[Perichordal necroses. Contribution to the understanding of the spinal column morphogenesis]

Chondrocytes form a temporary cartilaginous model by dividing and secreting a thick gel-like extracellular matrix. Once the chondrocytes undergo programmed cell death, osteoblasts enter the site of the cartilaginous model. The process of replacing the temporary cartilaginous model with bone in an ordered manner is called endochondral ossification. In endochondral ossification, not all of the cartilage is replaced by bone tissue. Some cartilage that performs a protective and supportive function...

The upper and lower limb initially develops as a small bulge called a limb bud, which appears on the lateral side of the early embryo. The upper limb bud appears near the end of the fourth week of development, with the lower limb bud appearing shortly after.
Initially, the limb buds consist of a core of mesenchyme covered by a layer of ectoderm. The ectoderm at the end of the limb bud thickens to form a narrow crest called the apical ectodermal ridge. This ridge stimulates the underlying...

Joints form during embryonic development in conjunction with the formation and growth of the associated bones. The embryonic tissue that gives rise to all bones, cartilage, and connective tissues of the body is called mesenchyme.
The mesenchymal stem cells differentiate into chondrocytes that form the hyaline cartilage, and later the cartilaginous model of the bone. This model further transforms into a bone. This process is known as endochondral ossification.
During development, the limbs...

Bone formation, or ossification, begins around the sixth to seventh week of embryonic development. Most bones develop from a cartilaginous template through the process of endochondral ossification. Cartilage formation begins when clusters of mesenchymal cells differentiate into chondrocytes. These chondrocytes proliferate rapidly and secrete an extracellular matrix that becomes encased in a membrane called the perichondrium. The resulting cartilage model provides a template that resembles the...

Degenerative disc disease is a chronic condition in which intervertebral discs gradually lose structure and function. It is not infectious or autoimmune; rather, it results from age-related biochemical and mechanical changes, influenced by genetic, metabolic, and environmental factors.Structure and Function of DiscsThe spine contains 23 intervertebral discs that absorb load, distribute forces, maintain spacing, and allow flexibility. Each disc consists of a nucleus pulposus, a gel-like core...

The symptoms of degenerative disc disease arise from a combination of mechanical compression, vascular compromise, and biochemical inflammation, which together disrupt nerve function and produce pain.Mechanical CompressionDisc degeneration reduces height and elasticity, predisposing to herniation of the nucleus pulposus, a major cause of radicular pain. Herniations may be protrusion (bulging with intact annulus), extrusion (nucleus extends beyond disc but remains connected), or sequestration...