Cartilage

OBJECTIVES:

1. Be able to recognize the three major cartilage types in typical light microscopic sections.
2. Be able to use standard nomenclature to describe a section of cartilage (e.g. chondrocyte, lacuna, matrix, perichondrium).
3. Understand the molecular basis for resilience of cartilages.
4. Be able to describe the process of chondrogenesis.

I. Hyaline cartilage

hyalos = glass (Greek)

020 trachea connective tissue fibroblast plasma cell H&E Webscope Imagescope
040 trachea H&E Webscope Imagescope
040N hyaline cartilage 1.5um section H&E Webscope Imagescope
126 treachea, esophagus treachea, esophagus H&E Webscope  Imagescope

These slides are good examples of mature hyaline cartilage with its abundant matrix and spaces, lacunae, occupied by cells, chrondocytes, which usually shrink extensively during fixation.  The staining of the matrix is variable. Remember that there are abundant type II collagen fibrils in the matrix. However, they are too small to be resolved in the light microscope, so the matrix has an amorphous, glassy (or “hyaline”) appearance.   The predominately basophilic staining of the matrix in slide #126 reflects preservation of the negatively charged aggrecan molecules in the matrix. Note that the basophilia varies and some interterritorial matrix is eosinophilic reflecting loss (or minimal content) of negative charges, whereas the territorial matrix (the area immediately surrounding each lacuna) is much more basophilic. The differential staining of the territorial matrix compared to the interterritorial matrix is perhaps best shown in slide 40n. The staining actually reflects the relative content of aggrecan. Try to find an area where the cartilage has not pulled away from its investing fibrous perichondrium.  In regions where there is no separation, you can see the stages of chondroblast entrapment #040   Webscope   ImageScope into the matrix (arrested at this point, the cartilage is no longer growing) and the eventual enlargement and rounding of the lacunar space.  Look for cell clusters, isogenous groups. For more practice in recognizing hyaline cartilage, look at the nasal septum in slide #124 124 Webscope Imagescope  .

II. Elastic cartilage

044 Ear pinna Masson Webscope Imagescope
UCSF 153 ear pinna Webscope Imagescope
044H epiglottis H&E Webscope  Imagescope

Slides #44 and UCSF #53 are from the pinna of the ear stained with aldehyde fuchsin and Masson’s trichrome (#44) or elastic van Gieson’s stain (UCSF #53).  In slide #44 stained with aldehyde fuchsin, note the extensive, dark purple elastic fiber network within the cartilage matrix. In slide #53, the elastic fibers stain black whereas the rest of the matrix is yellow-brown. Elastic cartilage can be readily identified in routine H&E sections as well as shown in slide #44H which is from the epiglottis. Look for the plates of elastic cartilage found just under the glands deep to the respiratory epithelium. Observe that there are chondrocytes within lacunae just as in hyaline cartilage, but note the eosinophilic, fibrillar matrix due to the presence of elastic fibers. As with hyaline cartilage, fibrils of type II collagen are present, but they cannot be seen in the light microscope.  You may also notice that elastic cartilage tends to be more cellular than hyaline cartilage.  You can only convincingly identify the elastic cartilage when the section is specifically stained for elastin.

III. Fibrocartilage

045 Intervertebral disc H&E Webscope  Imagescope

This cartilage is named for its textured matrix; it looks fibrous, and in addition lacunae can be seen.  Locate the nucleus pulposus (clear area) of the intervertebral disc, then move out to the edge of the section to see fibrocartilage #045   Webscope   ImageScope .  Note the fibrous texture of the matrix due to the presence of type I collagen fibers in addition to the type II collagen present in all cartilage tissue (type II fibrils are not bundled into fibers large enough to be visible in the light microscope), but note also the distinct chondrocyte lacunae.  Also, note that there is no perichondrium in this cartilage.