HISTOLOGY BIOL 4000 INTRODUCTION
Basic Terminology Histology : • histos - tissue • logos - study of • So, study of tissue. • Might be better defined as the study of the structure of tissues.
SO WHAT IS THE SCIENCE OF HISTOLOGY?
• Tissue is derived from the French word, tissu which means "weave or texture". • Prior to the late 1700 s, “tissue” did not refer to organic, cellular layers, but rather to anything woven or textured. • So, for example, a fine, lightweight fabric was called a tissue, or a group of connected falsehoods is referred to as a "tissue of lies".
The term “tissue” as it is used in Histology Came into usage in the English language in the late 1700 s Coined by the French scientist Bichat Marie Francois Xavier Bichat (17711802)
It's important to realize that all Bichat’s work was done without a microscope Bichat based his descriptions of tissues on the results of gross dissection (what he saw with his “naked” eyes). Based on such observations, he described 21 “weaves” or “textures” that he called tissues - Bichat’s 21 textures. Other scientists of that period made use of the microscope that had been much improved by the efforts of the Dutch scientist Leeuwenhoek, to delve more deeply into the nature of the weaves or tissues that Bichat had described. Antony van Leeuwenhoek (1632 -1723) http: //home-and-garden. webshots. com/photo/1092738817041241628 b. Wnr. ML
A Brief History of the Microscope: First microscopes were constructed in the Netherlands during the late 1500 s. Actual inventor uncertain, but credit is often given to Zacharias Janssen; however, other possible inventors are Hans Lippershey (inventor of the first real telescope) and Zacharias’ father, Hans Janssen http: //www. southwestschools. org/jsfaculty/Microscopes/history. html Magnification 3 - 9 X, images poor
History of the microscope: 1. First microscope with “high” magnification and good image quality was developed by Anthony van Leeuwenhoek (1633 - 1723) about 1670. 2. Leeuwenhoek used beads formed from drops of molten glass as his lenses. 3. These were mounted in a metal plate that had an adjustable stage on which the specimen to be examined was mounted. 4. Natural light or light from a candle flame was used to illuminate the specimen. http: //www. college-optometrists. org/index. aspx/pcms/site. college. What_We_Do. museyeum. online_exhibitions. microscopy. early/
History of the microscope: Microscope design quickly evolved from better simple microscopes (one lens) to more sophisticated compound (more than one lens in series) models with greatly improved image quality and magnification. http: //www. college-optometrists. org/index. aspx/pcms/site. college. What_We_Do. museyeum. online_exhibitions. microscopy. early/
How a compound microscope works: 1. The specimen is placed on the staged 2. Light is reflected or projected through or onto the specimen. 3. Reflected or projected light from the specimen passes through the objective lenses which magnify the resultant image (e. g. 10 X). 4. The light forming the image from the objective then passes through the eyepiece lenses which again magnify the image (e. g. 10 X). 5. The spacing of the lenses relative to each other and to the specimen and the position of ones eyes acts to focus the image on the retina. 6. In the example above, the magification of the image would be, 10 = 100 X http: //www. yesmag. bc. ca/how_work/microscope. html …… 10 x
Tissues and Cells 17 th century 1670 - Robert Hooke examined cork with a microscope and found it was composed of tiny “chambers”. Hook called these chambers cells because they reminded him of the small rooms or chambers found in monasteries that, at that time, were described by the latin word “cella”. Hooke published this information, as well as the results of other microscopic research he had performed in his Micrographia. http: //www. realcork. org/html/prod_cork_properties. php
Similar compartments were found to be present in animal tissue. Additional study revealed that, in living tissues, these compartments were filled with a fluid substance which is, of course, the cell cytoplasm.
The Cell Theory 1832 - Schleiden and Schwann independently hypothesized that all plant and animal tissues are composed of cells. They believed that cells were the “ultimate” units of living organisms. This is in part correct since cells are the smallest, potentially independent unit of a living organism. MATTHIAS JAKOB SCHLEIDEN 1804 - 1881 However, further study revealed that these small cells contained even smaller structures in their cytoplasm. THEODOR SCHWANN 1810 - 1882
Stains were not used to examine cells in these early studies. Scientists using the microscope relied entirely on differences in refractive index to make structures in tissues visible. This didn’t work very well - not enough contrast Initially only the nucleus (nut) of the cell was noted, but it soon became obvious that there was an even smaller structure within the nucleus that was given the name “nucleolus” which means “small nut”. http: //faraday. physics. uiowa. edu/movies/MPEG/6 a 40. 30. mpg
Various stains were introduced to increase contrast. Basophil - granules contain heparin and histamine.
We now know that all the tissues of the body are formed from 4 basic types of tissue. • Epithelial tissue • Connective tissue • Muscle tissue • Nervous tissue
Definitions • tissues - interwoven masses of cells and extra cellular material • cells - living, more or less self-sufficient entities that form tissues. Surrounded by a membrane. • organelles - membrane bound structures within cells (e. g. mitochondria, golgi bodies, lysosomes) • inclusions - various non-membrane bound structures within cells (e. g. glycogen granules) • molecules and atoms - well, hopefully you know what these are
As we have already stated, histology is the study of the structure of tissues. What is meant by structure? • Tissue structure - how cells combine together with extracellular material and each other to form a tissue • Cellular structure - how a cell is shaped, and how the components inside cells are organized to support that cells specific function • Sub-cellular structure - detailed analysis of organelles and inclusions and finally,
• Histochemical structure - molecular analysis of cellular structure 1. Energy storage molecules - lipid, protein, carbohydrate - energy for cell metabolism. 2. Structural molecules - such as phospholipids and cholesterol, proteins such as tubulin, actin, myosin, etc. Raw materials for synthesis and construction of enzymes, membranes, microtubules, micro-filaments, organelles, cells, etc. 3. Information molecules - DNA, RNA 4. Catalysts, reaction initiators - special proteins called enzymes. 5. Antigenicity - interaction of cell molecular structure with proteins called immunoglobulins (antibodies - the immune system)
Tissues, Cell Theory, Stains, Structure: Put it all together - you get Histology, a science: Friedrich Gustav Jacob Henle (18011885) - credited with creating the first “histology” that was based on a detailed examination of tissues with the microscope, 1838 - presented report on epithelia in the human body. Demonstrated that all internal and external surfaces of the body were covered by epithelia.
Henle developed a classification for epithelia: pavement - squamous cylindrical - cuboidal or columnar ciliated - having cilia Also recognized that the epithelium lining the bladder changed shape as the bladder filled - what we call a transitional epithelium today. Was also an anatomist and cytologist - many anatomical, tissue and cellular structures are named after him. e. g. loop of Henle
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