The Skeletal System 2024 PDF

The Skeletal System With Bone Ossification The Skeletal System  BONE TISSUE §Is the main constituent of the adult skeleton §Supports fleshy structures and protects vital organs such as those in the cranial and thoracic cavities §It is a site for haematopoiesis (bone marrow) §Bone...

The Skeletal System With Bone Ossification The Skeletal System  BONE TISSUE §Is the main constituent of the adult skeleton §Supports fleshy structures and protects vital organs such as those in the cranial and thoracic cavities §It is a site for haematopoiesis (bone marrow) §Bone tissue is highly vascularized and metabolically very active §It serves as a reservoir of calcium, phosphate etc  BONE CELLS There are Four cell types: 1. Osteoprogenitor cells: Located in the inner cellular layer of the periosteum, lining haversian canals, and in the endosteum. Are derived from embryonic mesenchyme, can undergo mitotic division, and have the potential to differentiate into osteoblasts 2. Osteoblasts (Bone-forming cells): Formed from osteoprogenitor cells. They synthesize the organic component of the matrix and possess receptors for parathyroid hormone. Found where new bone is to be formed  BONE CELLS 3. Osteocytes (Mature bone cells): Are transformed osteoblasts, found in cavities (lacunae) within the matrix, usually seen in mature bone tissue 4. Osteoclasts (Bone-destroying cells) Are multinucleated giant cells derived from fused bone marrow precursors. Are the macrophages of bone They are involved in the resorption and remodeling of bone tissue Osteoclasts are derived from the fusion of bone marrow- derived mononucleated cells  BONE MATRIX § Contain organic and inorganic componets § Bone contains abundant extracellular matrix, which comprises of 25% water, 25% fiber and 50% crystallized minerals The organic component: Constitute approximately 35% of the dry weight of bone It consist of fibers that are almost exclusively type I collegen Type I collagen makes up about 80% to 90% of the organic component of bone  BONE MATRIX Contd. The inorganic component: §Constitutes about 65% of its dry weight, and is composed mainly of calcium and phosphorus along with other components, including bicarbonate, citrate, magnesium, sodium, and potassium § Calcium and phosphorus exist primarily in the form of hydroxyapatite crystals  BONE MATRIX Contd. §Bone is one of the hardest and strongest substances in the body §Decalcified bone (i.e all mineral is removed), retains its shape but becomes flexible and can be bent like a piece of tough rubber §If the organic component is extracted, the mineralized skeleton still retains its original shape, but becomes extremely brittle and can be fractured with ease.  PERIOSTEUM AND ENDOSTEUM §Periosteum consists of an outer layer of collagen fibers and fibroblasts § Bundles of periosteal collagen fibers, called Sharpey's fibers, penetrate the bone matrix, binding the periosteum to bone § The inner, more cellular layer of the periosteum is composed of fibroblast-like cells called osteoprogenitor cells, with the potential to divide by mitosis and differentiate into osteoblasts § External and internal surfaces of bone are covered by layers of bone-forming cells and connective tissue called periosteum and endosteum  TYPES OF BONE TISSUE §Gross cross section shows dense areas without cavities (compact bone), and areas with numerous interconnecting cavities (cancellous or spongy bone) §Under the light microscope, however, both compact bone and the trabeculae separating the cavities of cancellous bone have the same basic histological structure SHOWING COMPACT AND CANCELLOUS BONE  HARVESIAN CANAL SYSTEMS (OSTEON) A typical harvesian system consist of: Central harvesian canal Bone lamellar Lacuna Osteocytes Cannaliculi Volkman’s canal – connecting 2 harvesian canals COMPACT BONE OSTEON OSTEON  Cancellous Bone A stained section of spongy bone consists of slender, pink- staining strands of bone tissue called trabeculae that form a framework enclosing the irregular marrow cavities The marrow cavities are filled with a hematopoietic tissue called red marrow Red marrow consists of developing blood cells and platelets as well as adipose (fat) cells, which appear as small, clear spaces The trabeculae are composed of parallel lamellae that contain lacunae with osteocytes. 1 = Red marrow 2 = Trabeculae Differences between Compact and Spongy Bone  OSTEOGENESIS (Ossification) 2 Types Intramembranous Osteogenesis Endochondral Osteogenesis Stages of intramembranous osteogenesis - Presence of mesenchymal cells at site of bone formation - Region become highly vascular - Some mesenchymal cells lay down collagen fibres - Mesenchymal cells transform into osteoblast  Stages of Intramembranous Osteogenesis Contd. - Osteoblast secreting matrix to embed fibres - Fibres and matrix swell up, forming osteoid - Calcium is deposited in osteoid under influence of osteoblast - Osteoid become calcified forming bone lamella - Another layer of osteoid is laid down by osteoblast, and more lamella is formed, one over another ENDOCHONDRAL OSTEOGENESIS Blood Supply of Bones Nutrient artery Periosteal artery Epiphyseal artery Metaphyseal artery  Growing end of Long Bones In most long bones, the epiphyses do not fuse simultaneously The epiphyses at one end always fuse a few years before the other end The end at which fusion occurs later is called the growing end and is also the end at which secondary centers appear first The growing end is always located opposite the direction of the nutrient foramen  Growing end Contd. The direction of the nutrient foramen is usually remembered by……… ‘’TO THE ELBOW I GO AND TO THE KNEE I FLEE’’ In the milking cow position, the direction of the nutrient foramen is always downwards Where are the growing ends of the humerus, radius, ulna, femur, tibia? CLINICAL ANATOMY Healing of fractures Osteomalacia/ Rickets Osteoporosis Osteopetrosis Bone Tumor/Ganglion Osteopetrosis Bone tumors Ganglion  Complications of Healing None-union Mal-union Delayed union Osteomylitis (infections)  Introduction ………………………………The End