Dichotomous Key for Histology
Dichotomous Key for Histology
A. Does the tissue have a free surface? In other words, is there a continuous sheet of cells which is bounded by other cell tissue on only one side?
No: connective tissue, muscle tissue or nervous tissue (go to B)
Yes: epithelium (continue below)
1. Is there a single, distinct layer of cells?
No: pseudostratified or stratified epithelium (go to 2)
Yes: simple epithelium (continue below)
a. Do the cells appear flat, with little cytoplasm around the nucleus?
No: simple cuboidal or simple columnar epithelium (go to b)
Yes:simple squamous epithelium
b. Do the cells appear square, with a round nucleusnear the center?
No: simple columnar epithelium (go to c)
Yes:simple cuboidal epithelium
c. Do the cells appear rectangular, with an oval nucleus near the middle or toward the side furthest from the free surface? (Note: the nuclei of adjacent cells should be at about the same height.)
No: reconsider the previous options
Yes: simple columnar epithelium (continue below)
(1) Are there cilia at the apical surface?
No:simple columnar epithelium
Yes:ciliated simple columnar epithelium
2. Do the cells appear to be predominantly columnar, but adjacent cells are of different height with nuclei staggered up and down (i.e. some cells do not reach the surface)?
No: stratified epithelium (go to 3)
Yes: pseudostratified columnar epithelium (continue below)
(1) Are there cilia at the apical surface?
No:pseudostratified columnar epithelium
Yes:ciliated pseudostratified columnar epithelium
3. Given that you are looking at stratified epithelium,
a. Do the cells at the apical (free) surface appear flat, with little cytoplasm around the nucleus or with no visible nucleus?
No: stratified cuboidal or stratified columnar epithelium (go to b)
Yes: stratified squamous epithelium (continue below)
(1) Do the cells at the apical surface contain nuclei?
No:nonkeratinized stratified squamous epithelium
Yes:keratinized stratified squamous epithelium
b. Do the cells at the apical surface appear square, with a round nucleus near the center?
No: stratified columnar epithelium (go to c)
Yes:stratified cuboidal epithelium(Note: this tissue is typically two cell layers thick.)
c. Do the cells at the apical surface appear rectangular, with an oval nucleus near the middle or toward the side furthest from the free surface?
No: transitional epithelium (go to d)
Yes: stratified columnar epithelium (continue below)
(1) Are there cilia at the apical surface?
No:stratified columnar epithelium
Yes:ciliated stratified columnar epithelium
d. Do the cells at the apical surface appear dome-shaped (or as a mixture of flat- and dome-shaped)?
No: reconsider the previous options
Yes:transitional epithelium
B. Do you see relatively few cells (nuclei) that appear to be separated by extracellular material? In other words, are adjacent cells separated by other material or by a gap?
No: muscle tissue or nervous tissue (go to C)
Yes: connective tissue or nervous tissue (continue below)
1. Do you see a large cell shaped like a many-pointed star surrounded by many smaller cells?
No: connective tissue (go to 2)
Yes:nervous tissue(i.e. you are looking at the cell body of a neuron surrounded by supporting cells)
2. Do you see concave (or bi-concave) cells with no apparent nucleus?
No: connective tissue proper, cartilage or bone (go to 3)
Yes:blood(i.e. you are looking at red blood cells; it may be possible to identify white blood cells nearby)
3. Are there lacunae (small cavities within the tissue)? There may be cells visible within the lacunae.
No: connective tissue proper (go to 4)
Yes: cartilage or bone (continue below)
a. Are the lacunae arranged in concentric rings (like a target or rings of a tree trunk)?
No: cartilage (go to b)
Yes:bone (or osseous tissue)(i.e. compact bone)
b. Given that, you are looking at cartilage,
(1) Are fibers visible in the matrix?
No:hyaline cartilage(Note: this tissue is also distinguished by a high density of lacunae.)
Yes: elastic cartilage or fibrocartilage (go to (2))
(2) Are the fibers fairly organized with a low density of lacunae?
No:elastic cartilage(Note: this tissue is also distinguished by a high density of lacunae and a ‘‘hairy’’ appearance.)
Yes:fibrocartilage
4. Are there large, round cells with their nuclei pushed to the outside?
No: areolar, reticular or dense connective tissue (go to 5)
Yes:adipose(a form of loose connective tissue made up of fat cells)
5. Are the extracellular fibers loosely packed? In other words, is there a visible amount of space between adjacent fibers?
No: dense connective tissue (go to 6)
Yes: areolar or reticular connective tissue (continue below)
a. Do the fibers form a wide-meshed network, like a fishing net?
No:areolar connective tissue(many overlapping fibers)
Yes:reticular connective tissue
6. Are the extracellular fibers running parallel to one another?
No:dense irregular connective tissue(bundles of collagen fibers running in several directions)
Yes:dense regular connective tissue
C. Do there appear to be hot dog bun-shaped structures lined up end to end?
No: muscle (go to D)
Yes:nervous tissue(i.e. you are looking at a myelinated axon of a neuron)
D. Do the cells lack striations?
No: skeletal or cardiac muscle (go to 1)
Yes:smooth muscle(cells should be spindle- or football-shaped with a large nucleus in the thickest
portion, when viewed in longitudinal section)
1. Do you see intercalated discs? In other words, are the striations occasionally interrupted by a thick ‘‘striation’’ running perpendicular to the length of the cell?
No:skeletal muscle(should have distinct striations and no branching)
Yes:cardiac muscle(cells branch; striations may be difficult to see)