Histology 1

viewing a thin transilluminated specimen; use of dyes and thin sections

specimen placed between two polarizing filters, light striking oriented molecules is rotated and contrasted against background

the ability to rotate polarized light; necessary for polarization microscopy

specimen stained with a fluorescent dye and irradiated with UV light

light rays directed towards the specimen at an angle. Reflected rays pass through the ocular, illuminate specimen; rarely used - primarily used when testing for syphillis

No dyes used, specimen are essentially transparent. Dependent upon light changing speed as it passes through media with different refractive indices; used for observing living cells

similar to phase contrast, but emplys additional prisms and polarizers to generate contrast; useful for visualizing the surface of living cells

a microscope is linked to a computer and monitor, which is used to measure certain cellular features

First step in tissue processing; immersing the tissue in a fixative that permeates the specimen and cross-links macromolecules together. Typically formalin is used, but can also be performed by picric acid, osmium tetroxide, and gluteraldehyde. Tissue shrinkage typically occurs

Second (optional) step of tissue processing. Hard tissue is immersed in an acid solution (typically formic, hydrochloric or nitric acid) to remove calcium salts, softening it an enabling sectioning; usually performed on bone / teeth to make sectioning simpler

Third step of tissue processing. Progressive bathing of sample in more and more concentrated alcohol, removing water from the specimen

Fourth step of tissue processing. Alcohol from dehydration is replaced by a solvent, typically xylene, rendering the tissue transparent, then tissue is infused with melted paraffin

Fifth step of tissue processing. Tissue is encased in paraffin (light microscopy) or plastic resins (ultrathin sectioning or EM) in order to stabilize it when sectioning

Sixth step of tissue processing. Typically carried out using a microtome or a cryostat

Seventh step of tissue processing. Performed prior to staining so the tissue can absorb the stain. Xylene is introduced to dissolve the paraffin, which is then replaced by progressively more dilute alcohol concentrations until only water remains

Infusing colored stains into tissue sections to make identification of cellular structures easier

"base lover" - tissue stains more readily with basic dyes. Typically acidic material (DNA, RNA)

"acid lover" - tissue stains more readily with acid dyes. Typically basic material (proteins and cytoplasmic components)

"eosinophilic" is often used in place of "acidophilic" because eosin readily stains basic materials

change in dye color when reacting to certain tissue constituents; typically seen when concentrated basic dyes are used. Large molecular aggregates form that transmit light differently than is seen with dispersed dye molecules.

Hematoxylin & Eosin

blue - hematoxylin, binds nucleus, acidic regions of cytoplasm and cartilage matrix

pink - eosin, binds basic cytoplasmic regions, collagen, proteinaceous areas

Sudan black

stains lipids black

Periodic acid-Schiff (PAS)

neutral carbohydrates and glycoproteins stain magenta; typically used to demonstrate glycogen, basement membrane material, and mucus. Considered a carbohydrate stain

Alcian blue

acidic carbohydrates (glycosaminoglycans) stain blue. Considered a carbohydrate stain

Silver

fine structures, such as nerve processes and reticular fibers (stains black)

Osmium

stains lipid-containing structures black

Trichrome (Mallory, Masson's)

• dark blue - nuclei
• red - keratin, muscle, cytoplasm
• light blue - collagen

stains applied to increase contrast of previously stained structures (i.e. background staining)

Histochemistry - definition cut off in lecture manual

• Textbook definition:
• Methods for localizing substances in tissue sections by utilizing specific chemical reactions. Meant to form insoluble complexes with the purpose of identifying specific structures within a cell

Immunohistochemistry (immunocytochemistry)

individual molecules are localized via antibodies to those molecules, and enzymes are linked to those antibodies to be stained.

focuses electrons from a heated metallic filament onto a specimen, up to 1000x resolution of light microscopy (between 1/3-3nm resolution). Tissue sections must be very thin. Fixation via gluteraldehyde, osmium tetroxide, paraformaldehyde and potassium permanganate.

generates a 3D image of the surface of a specimen. Requires a thin film of heavy metal atoms to be applied to the specimen. Electron beam is focused over the surface sequentially, reflecting into a detector which generates the image and displays it on a monitor

Joining of sperm and oocyte, typically within the fallopian tube, inducing the second meiotic division in the oocyte. Acrysomal cap of the sperm contains enzymes allowing it to breach the corona radiata and pierce through the zona pellucida into the oocyte

mass of 12 blastomeres (small cells resultant from rapid divisions following fertilization); appears ~3 days after fertilization

Structure developed from the Morula, composed of embryoblast (large mass of cells), blastocystic cavity, and trophoblast (cells surrounding the cavity)

Differentiated elements of the trophoblast following attachment to the uterine wall

Syncytiotrophoblast - incorporates itself into the uterine wall

Cytotrophoblast - lining of the blastocyst

forms during week 2 post-fertilization. Resulting from embryoblastic cavity forming (eventually the amniotic cavity), generating columnar cells lining up against the hypoblast (referred to as epiblastic cells)

Hypoblast - cells lining the surface of the embryoblast, 1/2 of the bilaminar cavity

Epiblast - columnar cells against the hypoblast, adjacent to the amniotic cavity

develop within the syncytiotrophoblast and fill with maternal blood to supply early embryo with nutrion via diffusion

fingerlike extensions of the cytotrophoblast into the syncytiotrophoblast - develops 2 days after the development of lacunar spaces

columnar development of hypoblast cells, forming a thickened circular structure in the bilaminar disc at ~14 days post-fertilization

during the 3rd week of development, the point at which the three germ layers form, resulting in a trilaminar embryonic disc. Signals the start of morphogenesis (development of the body form)

beginning of gastrulation process. Results from epiblast cells proliferating and migrating between the two layers of the bilaminar disc. Eventually regresses by the end of the 4th developmental week, embryo remains bilaminar at the future sites of the mouth and anus

the thickening of the primitive streak at the cranial end

the lengthening of the primitive streak

the end result of the primitive node and primitive groove lengthing and widening the primitve streak

resulting tissue from the epiblast cell migration between the two lamellae. Some mesenchyme will become embryonic mesoderm, some will migrate to replace the hypoblast, forming embryonic endoderm

the epiblast gives rise to three new germ layers through gastrulation, including ectoderm, mesoderm and endoderm

Epidermis / epidermal appendages, the nervous system, eye and inner ear, connective tissue of the head, and the neural crest

peaks of the neural plate; pinch the neural folds together to form the neural tube

skeletal muscle, blood cells, epithelium of blood vessels, visceral smooth muscle, mesothelium (lining of body cavity), reproductive and urinary organs / ureters, most of the cardiovascular system, connective tissue, bones and ligaments of the trunk

thyroid and parathyroid glands, epithelial linings of the respiratory and gastrointestinal tracts + their glandular components, and that of the inner ear

Process resulting in the formation of the neural tube; induced by the development of the notochord

• 1. induce neurulation
• 2. define the long axis of the embryo
• 3. rigidify the embryo
• 4. signal certain cells to develop into axial muscles and bones, as well as elements of the NCS
• 5. form parts of the intervertebral discs

thickening of cells overlying the notochord. Eventually gives rise to CNS and retinas