Lecture 16 Bone Structure PDF

General Histology Course number: 2110104 Lecture 16 Bone Tarek Hamdy Abd-Elhamid, MBBCh. MSc. PhD. Department of Basic Medical Sciences Faculty of Medicine Aqaba Medical Sciences University Aqaba Jordan ...

General Histology Course number: 2110104 Lecture 16 Bone Tarek Hamdy Abd-Elhamid, MBBCh. MSc. PhD. Department of Basic Medical Sciences Faculty of Medicine Aqaba Medical Sciences University Aqaba Jordan  Objectives 1. Recognize the general features & functions of bone. 2. Describe the structure of bone matrix. 3. Recognize periosteum & endosteum.  Bone General features: Bone is a specialized type of connective tissue. Composed of calcified extracellular material, bone matrix, and bone cells; osteogenic cells, Osteocytes, Osteoblasts & Osteoclasts. Bone matrix is vascular. Bone cells can not divide, not even osteoblasts, thus there is no interstitial growth Grow only by appositional growth  Bone resembles cartilage in that: 1. It consists chiefly of extracellular matrix. 2. Its cells are present in lacunae. 3. It is covered with connective tissue sheath called periosteum. 4. Grows by appositional growth.  Bone differs from cartilage in that: 1. It grows only by appositional growth. 2. Bone cells can not divide, not even osteoblasts, therefore, there is no interstitial growth. 3. Its extracellular matrix is calcified; hence, bone is harder and stronger than cartilage. 4. Bone matrix is vascular, and osteocytes still survive in the calcified matrix.  Functions of bone Provides support for soft tissues Protection (protect internal organs) Aids in the movement of the body. Mineral homeostasis (bones act as reservoir of minerals important for the body like calcium or phosphorus) Provides an environment for blood cell production  Structure of bone It is made of: Bone cells: osteogenic cells, osteoblasts, osteocytes & osteoclasts. Bone matrix: is made of calcium-phosphate crystals & collagen fibers forming lamellae of calcified matrix, proteoglycans and glycoproteins. All bones are lined on their internal and external surfaces by layers of connective tissue containing osteogenic cells— endosteum on the internal surface surrounding the marrow cavity and periosteum on the external surface.  Bone matrix Composed of organic and inorganic materials 1. The inorganic materials: Form about 50% of the dry weight of bone matrix. Consist mainly of calcium in the form of hydroxyapatite crystals. Non-crystalline calcium phosphate are also present. The surface of hydroxyapatite crystals are hydrated; this layer of water around the crystal facilitates the exchange of ions between the mineral and body fluids. Other minerals including Mg+, Na+ and K+, bicarbonate and citrate. Decalcification of bone will result in flexible bone like a tendon.  Bone matrix Composed of organic and inorganic materials 2. The organic materials: About 90% of the organic material is type I collagen Collagen fibers are oriented in highly ordered parallel arrays. Also includes proteoglycans and glycoproteins such as osteonectin. The remaining are calcium-binding protein, osteocalcin and phosphatase. Removal of the organic bone matrix will result in fragile bone on handling (egg- shell consistency).  Periosteum A connective tissue covers the external surface of all bones. Like the perichondrium, the periosteum is organized into 2 layers: The outer layer of dense irregular connective tissue (Wheater ’s Functional Histology 2013) with blood vessels, nerves, collagen bundles, and fibroblasts. Bundles of periosteal collagen fibers, called perforating (or Sharpey’s fibers, penetrate the bone matrix, binding the periosteum to bone. The inner region of periosteum is a more cellular layer containing osteoblasts, bone lining cells, and osteogenic cells in direct contact with the bone surface. (Netter's Essential Histology, 2013)  Endosteum Lines the inner surfaces of bone, including marrow spaces of the diaphysis, surfaces of bony trabeculae of spongy bone, and Haversian canals. Contains osteogenic cells and osteoblasts, and bone lining cells but within a sparse, delicate matrix of collagen fibers. (Atlas of Histology with Functional and Clinical Correlations, 1E (2010))  References Cui, D., 2011. “Atlas of histology with functional and clinical correlations.” Lippincott Williams & Wilkins. Mescher, A.L., 2018. Junqueira’s Basic Histology: Text and Atlas, 15th Ed. McGraw Hill. Ovalle, W.K. and P.C. Nahirney, 2013. Netter's Essential Histology: with Student Consult Access. Elsevier Health Sciences. Young, B., Woodford, P., & O’Dowd, G. 2013. Wheater’s functional histology (6th ed.). Churchill Livingstone. Thank you