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Through the Looking Glass - From Stem Cells to Tissues and Organs

Learning Resources The University of Michigan Medical School

Cartilage

Atlas Ch 10, pgs. 172-175 (Cartilage)
Text

Ross and Pawlina (6th ed), Chapter 7 Cartilage, pgs. 198-217, and Chapter 8 Bone, pgs. 218-254

Lab Resources

I. 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. How would changes in relative aggrecan content affect cartilage function?  answer Since aggrecan molecules are negatively charged, they are basophilic. The difference in basophilic staining reflects the relative content of glycosaminoglycan (aggrecan). The glycosaminoglycans are highly negatively charged and highly hydrophilic and occupy a huge volume relative to their mass. The high density of negative charges attracts cations, such as Na+, that are osmotically active, causing a large amount of water to be sucked into the matrix. This creates a swelling pressure, or turgor, that enables the matrix to withstand compressive forces. Cartilage matrix resists compression by this mechanism. A loss of aggrecan would lead to a reduction of turgor in the cartilage and weaken it.   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.

 

Electron Micrograph Wall Charts

#29 HYALINE CARTILAGE WebScope ImageScope

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

#30 CHONDROCYTE (HYALINE CARTILAGE) WebScope ImageScope

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) WebScope ImageScope

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 WebScope ImageScope.

#32 ELASTIC CARTILAGE WebScope ImageScope

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

Review Questions

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

Mature Bone

I. MATURE BONE

Slide 50 (fibula, monkey, decalcified, H&E) WebScope

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 #050   Webscope   ImageScope can the bone shaft can also be seen in this section. What distinguishes between compact and spongy bone?  answerThough it is easy to differentiate between compact and spongy bone at a gross level, at the microscopic level the main difference is the presence or absence of osteons. Grossly, compact bone has a dense appearance and is found, for example, on the outer surfaces of the long bones of the body. As the name implies, spongy bone is shaped like a sponge. The spaces within the sponge-shaped framework are filled with bone marrow. Compact bone, microscopically, is made of numerous osteons, whereas spongy bone is composed of sheets of lamellar bone and does not contain osteons.

Ground sections:
Cross sections:

051 Bone ground section of compact cross Webscope Imagescope
o51XC bone fibula cross Webscope Imagescope
093B Bone ground section of compact bone H&E cross Webscope Imagescope

Longitudinal sections:

093A Bone Ground section of compact longitudinal Webscope Imagescope
051 Bone Ground section of compact longitudinal Webscope Imagescope
051L-EX Bone Ground section of compact longitudinal Webscope Imagescope
093C Bone Ground section of compact bon longitudinal Webscope Imagescope

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 WebScope ImageScope

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 WebScope ImageScope

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 Questions

MatureBO1: What distinguishes between compact and spongy bone? Answer

MatureBO2: Why are blood vessels important in bone? Answer

Practice Questions

  1. In this section of ground bone, the area specifically indicated between the two bars includes: Image

    1. Outer circumferential lamellae
    2. Interstitial lamellae
    3. a Haversian system (osteon)
    4. a Volkmann's canal
    5. Inner circumferential lamellae
  2. answerHaversian system (osteon) - this is a longitudinal section of compact bone showing LONGITUDINAL profiles of osteons consisting of concentric lamellae surrounding central Haversian canals (also in longitudinal profile). The canals that run PERPENDICULAR to the Haversian canals and it do NOT have any concentric lamellae organized around them are Volkmann's canals.
  3. The type of cartilage shown: #040N   Webscope   ImageScope

    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.
  4. answeris highly resistant to compression - the tissue shown is hyaline cartilage. It does NOT always have a perichondrium (as in articular cartilage). Its matrix consists of type II collagen and hyaluronan, and it is NOT found in the pinna of the ear and epiglottis (elastic cartilage is found there).
  5. 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.
  6. answerall of the statements are TRUE, note that statement C is TRUE: the matrix of fibrocartilage does contain type II collagen and some hyaluronan (of course, there's also a lot of type I collagen, but just because it wasn't mentioned does NOT make the statement incorrect).
  7. The cell with its nucleus indicated by the arrow is a/an: #Practice Cartilage 1   Webscope   ImageScope

    1. chondrocyte
    2. chondroblast
    3. osteogenic progenitor cell
    4. osteocyte
    5. connective tissue fibroblast
  8. answerChondroblast - the cell shown is in hyaline cartilage, but it is OVOID and not yet surrounded by a lacuna, so it is a CHONDROBLAST. Osteogenic progenitors are located in the connective tissue perichondrium.