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Histology of Bone and Cartilage. Dr. Sama ul Haque. Understand the histology of bone. Understand the histology of cartilage. Objectives. Composition of Bones. Collagen: chief organic constituent (protein) Inorganic Calcium Salts: Vitamin D essential for absorption .
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Histology of Bone and Cartilage Dr. Sama ul Haque
Understand the histology of bone. • Understand the histology of cartilage. Objectives
Composition of Bones • Collagen: chief organic constituent (protein) • Inorganic Calcium Salts: Vitamin D essential for absorption
Cells • Osteoblasts: bone building, bone repairing cells in the periosteum and synthesize new matrix (Osteogenesis) • Osteocytes: osteoblast embedded within the bone matrix (mature bone cells) • Osteoclasts: cells that cause absorption of bone or dissolve bone matrix (Osteolysis)
GENERAL STRUCTURE OF BONES A-Outer Surface of BonesPeriosteum • Dense, fibrous membrane covering bone • Contains blood vessels • Essential for bone cell survival and bone formationOuter Surface of Bones • it is a connective tissue containing osteoprogenitorcells. • Bones are covered by a periosteumexcept in areas where they articulate with another bone. In the latter case, the articulating surface is covered by cartilage.
B-Bone Cavities 1-Endosteum • Bone cavities are lined by endosteum, a layer of connective tissue cells that contains osteoprogenitorcells. • The lining tissue of both the compact bone facing the marrow cavity and the trabeculae of spongy bone within the cavity.Theendosteum is often only one cell layer thick and consists of osteoprogenitor cells .
that can differentiate into bone matrix–secreting cells, the osteoblasts, and the bone lining cells called endosteal cells • 2-Bone marrow:- found in the marrow cavity and the spaces in spongy bone contain. • Red bone marrow consists of blood cells in different stages of development and a network of reticular cells and fibers that serve as a supporting framework for the developing blood cells • later stages of growth and in adults, when the rate of blood
In the adult, red marrow is normally restricted to the spaces of spongy bone in a few locations such as the sternum and the iliac crest. Diagnostic bone marrow samples and marrow for • transplantation are obtained from these sites • Yellow marrow :-consists mostly of fat cells. • In response to appropriate stimuli, such as extreme blood loss, yellow marrow can revert to red marrow.
Bones are classified according to shape; the location ofspongyand compact bone varies with bone shape • Spongy and compact bone tissues are located in specific parts of bones. It is useful, then, to outline briefly the kinds of bone sand survey where the two kinds of bone tissue are located. On the basis of shape, bones can be classified into four groups: • • Long bones are longer in one dimension than other • bones and consist of a shaft and two ends (e.g., the tibia
Short bones are nearly equal in length and diameter (e.g.,thecarpal bones of the hand). • • Flat bones are thin and plate like (e.g., the bones of the a [skull cap] and the sternum). • They consist of two layers of relatively thick compact bone with an intervening layer of spongy bone. • • Irregular bones have a shape that does not fit into anyone of the three groups just described; the shape may becomplex(e.g., a vertebra), or the bone may contain air spaces or sinuses (e.g., the ethmoidbone).
Histological or Microscopically Bone tissue is classified as either compact (dense) or spongy (cancellous). If a bone is cut, two distinct structural arrangements of bone tissue can be recognized . A compact, dense layer forms the outside of the bone (compact bone); a spongelike meshwork consisting of trabeculae(thin, anastomosing spicules of bone tissue) forms the interior of the bone (spongy bone). The spaces within the meshwork are continuous and, in a living bone, are occupied by marrow and blood vessels.
Histological or Microscopically Compact bone (dense) • Basic unit of compact bone is an osteon. • Osteocytes within lacunae arranged in concentric circles called lamellae. • This surround a central canal; complex is called Haversian system. • Weight Bearing.
Histological or Microscopically Spongy bone (cancellous) • Contains trabeculae • Found at ends of Long Bones, Ribs, Sternum, Hips, Vertebrae, Cranium • Web-Like Arrangement • Low Stress Areas Where Weight of Bone Would Be a Problem.
In addition to osteocytes, four other cell types are associatedwithbone. • 1-Osteoprogenitor cells are cells derived from mesenchymal stem cells; they give rise to osteoblasts. •2- Osteoblasts are cells that secrete the extracellular matrix of bone; once the cell is surrounded with its secreted matrix,itis referred to as an osteocyte.
3-Bone-lining cells are cells that remain on the bone surfacewhenthere is no active growth. They are derived from those osteoblasts that remain after bone deposition ceases.
4-Osteoclasts are bone-resorbing cells present on bone surfaces where bone is being removed or remodeled (reorganized). or where bone has been damaged. Osteoprogenitor cells and osteoblasts are developmental precursors of the osteocyte. Osteoclasts are phagocytotic cells derived from fusion of hemopoietic progenitor cells in bone marrow that give rise to the neutrophilic granulocyte and monocyte lineages
Immature Bone • Bone tissue initially formed in the skeleton of a developing fetus • It differs from mature bone in:- • 1-mature bone does not display an organized lamellated appearance. On the basis of its collagen fiber arrangement ,such bone is designated nonlamellar. Nonlamellar bone is also referred to as bundle bone or woven bone becauseofthe interlacing arrangement of the collagen fibers.
2-Immature bone contains relatively more cells per unit area than does mature bone. • 3- The cells in immature bone tend to be randomly arranged, whereas cells in mature bone are usually arranged with their long axis in the same direction as the lamellae. • 4- The matrix of immature bone has more ground substance than does the matrix of mature bone. • 5- The matrix in immature bone stains more intensely with hematoxylin,whereasthe matrix of mature bone stains more intensely with eosin.
6-Although not evident in typical histologic sections immature bone is not heavily mineralized when it is initially formed, whereas mature bone undergoes prolonged secondary mineralization. The secondary mineralization of mature bone is evident in microradiographs of ground sections that show younger Haversian systems to be less mineralized than older Haversian systems
7-Immature bone forms more rapidly than mature bone. • 8-Although mature bone is clearly the major bone type in theadultand immature bone is the major bone type in the developing fetus, areas of immature bone are present in adults, especially where bone is being remodeled. Areas of immature bone are common in the alveolar sockets of the adult oral cavity and where tendons insert into bones. It is this
