Skeletal System I PDF

SKELETAL SYSTEM –I (Bones) Dr Ajith Sominanda College of Medicine, QU [email protected] Mobile 33808329 Office CMED- H6 Annex - Room 22 Office hours: please email or call me and book a time Expected Learning Outcomes 1. Describe the Structure of the bones Gross and microscopic structure 2....

SKELETAL SYSTEM –I (Bones) Dr Ajith Sominanda College of Medicine, QU [email protected] Mobile 33808329 Office CMED- H6 Annex - Room 22 Office hours: please email or call me and book a time Expected Learning Outcomes 1. Describe the Structure of the bones Gross and microscopic structure 2. List the Functions of bones 3. Outline the classifications of the bones 4. Describe bone Formation & Remodeling Introduction Bone is an ‘organ’ (tissue complex)consisting of following tissues; Osseous (bone) tissue, Dense connective tissue, Cartilage tissue, Adipose tissue & Nervous tissue Bone is a dynamic tissue that is continuously growing, remodeling and repairing by itself Functions of bones Support Protection Assist in movements Mineral homeostasis Hematopoiesis (Blood cell formation) Triglyceride storage Structure of Bones Macroscopic parts of a long bone (such as Humerus) Diaphysis (shaft or body of bone) Epiphysis (proximal and distal ends of bone) Metaphysis (Region between epi and diaphysis) Articular cartilage (a layer of hyaline cartilage covering epiphysis) Periosteum (dense connective tissue that covers bone except articular cartilage) Medullary cavity (middle cylindrical space in diaphysis) Endosteum (thin connective tissue membrane lines the medullary cavity) Structure of Bones Microscopic structure (histology) Bone (osseous) tissue consists of Cells and extracellular matrix Osteoprogenitors (stem cells that divides) Cells Osteoblasts (bone building cells, secrete collagen fibers and other substance that forms matix) Matrix Osteocytes (Main cell type that maintain bone metabolism) Cells: Bone forming cells (derived from bone stem cells); Osteoprogenitors, osteoblasts & osteocytes Cells that cause bone (eating) resorption; Osteoclasts Read about composition of bone matrix & homeostasis of bone minerals (Totora’s Prin. Anatomy & Physiology , Global edition, P148, P163-165) Microscopic structure (histology) cont.. Bone is not a solid mass of tissue but contains spaces. Depend on the distribution of spaces, regions of bone is classified into compact bone and spongy (trabecular) bone A B C Microscopic structure (histology) cont.. Compact bone Contains few spaces but strongest region of bone Composed of repeated cylindrical (concentric lamellae) units called Osteon or Haversian system. Each osteon consists of central canal, concentric lamellae, lacunae (contains osteocytes), canaliculi Osteons are parallel structures to the length of diaphysis Blood vessels, nerves from periosteum penetrate the compact bone through Volkman’s or perforating canals and connect with medullary cavity & central canals. Microscopic structure (histology) cont.. Spongy bone More porous and has no osteons Lamellae are irregular and thus form trabeculae between which the spaces are visible Reduce the weight of skeleton and provide space for blood cell formation. Identify A, B, C, D, E A A E D C B \  Classification of the Bones Long bones are longer than wide – a shaft with two ends (e.g., the femur, humerus, metacarpals, metatarsals etc.). Short bones are cube-shaped (e.g. the carpals, tarsals). Flat bones have thin flattened ‘plate-like’ surfaces (e.g., the skull bones, ribs, sternum, scapula, hipbone). Irregular bones have varied shapes, do not fit into other categories (e.g., the vertebrae, facial bones. Classification of Bones Bone Formation Bone tissue formation is Called Ossification (osteogenesis) Embryonic and Fetal bone formation: Mesenchymal cells (MC) Intramembranous Endochondral ossification Ossification Mesenchymal stem cells within the mesenchymal membrane become A hyaline cartilage osteoprogenitors cells and model is developed then become osteoblasts from MCs and this forming ossification centers cartilages are in skull & facial bones and replaced by bone clavicle formation  Intramembranous ossification Mesenchymal stem cells within the mesenchymal membrane become osteoprogenitors cells and then become osteoblasts forming ossification centers in skull & facial bones and clavicle Endochondral Ossification A hyaline cartilage model is developed from MCs and this cartilages are replaced by bone formation Postnatal Growth of Endochondral Bones During childhood and adolescence Bones lengthen entirely by growth of the epiphyseal plates Cartilage is replaced with bone tissue as quickly as it grows Epiphyseal plate maintains constant thickness Whole bone lengthens As adolescence draws to an end Chondroblasts divide less often Epiphyseal plates become thinner Cartilage stops growing Replaced by bone tissue Long bones stop lengthening when diaphysis and epiphysis fuse X-ray of a child’s hand Dwarfism  Hormonal Regulation of Bone Growth Growth hormone – produced by the pituitary gland Stimulates epiphyseal plates Thyroid & parathyroid hormones – ensures that the skeleton retains proper proportions Sex hormones Promote bone growth Later induces closure of epiphyseal plates Bone Remodeling The physiological process of ongoing replacement of old bone and with the formation of new bone. Involves bone resorption (removal of mineral and collagen fibers) by Osteoclasts and new bone deposition (addition od new collagen and minerals to the matrix) by Osteoblasts  MCQ Question Which of the following bone is ossified by membranous ossification? Answer A. Clavicle B. Radius C. Humerus D. Thoracic vertebra E. Tibia  OSPE Question This is an X-ray of the showing shoulder region and part of the rib cage. What is indicated by the red arrow A. Epiphysis B. Diaphysis C. Marrow cavity D. Compact bone E. Shaft  Thank you Reference Totora’s Principles of Anatomy and Physiology