01 introduction to histology
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Introduction to HistologyHistology DDS 6214 | Kristine Krafts, M.D.
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Course materials
• Website: GeneralHistology.com
• Handouts: available on website
• Virtual microscope: available on website
• Optional textbook: Atlas of Human Histology. A Guide to Microscopic Structure of Cells, Tissues and Organs (Sorenson).
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Why are we studying histology?
• To develop a mental image of the microscopic appearance of cells, structures, tissues, and organs.
• To correlate microscopic appearance with function in health and disease.
• To provide a basis for later study of anatomy and pathology.
• To pass boards.
• Because it’s awesome.
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Where does histology fit in?
• Microscopic anatomy (histology)• Gross anatomy
• Other basic science courses• Biochemistry• Physiology• Microbiology• Pathology• Pharmacology
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Here is some stuff you should know about histology before we get started.
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Tissue comes to the lab fresh or in formalin.
Fresh lung specimen Formalin container for specimen
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The specimen is placed in a “cassette” that goes into an automated processor for tissue fixation.
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The specimen is embedded in paraffin…
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…and then cut into super thin slices.
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The tissue is transferred onto a slide...
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...and then stained and coverslipped.
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So many stains!
• Most tissue specimens are stained with hematoxylin and eosin.
• Most blood smears are stained with the Wright-Giemsa stain.
• Other stains (like silver, PAS, and acid-fast stains) can be used to highlight special cells or features.
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Section of pancreas stained with hematoxylin and eosin
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Hematoxylin stains negatively-charged
things (like DNA) blue.
Eosin stains positively-charged things
(like most cytoplasmic proteins) red.
Hematoxylin (blue) is positively charged. Eosin (red) is negatively charged.
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Section of pancreas stained with hematoxylin only
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Section of pancreas stained with eosin only
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Same section stained with both H & E…WAY BETTER.
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Section of skin stained with hematoxylin and eosin
Collagen stains pink-red
with eosin.
Cell nuclei stain purple with hematoxylin.
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Blood smear stained with Wright-Giemsa stain
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Silver stains are great for fungi (this one is Aspergillus)
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The silver stain also stains reticulin fibers (this is a lymph node).
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The periodic acid-Schiff (PAS) stain highlights sugars (this is a liver section with a lot of glycogen).
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Toluidine blue stain of lymph node (mast cell granules stain violet)
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The acid-fast stain highlights M. tuberculosis organisms.
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So many cell sizes and shapes!
• The biggest cells are motor neurons, which can be up to 80 µm in diameter.
• Most cells are somewhere between 10 and 30 µm.
• Some cells are quite small (red cells are about 7 µm).
• Cell shapes vary from round to hexagonal to flat.
• Nuclear shapes and locations vary too.
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Motor neurons (about 50-80 µm)
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Red blood cells (about 7 µm)
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Hepatocytes (about 25 µm)
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Red blood cells
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Lymphocytes (about 9 µm)
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Red cells
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Motor neurons and their nuclei
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Adipocytes and their nuclei
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Something else to remember: slides show 2D images of 3D structures
Hollow ball and tube Solid ball and cylinder
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Aspergillus is a long, branching organism
Lengthwise cuts
Cross-sections
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Histologic Hierarchy
Cells
Tissues
Organs
Organ systems
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A few more terms
Tissues are composed of: • Cells • Extracellular matrix
Organs are composed of:• Parenchyma (the cells that perform
the main function of organ)• Stroma (supporting tissue)