This is the region of long bone found between the diaphysis and the epiphysis.
Histology of bone (cortical bone) : shotgun histology
Bones that are wider than they are short are known as long bones. Long, small, flat, irregular, and sesamoid are the five forms of bones. Long bones, especially the femur and tibia, bear the brunt of the weight during everyday activities and are important for skeletal mobility. They mainly develop by diaphysis elongation, with an epiphysis at each end of the developing bone. The epiphyses’ ends are coated in hyaline cartilage (“articular cartilage”). Long bones develop longitudinally due to endochondral ossification at the epiphyseal plate. The development of growth hormone (GH), a secretion of the pituitary gland’s anterior lobe, stimulates bone length growth.
The femora, tibiae, and fibulae of the legs; the humeri, radii, and ulnae of the arms; the metacarpals and metatarsals of the hands and feet, the phalanges of the fingers and toes, and the clavicles or collar bones all fall into the long bone group. The human leg’s long bones account for almost half of an adult’s height. The vertebrae and skull are the other main skeletal components of height.
Structure of long bones
Osseous tissue (bone tissue) is unlike any other tissue in the body. Bone is a hard substance, and many of its functions are dependent on it. Bone is versatile in the sense that its form changes to accommodate stresses, as we’ll see later in this chapter. This section will first look at the gross anatomy of bone before moving on to its histology.
The diaphysis and epiphysis are the two major regions of a long bone (Figure 6.3.1). The diaphysis is a hollow, tubular shaft that connects the bone’s proximal and distal ends. The medullary cavity is found inside the diaphysis and is filled with yellow bone marrow in adults. The diaphysis’ outer walls (cortex, cortical bone) are made up of thick and hard compact bone, which is a form of osseous tissue.
The epiphysis (plural = epiphyses) is the broader portion of the bone at each end that is filled with spongy bone, another form of osseous tissue. In certain long bones, red bone marrow fills the gaps between the spongy bones. At the metaphysis, each epiphysis meets the diaphysis. The epiphyseal plate, which is the site of long bone elongation discussed later in the chapter, is found in the metaphysis during development. The epiphyseal plate becomes an epiphyseal line when the bone begins developing in early adulthood (approximately 18–21 years).
Parts of a long bone
The terms osteogenesis and ossification are sometimes used interchangeably to describe the development of bones. During the first few weeks after childbirth, the skeleton starts to develop. The skeletal pattern is established in cartilage and connective tissue membranes by the end of the eighth week after conception, and ossification starts.
Adults’ bones continue to evolve throughout their lives. Also after reaching adult stature, bone formation continues for fracture repair and remodeling to accommodate changing lifestyles. The three cell types involved in the formation, growth, and remodeling of bones are osteoblasts, osteocytes, and osteoclasts. Bone forming cells are osteoblasts, mature bone cells are osteocytes, and osteoclasts break down and reabsorb bone.
The replacement of sheet-like connective tissue membranes with bony tissue is known as intraamembranous ossification. Intramembranous bones are those that are shaped in this way. They contain some of the irregular bones as well as some of the smooth bones of the skull. Connective tissue membranes form the foundation for potential bones. Osteoblasts migrate to membranes and deposit bony matrix all over them. Osteocytes are produced when osteoblasts are surrounded by matrix.
Structure of bone tissue – bone structure anatomy
Overview of Bone Structure The precise composition or organization of individual bone components varies depending on the form of bone and stage of maturation. The same basic elements make up all human bones:
Some bones (such as the frontal and parietal bones) are derived from the neural crest and undergo membranous ossification, while others (such as the sphenoid and occipital bones) are derived from the paraxial mesoderm and undergo endochondral ossification. Bone maturation stages During embryonic development or bone healing, bones are woven together to form primary bone. Via continuous remodeling, the structure of woven bone is disorganized and transformed into ordered tissue of lamellar bone (secondary bone).
The direction of collagen fibers in the extracellular matrix of immature woven bone and mature lamellar bone is a key distinguishing feature. Bone trabecular (spongy or cancellous bone)
Remodeling and healing of the bones
The human skeleton is constantly changing and remodeling. This is valid not only for the replacement of immature woven bone with lamellar bone, but also for the adaptation of adult bones to their unique loads. Remodeling of the bones