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 recognize forming (embryonic) cartilage.
   
   
5. 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 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 shrink badly 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 the matrix. The staining actually reflects the relative content of aggrecan. How would this 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 microsope.  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 see fibrocartilage [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?

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CA2: Are capillaries present in the matrix?

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

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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_20x (compact bone, decalicified, H&E) [WinLab] [Mac] [WinHome] (W pg 194, 10.11)
Slide 50 _40x (compact bone, decalcified, H&E) [WinLab] [Mac] [WinHome]

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). Incremental deposition similar to that which would be present in inner and outer circumferential lamellae [example] can be seen. What distinguishes between compact and spongy bone? (BO7)

Ground sections (W pgs 192-193, 10.9-10.10):
Slide 51 (cross section) [WinLab] [Mac] [WinHome]
Slide 93B (cross section) [WinLab] [Mac] [WinHome]
Slide 93A (long section, thin) [WinLab] [Mac] [WinHome]
Slide 51 (long section, 20x) [WinLab] [Mac] [WinHome]
Slide 51L-EX (long section, 40x) [WinLab] [Mac] [WinHome]
Slide 93C (long section) [WinLab] [Mac] [WinHome]

There are both longitudinal and cross sections. 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. Study the thinnest ground section (#93A) to identify lacunae and canaliculi. (W pg 193, 10.10a; in this figure the tissue is "unstained" but a red dye has been used to illustrate canals, lacunae and canaliculi). 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).

#39 OSTEOCLAST [WinLab] [Mac] [WinHome]

The osteoclast is a very large cell (multinucleated) that sits on the surface of bone matrix. Note the many lysosomes and phagocytic vacuoles. What is the functional significance of these structures? (BO10) Note the proximity of the osteoblast. Remember that bone deposition can take place very near bone resorption. This explains the juxtaposition of osteoclast and osteoblast. Most osteoclasts are thought to arise by fusion of monocyte-macrophages.

#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? (BO11)

Review Question Answers

BO7: What distinguishes between compact and spongy bone?

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BO9: Why do chondrocytes die after they hypertrophy in the epiphyseal plate of the metaphysis?

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BO10: What is the functional significance of lysosomes and phagocytic vacuoles present in osteoclasts?

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BO11: Why are blood vessels important in bone?

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