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 (W pg 187, 10.1; pg 239, 12.8) hyalos = glass (Greek)

!! If you are a WINDOWS USER on campus, remember to map a drive to the file server (click here), and USE THE [WinLab] LINKS !!

Slide 20 (trachea, H&E) [WinLab] [Mac] [WinHome]
Slide 40 (trachea, H&E) [WinLab] [Mac] [WinHome]
Slide 40N (hyaline cartilage, 1.5um section, H&E) [WinLab] [Mac] [WinHome]
slide 126 (trachea/esophagus, H&E) [WinLab] [Mac] [WinHome]

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 [example] 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. How would changes in relative aggrecan content affect cartilage function? (CA1) 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 [example] 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 [WinLab] [Mac] [WinHome].

II. Elastic cartilage (W pg 189, 10.4)
Slide 44 (ear, pinna, aldehyde fuchsin & trichrome) [WinLab] [Mac] [WinHome]
UCSF Slide 53 (ear, pinna, van Gieson's stain) [WinLab] [Mac] [WinHome]
Slide 44H (epiglottis, H&E) [WinLab] [Mac] [WinHome]

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 (W pg 189, 10.3)
Slide 45 (intervertebral disc, H&E) [WinLab] [Mac] [WinHome]

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 seefibrocartilage [example].  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.

Electron Micrograph Wall Charts

#29 HYALINE CARTILAGE [WinLab] [Mac] [WinHome]

Note the abundance of intercellular matrix. Are capillaries present in the matrix? (CA2) Study the development of chondrocytes from chondroblasts.

#30 CHONDROCYTE (HYALINE CARTILAGE) [WinLab] [Mac] [WinHome]

Note that the collagenous fibrils are partially obscured and lack obvious periodicity. What type of collagen is found in the matrix? (CA3) Note the many cell organelles in this very active chondrocyte.

#31 CHONDROCYTE (FIBROCARTILAGE) [WinLab] [Mac] [WinHome]

Extracellular collagenous fibrils are coarser in fibrous cartilage than in hyaline cartilage, and do show periodicity. (They are made of type I collagen.) Observe the varied directions of collagenous bundles. The amorphous matrix surrounding the chondrocyte helps distinguish this cell from that of a fibroblast in dense connective tissue. For a comparison, check back to chart #23 [WinLab] [Mac] [WinHome].

#32 ELASTIC CARTILAGE [WinLab] [Mac] [WinHome]

Find the elastic components in the matrix. The delicate intracellular filaments are intermediate (vimentin) filaments.

Review Question Answers

CA1: How would differences in the relative content of aggrecan affect cartilage function?

answer

CA2: Are capillaries present in the matrix?

answer

CA3: What type of collagen is present in hyaline cartilage matrix?

answer

OBJECTIVES:

1. Be able to use standard nomenclature to describe the microscopic structure of bone (e.g. lamella, osteon, osteocytes, canaliculi, periosteum, endosteum).
   
   
2. Be able to recognize mature bone (dense and cancellous) in conventional or ground section. Be able to identify the component parts of mature bone (e.g. osteon, lamella, lacuna, osteocyte) in appropriate sections.
   
   
3. Be able to describe the anatomical route that nutrients and metabolic products use between the vascular system and osteocyte.

I. MATURE BONE

Slide 50 (fibula, monkey, decalcified, H&E) [WinLab] [Mac] [WinHome] (W pg 194, 10.11)

Prior to sectioning and staining, this sample was soaked in a weak acid solution thus dissolving the mineralized component of the bone matrix but leaving behind all of the organic components (mostly type I collagen). Even though this section is distorted, you should be able to find osteons in various stages of development, lacunae, and canaliculi (to see canaliculi you will need to use your microscope and the glass slide from your collection --cut down the light by closing down the iris diaphragm to see them). The inner and outer circumferential lamellae [example] can the bone shaft can also be seen in this section. What distinguishes between compact and spongy bone? (MatureBO1)

Ground sections (W pgs 192-193, 10.9-10.10):
Cross sections:

Slide 51[WinLab] [Mac] [WinHome]
Slide 51xc (fibula, human, ground section) [WinLab] [Mac] [WinHome]
Slide 93B [WinLab] [Mac] [WinHome]

Longitudinal sections:

Slide 93A (thin) [WinLab] [Mac] [WinHome]
Slide 51_20X [WinLab] [Mac] [WinHome]
Slide 51L-EX [WinLab] [Mac] [WinHome]
Slide 93C [WinLab] [Mac] [WinHome]

These "ground sections" were prepared by taking pieces of bone and grinding them with abrasives between two glass plates until they are thin enough to be semi-transparent. First, study cross sections (#51, #93B). In these sections, the trapped air bends the light giving a dark image; the mineral and matrix generally transmit the light. You should be able to identify osteons and their subdivisions (as in slide 50), interstitial lamellae, Haversian canals and nutrient canals (Volkmann). Note that the latter canals penetrate osteons without causing new lamellae to be laid down around them. Note that Slide 51xc is also an entire cross section of the fibula, so you should try to compare it against Slide 50 discussed above.

Study the thinnest ground section (#93A) to identify lacunae and canaliculi. (W pg 193, 10.10a). Now, look at the longitudinal sections (#51-20x, #51-40x, or #93C) of compact bone and try identifying the various structures mentioned above, especially Haversian and Volkmann's canals.

Electron Micrograph Wall Charts

#35 OSTEOCYTE [WinLab] [Mac] [WinHome]

The calcium crystals of the bone matrix were removed in this preparation by a decalcification process. Note how coarse the collagenous fibrils are, and the difficulty in visualizing the periodicity of the fibrils (probably due to the process of mineralization).

#40 HAVERSIAN CANAL [WinLab] [Mac] [WinHome]

Note the "inactive" appearance of endosteal cells. The presence of a macrophage in the Haversian canal indicates the potential eroding function of the endosteal lining of the canal. Why are blood vessels so important in bone? (MatureBO2)

Review Question Answers

MatureBO1: What distinguishes between compact and spongy bone?

answer

MatureBO2: Why are blood vessels important in bone?

answer

Practice Questions

Click on the MAC link or PC link to view slide.
1. The cell with its nucleus indicated by the arrow is a/an:

1. chondrocyte
2. chondroblast
3. osteogenic progenitor cell
4. osteocyte
5. connective tissue fibroblast

ANSWER

Click on the MAC link or PC link to view slide.
2. The type of cartilage shown:

1. is highly resistant to compression.
2. is ALWAYS completely invested by a fibrous perichondrium.
3. contains a matrix of type I collagen fibers and hyaluronan.
4. is found primarily in the pinna of the ear and the epiglottis.
5. ALL of the above.

ANSWER

3. Fibrocartilage:

1. is present in intervertebral disks.
2. usually inserts into bone.
3. contains a matrix of type II collagen and hyaluronan.
4. has high tensile strength.
5. ALL of the above.

ANSWER

Click here to view image
4. In this section of ground bone, the area specifically indicated between the two bars includes:

1. Inner circumferential lamellae
2. Outer circumferential lamellae
3. Interstitial lamellae
4. a Haversian system (osteon)
5. a Volkmann’s canal

ANSWER

Produced and supported by:
The Learning Resource Center - Office of Medical Education
Department of Pathology, Virtual Microscopy Facility
Department of Cell and Developmental Biology

Questions or comments? E-mail Dr. J. Matthew Velkey (jvelkey@med.umich.edu)

Except where otherwise noted, this work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.