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Essentials of Human Anatomy The Skeletal System 1
Chapter 5 Dr Fadel Naim Ass. Prof. Faculty of Medicine IUG 1
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Bone Bones are organs Bones are composed of all tissue types.
Their primary component is osseous connective tissue. The matrix is sturdy and rigid due to calcification (also called mineralization).
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Function of Bones Support: form the framework that supports the body and cradles soft organs Protection: provide a protective case for the brain, spinal cord, and vital organs Movement: provide levers for muscles Mineral storage: reservoir for minerals, especially calcium and phosphorus Blood cell formation: hematopoiesis occurs within the marrow cavities of bones Energy storage (fat in yellow marrow)
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Support and Protection
Bones provide structural support and serve as a framework for the entire body. Bones protect many delicate tissues and organs from injury and trauma.
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Movement Muscles attach to the bones of the skeleton
contract and pull on bone functions as a series of levers.
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Storage of Mineral and Energy Reserves
More than 90% of the body’s reserves of the minerals calcium and phosphate are stored and released by bone. Calcium: needed for muscle contraction blood clotting nerve impulse transmission. Phosphate: needed for ATP utilization structure of nucleic acids (DNA, RNA)
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Hematopoiesis Blood Cell Formation
Blood cell production in red bone marrow located in some spongy bone. Red bone marrow contains stem cells form all of the blood cell types.
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Bone Classification Long Bones Short Bones Flat Bones Irregular Bones
Sesamoid (Round) Bones
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Classification of Bones: By Shape
Long bones – longer than they are wide (e.g., humerus)
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Classification of Bones: By Shape
Short bones Cube-shaped bones of the wrist and ankle Bones that form within tendons (e.G., Patella)
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Classification of Bones: By Shape
Flat bones – thin, flattened, and a bit curved (e.g., sternum, and most skull bones)
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Classification of Bones: By Shape
Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones)
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Classification of Bones
Axial skeleton – bones of the skull, vertebral column, and rib cage Appendicular skeleton – bones of the upper and lower limbs, shoulder, and hip
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Bone Structure - External
Cartilage protection for joints
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Bone Structure - External
Epiphyses Expanded ends of long bones Exterior is compact bone, and the interior is spongy bone Joint surface is covered with articular (hyaline) cartilage location of red bone marrow Epiphyseal line separates the diaphysis from the epiphyses Epiphyse
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Bone Structure - External
Diaphysis Tubular shaft that forms the axis of long bones Composed of compact bone that surrounds the medullary cavity Yellow bone marrow (fat) is contained in the medullary cavity Diaphysis
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Bone Structure - Internal
Spongy Bone- red marrow
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Bone Structure - Internal
Compact bone
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Compact and Spongy Bone
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Bone Structure - Internal
Medullary Cavity-yellow marrow
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Bone Structure - Internal
Epiphiseal Plate “Growth Plate”
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Parts of a Long Bone epiphysis diaphysis compact bone spongy bone
distal proximal diaphysis compact bone spongy bone articular cartilage periosteum endosteum medullary cavity trabeculae marrow red yellow
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Structure of Short, Irregular, and Flat Bones
Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone on the inside Have no diaphysis or epiphyses Contain bone marrow between the trabeculae
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Bone Membranes Periosteum – double-layered protective membrane
Outer fibrous layer is dense regular connective tissue Inner osteogenic layer is composed of osteoblasts and osteoclasts Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina Secured to underlying bone by Sharpey’s fibers Endosteum – delicate membrane covering internal surfaces of bone
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Blood and Nerve Supply of Bone
Periosteal arteries Supply periosteum Nutrient arteries Enter through nutrient foramen Supplies compact bone of diaphysis & red marrow Metaphyseal & epiphyseal aa Supply red marrow & bone tissue of epiphyses
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Bone Markings: Tuberosity – rounded projection
Projections ( Sites of Muscle and Ligament Attachment) Tuberosity – rounded projection Crest – narrow, prominent ridge of bone Trochanter – large, blunt, irregular surface Line – narrow ridge of bone
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Bone Markings: Tubercle – small rounded projection
Projections ( Sites of Muscle and Ligament Attachment) Tubercle – small rounded projection Epicondyle – raised area above a condyle Spine – sharp, slender projection Process – any bony prominence
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Bone Markings: Head – bony expansion carried on a narrow neck
Projections That Help to Form Joints Head – bony expansion carried on a narrow neck Facet – smooth, nearly flat articular surface Condyle – rounded articular projection Ramus – armlike bar of bone
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Bone Markings: Depressions and Openings
Meatus – canal-like passageway Sinus – cavity within a bone Fossa – shallow, basinlike depression Groove – furrow Fissure – narrow, slitlike opening Foramen – round or oval opening through a bone
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The Histologic Types: Compact bone ( cortical)
Spongy bone ( cancellous) Lamellar bone: regular – mature Woven bone: irregular – immature – fetus - fracture Osteoid Callus: fracture healing
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Compact Bone: Haversian system, or osteon – the structural unit of compact bone Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen Haversian, or central canal – central channel containing blood vessels and nerves Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal
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Compact Bone Osteocytes – mature bone cells
Lacunae – small cavities in bone that contain osteocytes Canaliculi – hairlike canals that connect lacunae to each other and the central canal
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Compact Bone:
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Spongy (cancellous) Bone
Does not contain osteons. trabeculae surrounding red marrow spaces
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Cell Types of Bone 4 types of cells in bone tissue
Osteoprogenitor cells: Undifferentiated cells Can divide become osteoblasts Found in inner layer of periosteum and endosteum Osteoblasts: Form matrix & collagen fibers but can’t divide Osteocytes: Mature cells that no longer secrete matrix Osteoclasts: Huge cells from fused monocytes (WBC) Function in bone resorption at surfaces such as endosteum
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Bone Development The process of bone tissue formation, which leads to:
Osteogenesis and ossification: The process of bone tissue formation, which leads to: The formation of the bony skeleton in embryos Bone growth until early adulthood Bone thickness, remodeling, and fracture repair
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Bone Growth - Ossification
Cartilage template laid down. Osteoblasts (bone building cells) located in Ossification Centers.
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Bone Growth - Ossification
Primary Ossification Center in diaphasis. Secondary Ossification Centers in epiphisis.
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Bone Growth - Ossification
Grow toward one another, cartilage remains between them. As long as cartilage remains undamaged, growth can occur.
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Formation of the Bony Skeleton
Begins at week 8 of embryo development Intramembranous ossification – bone develops from a fibrous membrane Endochondral ossification – bone forms by replacing hyaline cartilage
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Endochondral Ossification
Begins in the second month of development Uses hyaline cartilage “bones” as models for bone construction Requires breakdown of hyaline cartilage prior to ossification
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Stages of Endochondral Ossification
Formation of bone collar Cavitation of the hyaline cartilage Invasion of internal cavities by the periosteal bud, and spongy bone formation Formation of the medullary cavity; appearance of secondary ossification centers in the epiphyses Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates
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Stages of Endochondral Ossification
Formation of bone collar around hyaline cartilage model. 1 2 3 4 Cavitation of the hyaline cartilage within the cartilage model. Invasion of internal cavities by the periosteal bud and spongy bone formation. 5 Ossification of the epiphyses; when completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages Formation of the medullary cavity as ossification continues; appearance of secondary ossification centers in the epiphyses in preparation for stage 5. Hyaline cartilage Primary ossification center Bone collar Deteriorating cartilage matrix Spongy bone formation Blood vessel of periosteal bud Secondary ossification center Epiphyseal blood vessel Medullary cavity Epiphyseal plate cartilage Spongy bone Articular cartilage
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Long Bone Growth and Remodeling
Growth in length – cartilage continually grows and is replaced by bone Remodeling – bone is resorbed and added by appositional growth
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Bone Growth in Length Epiphyseal plate or cartilage growth plate
Cartilage cells are produced by mitosis on epiphyseal side of plate Cartilage cells are destroyed and replaced by bone on diaphyseal side of plate Between ages 18 to 25, epiphyseal plates close Cartilage cells stop dividing and bone replaces the cartilage (epiphyseal line) Growth in length stops at age 25
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Remodeling Occurs all the time. Stresses change, bones adapt.
Osteoclasts remove bone, Osteoblasts build bone, Osteocytes maintain bone Mineral deposits in Spongy Bone form to hold the stress best. 5-10% bone / year.
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Osteoclast in lacuna;
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Control of Remodeling Two control loops regulate bone remodeling
Hormonal mechanism maintains calcium homeostasis in the blood Mechanical and gravitational forces acting on the skeleton
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Developmental Aspects of Bones
The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms At birth, most long bones are well ossified (except for their epiphyses) By age 25, nearly all bones are completely ossified In old age, bone resorption predominates
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Fracture A disruption in the integrity of a living bone involving injury to: Bone Bone marrow Periosteum Adjacent soft tissues
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Types of Fractures green stick fissured comminuted transverse oblique
spiral Pathologic Stress Occult
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Fracture Healing Bone is the only tissue in the human body other than liver that heals by regeneration instead of by scarring. For regeneration to occur the bone must be immobilized to allow uninterrupted formation of new bone.
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Fracture Healing Primary healing Secondary healing
Non displaced fractures, fractures with compressive fixation across the fracture site Osteoblasts traverse the fracture site and lay down lamellar bone without forming immature bone when there is direct contact between cortical bone ends Secondary healing No compression across fracture site, motion can occur Fracture callus forms to stop motion, stage of consolidation and remodeling
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Primary Bone Healing
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Secondary Bone Healing
Fracture hematoma (72 hours) Granulation tissue (3-14 days) Callus formation (7-14 days) Ossification (3 weeks- 6 months) Consolidation Remodeling (Up to 1 year)
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Rickets a generalized metabolic bone disorder
characterized by a failure of or delay in calcification of the cartilaginous growth plate in children whose epiphyses have not yet fused. it is primarily a disease affecting endochondral calcification manifests clinically and radiographically with widening and deformation of the metaphyseal regions of long bones
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THE END
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