cancers?
5