Chondral Osteogenesis Finger

Proximal phalanx from the finger of a fetus. Section from the zone of cartilage degradation and endochondral osteogenesis.

In the right upper corner, the figure shows the largest cells of the column cartilage. The cells in the subsequent layer are the large voluminous cartilage cells of the initiation zone. The center image shows calcified cartilage ground substance □, which contains islands of primary bone marrow. Young bone tissue (stained light red) is layered onto this perforated layer (primitive spongiosa) like a border. The primary bone marrow [2 contains osteoblasts [3, which are polynucleated cells with all kinds of geometries. The bright red layer in the left corner of the figure is the bony sleeve 0 of the diaphysis, which has been created by membranous osteogenesis. It is covered by a string of osteoblasts. Toward the outside follows the cell-rich layer of the periosteum O.

1 Calcifying cartilage, ground substance

2 Bone marrow

3 Osteoclasts

4 Perichondral bone, bone sleeve

5 Periosteum

Stain: hematoxylin-eosin; magnification: x 65

Chondral Ossification Zones

The same ossification processes that operate in the diaphysis also take place in the postnatal period in the epiphyses. In this figure, the epiphysis is located at the left. It is now interspersed with coarse bone lamellae generated by chondral osteogenesis. The subsequent zone (stained red) is young cartilage, followed by the wide zone of the column cartilage [2. The two layers combined form the epiphyseal space or growth plate, which remains until the end of growth. The interstitial growth of these cartilage cells ascertains an increase in bone length. In the right part of the figure, the bone marrow of the diaphysis can be seen between the newly formed bone lamellae O (cf. 208, p 209,211).

■C 1 Bone lamellae of the epiphysis 4 Large voluminous cartilage cells

Oi 2 Column cartilage 5 Bone marrow of the epiphysis and the diaphysis

^ 3 Bone lamellae of the diaphysis

Stain: alum hematoxylin; magnification: x 20

214 Bone Tissue—Compact Bone

In the first years of human life, the primitive fiber-based soft bone (fibrous bone) is degraded and replaced by lamellar bone. Its structure can be studied

Ol in cross-sections through the compact substance (cortical substance) of a long bone (as represented by the tibia). The concentric layers of compact substance (special lamellae) have central canals (Haversian canals or longitudinal <o canals, canales centrales) and blood vessels (Haversian vessels) H. Bone tubules about 1 cm long (possibly several centimeters long) called osteons [2 are created. Their diameters measure about 250-350|im. The transverse canals, called Volkmann canals (canales perforantes), break through the Haversian lamellar system and interconnect the vessels in the Haversian canals with those of the periosteum. Between osteons are remnants of older, largely degraded bone tubules. They are called interstitial lamellae [3 .The fully differentiated osteocytes (bone cells) are located between the lamellae in the cavities of the ground substance. They have cemented themselves into their extracellular matrix. The light crevices in this preparation are technical artifacts.

1 Haversian canals, vessels 3 Interstitial lamellae

2 Haversian systems, osteons

Stain: Schmorl thionine-picric acid; magnification: x 70

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