Cartilage and Mature Bone
Slide 1: Hyaline cartilage in the wall of a bronchus. Note the thin perichondrium (white space adjacent to it is an artifact) and pseudostratified columnar epithelium with a thick basement membrane. In the loose CT under the epithelium sharp eyes will be able to pick out bundles of smooth muscle.
Slide 2: Hyaline cartilage and perichondrium (in respiratory system).Here what looks like nuclei in lacunae are really whole, shrunken cells. The territorial matrix is more deeply stained and isogenous groups of chondrocytes are clearly delimited. Ignore the epithelium and CT in the image; they are out of focus (probably because the microscopic section wasn't quite flat).
Slide 3: Hyaline cartilage, plastic-embedded section, toluidine blue-acid fuchsin stain. Chondrocytes show lipid droplets which are often found in mature chondrocytes. Territorial matrix is deeply stained and isogenous groups are easily identifiable.
Slide 4: Tracheal (hyaline) cartilage (and adjacent thyroid above to left) low power. PASH stain (taken from student microscope slides). The dark bands in the cartilage are folds (artifact). The cartilage martrix is very PAS+ (as is the colloid of the thyroid follicles if you are reviewing this at the end of the course).
Slide 5: H.p. of 4 with poor hematoxylin staining. The hyaline cartilage matrix is intensely PAS+. Some of the chondrocytes contain PAS+ glycogen and the connective tissue of the perichondrium is PAS-.
Slide 6: TEM of a chondrocyte of hyaline cartilage. The large cytoplasmic lipid droplet is characteristic of many chrondrocytes in mature cartilage. The matrix has many small chondrocyte processes (small dark structures) in a felt work of thin type II collagen fibers. I vivo the territorial matrix (a small area very close to the plasmalemma) contains a large amount of proteoglycans and less collagen. In preparation of cartilage for EM the proteoglycans collapse and are seen as small (pepper-like) dark dots in the territorial matrix zone which is otherwise light.
Slide 7: SEM & TEM of chondrocytes, CN = cell nest (same as isogenous group). Gl = glycogen. Note that in the TEM micrograph there is no space between the chondrocyte and the matrix (from Kessel and Kardon).
Slide 8: Low power of a section of the end of a long bone showing the articular cartilage towards the joint cavity at the top of the field. Note the lack of a perichondrium.
Slide 9: Some what higher power of articular cartilage and underlying bone (demarcation between the two is sharp). Towards the articular surface chondrocytes are flattened and the matrix contains bundles of banded collagen fibers (as seen in EM - not here). The dark staining at the articular surface is an artifact, not a perichondrium.
Slide 10: Intervertebral disc. Chondrocytes are in rows and between rows the matrix contains large, fairly parallel bundles of collagen fibers. Fibrocartilage is a transition tissue (transition not clearly shown in this image) which lacks a perichondrium and grades into the tissues surrounding it.
Slide 11: LM & EM of fibrocartilage. From Rhodin p. 104. His figure legend:
Fig. 8-11. Fibrous cartilage. Annulus fibrosus. Intervertebral disk. Human L.M.X 250.
Fig. 8-12. Fibrous cartilage. Annulus fibrosus. Intervertebral disk. Mouse. Enlargement of area similar to rectangle in Fig. 8-11. E.M.X 2000.
Fig. 8-13. Chondrocyte. Fibrous cartilage. Enlargement of rectangle in Fig. 8-12. E.M.
Fig. 8-14. Detail of fibrous cartilage. Annulus fibrosus. Intervertebral disk. Mouse. Enlargement of area similar to rectangle in Fig. 8-13. E.M.
Slide 12: Elastic cartilage stained for elastic fibers. The perichondrium would be to the bottom of the field. The chondrocytes, if present, are very shrunken. Many lacunae are empty because the cells fell out during processing.
Slide 13: Old elastic cartilage with few fibers and shrunken chondrocytes.
Slide 14: SEM of a cut open dried long bone (marrow not present). Insert shows the outer compact bone (CB - no not channel 19) and inner cancellous bone (CaB - not a taxi) - which can also be called spongy bone. B.V. are blood vessels which were filled with latex prior to SEM preparation. In the large view it is clear that the trabeculae of spongy bone are irregular and interconnected. Arrows indicate openings where blood vessels (in Volkmann's canals) entered the marrow space in vivo. (From Kessel and Kardon).
Slide 15: A ground section of compact bone (x.s.). Osteons (Haversian systems) and interstitial lamellae are identifiable as are lacunae and canaliculi. Debris (dark brown) fills the space occupied by osteocytes and blood vessels in vivo.
Slide 16: Decalcified section of compact bone (x.s.) stained with H&E. Compare with slide 15. The acid or chelators used to remove the minerals of the bone matrix (so that sectioning is possible) do not preserve cells very well. Thus, most lacunae appear empty and the central canals do not contain very recognizable structures. The lamellar arrangement of the matrix (eosinophilic because of the collagen) is apparent. The irregular white spaces are areas that have been resorbed and are undergoing remodelling. To the top right of the field is a small amount of bone marrow containing 2 adipocytes.
Slide 17: SEM and TEM bone. 1. shows an osteocyte (Os slightly shrunken) with its processes (OP) some of which are seen to penetrate into canaliculi (Ca). BM = mineralized bone matrix and La = lacuna. 2 is a TEM micrograph and shows bone matrix in the process of being mineralized. CF = collagen fibers and asterisks indicate electron dense mineral being precipitated. 3 is a TEM micrograph of an osteocyte (labels as above). The zone (Zo) of labile matrix immediately adjacent to the cell (here devoid of mineral deposits) is indicated (from Kessel and Kardon).
Slide 18: Ground section of compact bone photographed in polarized light. The colors result from the orientation of matrix constituents in adjacent lamellae.
Slide 19: Decalcified compact bone l.s., artifactually separated periosteum. Osteons and a Volkmann's canal entering from the periosteum are also seen.
Slide 20: Compact bone (ground) almost l.s. Lamellae are clear although osteons are not always. Note the two air bubles in Haversian canals.
Slide 21: A very low power slide illustrating both decalcified spongy and compact bone. Compare with slide 14. The marrow here is not hematopoietic and is filled with adipose cells.
Slide 22: A fairly thick section of decalcified spongy bone spicules and hematopoietic marrow. Note the osteocytes and lamellae but the absence of osteons.
Slide 23: Note the flattened endosteum covering the bone surface. If you are reviewing this after studying blood and its development find the megakaryocytes. The marrow also has some adipose cells.
Slide 24: SEM of spongy bone. HL = Howships lacunae (in 1 and 2 the osteoclasts were lost during specimen preparation. OL = osteocyte lacunae (cells also lost during prep). 3 is a light micrograph, Bo = bone, Oc = osteoclast. In 4, the SEM of the surface (probably exposed by breaking the bone) shows 2 osteoclasts in HL and collagen fibers (CL) of the matrix being resorbed. Matrix mineral aggregates not yet resorbed are indicated by arrows. (from Kessel & Kardon).
Slide 25: Decalcified developing bone - osteoclasts eating spicules - no marrow yet. Osteoclasts are multinucleate although a section may only show 2 or 3 nuclei. Note the shrunken osteocytes in their lacunae.
Slide 26: Coronal section of the developing fetal pig lower jaw, low power (see the diagram in the syllabus for orientation). Lateral to the developing tongue musculature Meckel's cartilage is seen as round profile of hyaline cartilage on the medial aspect of the developing intramembranous bone of the mandible.
Slide 27: Very early spicule formation. The osteoblasts are polarized and are beginning to secrete osteoid. Note that osteoblasts are larger and more basophilic than adjacent mesenchymal cells. Gap junctions are formed while the cells are osteoblasts (and are adjacent to each other).
Slide 28: Early spicules with abundant osteoid. Locate osteoblasts, osteocytes and mesenchyme.
Slide 29: More mature spicules than the previous slide. Some have active bone deposition along only part of their surfaces (identifiable because of the presence of robust osteoblasts) while other areas are covered by more inactive (but presumably still potentially osteogenic) flattened cells. Note the thin walled blood vessels many of which contain erythrocytes.
Slide 30: Portion of a spicule with bone deposition on only one surface (with osteoblasts). Note the shrunken osteocytes in their lacunae.
Slide 31: A low power image of the bone of the developing mandible. Examine the spicule closest to the developing tooth and find the large osteoclasts on its inner surface. Note that there is bone deposition (large, active osteoblasts) on its outer surface (towards the periosteum).
Slide 32: A higher magnification illustration of the same process shown in slide 7. Osteoclasts are "eating" a spicule while there are osteoblasts on other surfaces.
Slide 33: A very low power image of the cartilagenous model of the bones of a human fetal hand. Embryonic hyaline cartilage. Some of the phalanges are obliquely sectioned.
Slide 34: Developing human digits. Note the chondrocyte hypertrophy (changes in cell size!) in the center of the two long bone cartilage models.
Slide 35: A developing phalange. No blood vessel invasion is evident yet.
Slide 36: Low power of a developing human fetal hand at a later stage of endochondral osteogenesis. Phalanges have developed areas of calcified matrix (as evidenced by dark purple stained areas) in the region of hypertrophied (and now dead) chondrocytes.
Slide 37: No osteogenic bud or bony collar has formed yet.
Slide 38: Cartilage model with hypertrophy - slightly obliquely sectioned. The darker staining matrix of the beginning periosteal collar (formed intramembranously) can be clearly indentified peripheral to the central hypertrophied region of cartilage.
Slide 39: Intramembraneous ossification produces the bony collar around the cartilage model of a developing long bone. Here it is slightly obliquely sectioned.
Slide 40: A low power of a developing long bone with endochondral ossification extending towards the epiphysis. Cartilage zones of multiplication, hypertrophy, matrix calcification and chondrocyte death can be seen. The center of the diaphysis contains spicules of bone (primary spongiosa which is formed on remnants of calcified cartilage matrix). The calcified cartilage matrix is more deeply stained (red-purple). Note the lack of this calcified matrix in the intramembranously formed periosteal collar and locate the periosteum.
Slide 41: Periosteum, bony collar and primary spongiosa. Note deeply staining calcified cartilage matrix which is absent from the bony collar.
Slide 42: Region of developing epiphyseal disc. Masson Trichome stain. Calcified cartilage matrix is stained more lightly green than the bone deposited upon it. Osteogenic cells and primitive marrow cells are brown. Note the zonation present.
Slide 43: Invasion of an osteogenic bud into the epiphysis.
Slide 44: Epiphyseal plate (disc), ossification in the epiphysis and diaphysis. Note the articular cartilage. At the top right part of the field the developing synovial membrane is adherent to the articular surface (artifact).
Slide 45: Higher mag. of an epiphyseal disc. Note the bone of the epiphysis and the cartilage of the disc. Both diaphysis and epiphysis have hematopoietic marrow.
Slide 46: Mature epiphysis with articular cartilage. Note the sharp demarcation between the bone and cartilage and compare them (cartilage lacks blood vessels -this is the most obvious difference since osteons are not very clear in this epiphyseal bone).
Slide 47: Low power of developing vertebrae and intervertebral discs of a human fetal thoracic vertebral column.
Slide 48: Higher magnification of slide 23 showing the endochondral ossification of the vertebral body and the adjacent formation of the annulus fibrosis of the intervertebral disc.