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At least 325 records · Page 18Linked to original sources
PubMed2004

Distribution of tenascin-C and -X, and soft X-ray analysis of the mandibular symphysis during mandible formation in the human fetus.

In the development of the human mandible, the process of bone calcification, distribution and expression of tenascin-C and -X in the mental symphyseal region are unknown. The purpose of this study was to determine the distribution of these extracellular matrices in the connective tissue around calcified tissues located on the mental symphyseal region of the human fetus during development through histological and radiographical studies. The radiographic density increased from 16 weeks to 24 weeks gestation in all examined regions; in contrast, the diameter of muscle fiber in the suprahyoid muscles (digastric anterior and geniohyoid muscles) inserted into the inner mental symphyseal region increased from 24 weeks gestation. The extracellular matrices (tenascin) were shown to have a different distribution in the mental symphyseal region of the human fetus at each stage. These different distributions of tenascin-C and -X were found around the epithelium and the endomysium of the mental symphyseal region, and affect the specific formation of the mandible during ossification with hyoid muscle development in human fetus.

Calcification, Physiologic↗
PubMed1999

Hormone regulation of chondrocyte differentiation and endochondral bone formation.

Endochondral bone formation, the formation of calcified bone on a cartilage scaffold, occurs during skeletal development, post natal growth and during bone remodelling and fracture repair. The epiphyseal growth plates represent classical tissues in which to study the ossification process, which requires two co-ordinated components; progressive chondrocyte differentiation and cartilage neovascularisation. Many gene knockout studies have produced new insights regarding how chondrocyte differentiation and angiogenesis are controlled at the molecular level. Additional genetic studies have produced new information regarding the role of hormones in the regulation of endochondral bone formation. The new challenge for the future is to determine how bone formation and turnover is physiologically regulated and co-ordinated to ensure that skeletal development and growth progresses correctly. This study reviews the emerging data in this quickly growing field which should ultimately provide fundamental insights into the normal control of endochondral ossification.

Animals↗
PubMed1989

Evidence for extrarenal production of 1,25-dihydroxyvitamin during physiological bone growth: in vivo and in vitro production by deer antler cells.

The development of deer antler follows a pattern similar to that described for mammalian endochondral ossification and has been proposed as a suitable model for studies of bone growth. We investigated seasonal changes in the plasma concentrations of 1,25-dihydroxyvitamin D [1,25-(OH)2D] and calcium and the activity of alkaline phosphatase in relation to the antler cycle during 1 yr in 4 captive roe deer and measured these biological parameters in 27 wild roe deer during their antler cycle. A significant elevation of 1,25-(OH)2D in peripheral plasma, with no parallel increase in the concentration of its precursor 25-hydroxyvitamin D, was observed to accompany the rapid growth phase of the antler cycle in captive (P less than 0.001) and wild (P less than 0.025) deer. During the same phase there was a gradient in levels of 1,25-(OH)2D in antler vs. jugular blood (P less than 0.01). In addition, velvet cells in culture proved to have the ability to convert 25-hydroxyvitamin D3 into a more polar derivative, which was indistinguishable from true 1,25-(OH)2D3 with regard to its chromatographic properties, its UV absorbance at 254 nm, and its ability to bind to the 1,25-(OH)2D3 receptors present in chick intestinal cytosol. These in vivo and in vitro results strongly suggest that local production of 1,25-(OH)2D by the antler cells does occur in vivo and may contribute to the increase in plasma 1,25-(OH)2D during bone growth.

Alkaline Phosphatase↗
PubMed1993

Pediatric spinal bone marrow: assessment of normal age-related changes in the MRI appearance.

A retrospective study of 100 children (0-15 years) without known bone marrow abnormality, was performed to elucidate the spectrum of the MRI appearance of spinal bone marrow with age on T1-weighted images at 0.5 T. Fatty marrow distribution and vertebral signal intensity (SI) relative to disk SI were noted in each subject, and allowed the identification of distinctive patterns. The spinal marrow patterns and their relative frequency for different age groups were consistent with the known physiologic conversion from cellular to fatty marrow with age. Between the ages of 0 and 1 year, SI of corporeal ossification centers was similar or lower than SI of adjacent cartilage and disk in 87% of cases. Between the ages of 5 and 15 years, vertebral SI was higher than SI of adjacent disks in 90% of cases. A central or basivertebral zone of high SI consistent with focal fatty marrow was found in 16% and 31% of cases respectively. In conclusion, knowledge of these conversion patterns should serve as a practical aid in the interpretation of MRI examinations of the spine in children.

Adolescent↗
PubMed1995

[Effect of bisphosphonates (HEBP, CL2MBP) on the process of biological mineralization in fresh bone and bone tissue de novo as a result of experimental osteogenesis induction in guinea pigs].

It is known from the literature that bisphosphonates inhibit mineralization process in skeletal tissues. To study in vivo the effects of HEBP (etidronate) and Cl2MBP (clodronate) both on preexisting bone mineral as well as on the early stages of the mineralization process the experimental model of heterotopical bone induction was chosen. Urinary bladder mucosa was used as an inductor of osteogenesis. Using this model it is possible to compare the effects of bisphosphonates on preexisting mineral on ortothopic bones as well as on the early stages of mineral deposition in the newly formed bone induced in heterotopic sites. HEBP and Cl2MBP doesn't inhibit heterotopic bone induction, but HEBP deeply inhibits the mineralization process; the small amount of deposited mineral does not contain crystalline fraction.

Animals↗
PubMed1986

[Variations as a function of time of the ossification of various bony elements of the cranial vault (experimental study in mice)].

Experimentally studied in the Mouse, ectocranial modeling bone processes are linked with stages of neuro-physiological development. More particularly, the weaning period is correlated with a complete change of periosteal growth processes in the cranial vault. This study details the different growth processes that model each bony unit of the cranial vault during the two distinct phases of post-natal development (before and after the weaning). Before the weaning, fast cerebral expansion involves generalised growth processes on the whole cranial vault area. A common pattern of growth is shared by several bones (or parts of bones), each bone showing particularities of growth rythm. The interparietal bone, the supraoccipital bone, and the anterior part of non-orbital frontal bone are excluded of that anatomical set of the cranial vault". After the weaning, bone modeling is dependent to muscular strengths. Local processes become more pronounced than generalised growth processes. Sutural and synchondral differential growth are playing a leading part in the craniofacial morphogenesis.

Aging↗
PubMedDate not supplied

[Eccentric ossification of the femur head epiphysis in hip dislocation; consequences for diagnosis and therapy].

Ossification of the upper femoral epiphysis is dependent on biomechanical laws. In babies with normal hips, the osseous nucleus develops in the centre of the epiphysis. In babies with hip dislocation, however, the altered biomechanical factors result in a different location of the nucleus. Ossification begins in a more lateral and cranial position. After reduction of the dislocated hip, either a second nucleus forms and grows together with the first nucleus, or the eccentric nucleus extends in a caudal direction. Both of these alternatives are physiological processes and should not be confused with necrosis of the epiphysis. The eccentric development of the nucleus is hardly mentioned in the modern literature, but it is of the greatest importance for diagnosis and therapy. Ignorance of the phenomenon of eccentric ossification may lead to a false assessment of the position of the femoral head. This mistaken impression may be heightened by an inappropriate X-ray technique: only by using techniques which take into account that the middle rotation position in children is different from that in adults can mistaken diagnoses and unnecessary operations be avoided. Examples are presented.

Cartilage, Articular↗
PubMed2004

Cartilage canals in the chicken embryo: ultrastructure and function.

In this study the detailed morphology and the function of cartilage canals in the chicken femur are investigated. Several embryonic stages (e 13.5, 16, 19, and 20) are examined by means of light microscopy, electron microscopy (TEM), and immunohistochemistry (VEGF, type I and II collagen). Our results show that cartilage canals originate from the perichondrium and form a complex pattern. Two types of canals are distinguishable: shell canals and communicating canals. Shell canals are in the reserve zone and are arranged in successive layers. Communicating canals spring from the shell canals and pass down into the proliferative zone and into the hypertrophic zone. These canals are conical shaped and are orientated nearly in parallel to the long axis of the femur. Cartilage canals comprise venules, arterioles, capillaries (mature and immature), and undifferentiated mesenchymal cells. No canal wall in the sense of an epithelium is elaborated. VEGF is detected in both types of canals and macrophages are found at the end of the cartilage canals. We conclude that the growth factor stimulates angiogenesis and that the latter cells erode the matrix ahead of the canals and thus enable the advancement of the vessels. The results clearly show that the canal matrix differs from the remaining cartilage matrix. The canal matrix contains type I collagen, few type II collagen fibrils and proteoglycans are lacking. In contrast, in the cartilage matrix type II collagen and proteoglycans are abundant but no type I collagen is found. Communicating canals are surrounded by a distinct layer of type I collagen indicating that osteoid is formed around these canals. Hypertrophic chondrocytes label for type I collagen and it seemed possible that chondrocytes adjacent to the communicating canals differentiate into bone-forming cells. Our results provide evidence that cartilage canals are involved in nourishment of the cartilage as well as in the ossification process.

Animals↗
PubMed1991

Neutral proteases in regenerating bone.

Proteolytic enzymes acting at physiologic pH (neutral proteases) are involved in both the formation and modeling of new bone and the remodeling of mature bone. In endochondral ossification systems such as growth-plate calcification, fracture healing, osteophyte formation, and demineralized bone matrix-induced osteogenesis, neutral proteases are predominantly involved in modifying proteins and proteoglycans in the extracellular matrix in preparation for calcification. These enzymes are of low molecular weight (below 30,000 Mr), are poorly charged, metal ion dependent, and appear to become active only after being released from chondrocytes. These neutral proteases may be distributed to the extracellular matrix in association with matrix vesicles that are derived from chondrocyte plasma membranes. A similar mechanism of calcification may also exist during malignant osteogenesis in an osteosarcoma; however, the cell producing the neutral protease in this lesion is the osteoblast and the matrix being synthesized is osteoid. In remodeling bone, osteoblasts secrete neutral collagenase (as an inactive enzyme) and produce not only additional proteases capable of activating the collagenase but also a collagenase inhibitor. Osteoblast collagenase or neutral protease may act to remove unmineralized osteoid from bone surfaces, thus facilitating its subsequent degradation by osteoclasts. The production of all these factors by osteoblasts appears to be regulated by calciotropic hormones (e.g., parathyroid hormone, 1,25-dihydroxyvitamin D, and calcitonin), possibly in a concerted fashion. Other possible functions of neutral proteases involve direct actions on cells or on specific molecules (growth factors) residing in the extracellular matrix.

Animals↗