Basics of the Skeletal System and Articulations Learn and - PowerPoint PPT Presentation

Basics of the Skeletal System and Articulations

Learn and Understand • Skeleton is more than just bone • Functions go beyond support • Bone grows upon existing bone or upon existing cartilage, bone never grows by expanding existing bone from within • The pattern of bone growth in the fetus aids in birth • Bones exhibit a trade off between strength and weight • Many joints do not allow movement • Synovial joints incorporate numerous adaptations which protect them from damage even when frequently used

Functions of Bones Seven important functions – Support – Protection – Movement – Mineral storage – Blood cell formation – Triglyceride (fat) storage – Hormone production

Components of Skeletal System • Bone – Compact or cancellous (spongy) • Cartilage – Hyaline – Fibrocartilage – Elastic • Tendons – muscle to bone • Ligaments – bone to bone

Figure 6.1 The bones and cartilages of the Epiglottis human skeleton. Thyroid Larynx cartilage Cartilage in Cartilages in Cricoid external ear nose cartilage Trachea Articular Lung cartilage of a joint Costal cartilage Cartilage in intervertebral disc Respiratory tube cartilages in neck and thorax Bones of skeleton Pubic symphysis Axial skeleton Appendicular skeleton Meniscus (padlike cartilage in knee joint) Cartilages Hyaline cartilages Articular cartilage of a joint Elastic cartilages Fibrocartilages

Hyaline Cartilage and Interstitial Growth Interstitial Growth: An increase in the size of a tissue by cell division within the interior of a part or structure that is already formed Daughter cells

Cells of Bone Tissue Cell Type Location Function Osteo- Periosteum, When stimulated, divide into progenitor endosteum osteoblasts or bone lining cells – “ osteogenic ” cells Osteoblasts Initially on edge Form bone by secreting matrix of existing components which assemble bone, then in outside of blasts and matrix (become eventually entrap them in hard osteocytes) matrix Osteocytes Lacunae of Monitor and maintain bone bone matrix matrix, stimulate bone remodeling in response to physical stress Osteoclasts Edges of Summoned to an area by (derived from existing bone, osteocytes or signaling macrophages) temporarily chemicals, have ruffled border that uses H + and proteolytic occupy an area enzymes to dissolve bone matrix

Chemical Composition of Bone • Organic components include cells and – Osteoid – up one-third of organic bone matrix – secreted by osteoblasts • ground substance and collagen fibers • Inorganic components – Hydroxyapatites • Makeup 65% of bone by mass • Consist mainly of tiny calcium phosphate crystals • Responsible for hardness and resistance to compression

Figure 6.7 Microscopic anatomy Compact bone Spongy bone of compact bone. Blood & Nervous Supply: good throughout compact bone, indirect supply to cancellous trabeculae Central Perforating (Volkmann’s) canal (Haversian) canal Endosteum lining bony canals Osteon and covering trabeculae (Haversian system) Circumferential lamellae Perforating (Sharpey’s) fibers Periosteal blood vessel Lamellae Periosteum Nerve Vein Lamellae Artery Central Canaliculi canal Osteocyte Lacunae in a lacuna Interstitial Lacuna lamella (with osteocyte)

Figure 6.6 A single osteon. Artery with capillaries Structures Vein in the central Nerve fiber canal Lamellae Collagen Structural unit of fibers compact bone run in Hollow tubes of bone different directions matrix called lamellae • Collagen fibers in adjacent rings run in different directions – Withstands stress – resist Twisting twisting force

Figure 6.4c The structure of a long bone (humerus of arm). Endosteum Periosteum • White, double-layered membrane • Covers external surfaces Yellow bone marrow except joint surfaces • Outer fibrous layer of Compact bone dense irregular connective Periosteum tissue Perforating (Sharpey’s) – Sharpey's fibers secure to fibers bone matrix Nutrient • Many nerve fibers and arteries blood vessels • Anchoring points for tendons and ligaments

Figure 6.4a The structure of a long bone (humerus of arm). Articular cartilage Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Epiphyseal line • Remnant of childhood bone growth at epiphyseal plate Distal epiphysis

Figure 6.3 Flat bones consist of a layer of spongy bone sandwiched between two thin layers of compact bone. Spongy Bone • Trabeculae Spongy bone – Align along lines of stress to (diploë) help resist it Compact – No osteons bone – Contain irregularly arranged lamellae and osteocytes interconnected by canaliculi Trabeculae of spongy bone – Capillaries in endosteum supply nutrients

Bone Development • Ossification (osteogenesis) – Process of bone tissue formation – Formation of bony skeleton • Embryonic skeleton ossifies predictably • Begins in 2 nd month of fetal development – Most long bones begin ossifying by 8 weeks – Primary ossification centers by 12 weeks • At birth, most long bones well ossified (except epiphyses) • At age 25 ~ all bones completely ossified and skeletal growth ceases – Bone remodeling and repair • Lifelong

Approximate size of a human conceptus from fertilization to the early fetal stage Embryo 1-week 3-week 5-week embryo Fertilization conceptus embryo (10 mm) 8-week embryo (3 mm) (22 mm) 12-week fetus (90 mm)

Bone Development: Two Types of Ossification Intramembranous ossification Bone develops from fibrous connective tissue membranes 1. Ossification centers appear 2. Osteoid is secreted 3. Woven bone and periosteum form 4. Lamellar bone replaces woven bone & red marrow appears Forms flat bones, e.g. clavicles and cranial bones Endochondral ossification Bone forms by replacing cartilage (endochondral) bones made of hyaline cartilage Forms most of skeleton

Figure 6.8 Endochondral Birth Childhood to adolescence ossification in a long bone. Articular cartilage Month 3 Secondary ossification Spongy center bone Week 9 Epiphyseal Area of blood vessel deteriorating Epiphyseal cartilage matrix plate cartilage Hyaline cartilage Medullary Spongy cavity bone formation Bone collar Blood vessel of Primary periosteal ossification bud center 1 2 3 4 5 Bone collar Cartilage in the The periosteal The diaphysis The epiphyses forms around the center of the bud invades the elongates and a ossify. When diaphysis of the diaphysis calcifies internal cavities medullary cavity completed, hyaline hyaline cartilage and then develops and spongy bone forms. Secondary cartilage remains model. cavities. forms. ossification only in the epiphyseal plates centers appear in and articular the epiphyses. cartilages.

Lengthening of Long Bones in Childhood and Adolescence • Requires presence of epiphyseal cartilage • Epiphyseal plate maintains constant thickness – Rate of cartilage growth on one side balanced by bone replacement on other • Concurrent remodeling of epiphyseal ends to maintain proportion • Result of five zones within cartilage – Resting (quiescent) zone – Proliferation (growth) zone – Hypertrophic zone – Calcification zone – Ossification (osteogenic) zone

Growth in Length of a Long Bone Occurs at the Epiphyseal Plate Resting zone 1 Proliferation zone Cartilage cells undergo mitosis. 2 Hypertrophic zone Older cartilage cells enlarge. Calcification 3 (a) X-ray image of right knee, anterior zone view. Proximal epiphyseal plate of Matrix becomes the tibia enlarged in part (b). calcified; cartilage cells die; matrix Calcified begins deteriorating. cartilage spicule Osseous 4 Ossification tissue zone New bone is forming. (b) Photomicrograph of (c) Diagram of the zones cartilage in the epiphyseal within the epiphyseal plate (125 x ). plate. Figure 6.12 Growth in length of a long bone occurs at the epiphyseal plate.

Growth in Length of Long Bones • Near end of adolescence chondroblasts divide less often • Epiphyseal plate thins then is replaced by bone • Epiphyseal plate closure – Bone lengthening ceases • Requires presence of cartilage – Bone of epiphysis and diaphysis fuses – Females – about 18 years – Males – about 21 years

Appositional Growth: Growth in Width • Allows lengthening bone to widen • Occurs throughout life • Osteoblasts beneath periosteum secrete bone matrix on external bone • Osteoclasts remove bone on endosteal surface • Usually more building up than breaking down → Thicker, stronger bone but not too heavy

Bone Homeostasis • Recycle 5-7% of bone mass each week – Spongy bone replaced ~ every 3-4 years – Compact bone replaced ~ every 10 years • Older bone becomes more brittle – Calcium salts crystallize – Fractures more easily • Consists of bone remodeling and bone repair

Figure 6.15 Stages in the healing of a bone fracture. Stages of Bone Repair Hematoma External Bony callus callus of spongy bone New Internal blood Healed callus vessels fracture (fibrous Spongy tissue and bone cartilage) trabecula 1 A hematoma forms. 2 Fibrocartilaginous 3 Bony callus 4 Bone callus forms. forms. remodeling occurs.