skeletal system bones and bone tissue

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Skeletal System Bones and Bone Tissue. Skeletal System . Is the framework of the body Provides shape to the body and protection for organs and soft tissues Consists of cartilage, bones, tendons and ligaments Functions Support: B one is hard and rigid, bears body weight - PowerPoint PPT Presentation


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Skeletal SystemBones and Bone TissueSkeletal System Is the framework of the body Provides shape to the body and protection for organs and soft tissues Consists of cartilage, bones, tendons and ligaments

Functions Support: Bone is hard and rigid, bears body weight Cartilage provides firm and flexible support, such as cartilage in nose, external ear, thoracic cage and trachea Ligaments attach bone to bone & hold them together

Protection: Bones of skull protects brain Ribs, sternum, vertebrae protect organs of thoracic cavityFunctions of Skeletal System Movement: Skeletal muscles attach to bones by tendonsContraction of skeletal muscles moves the bones, produce body movement

Storage: Ca and P. Stored then released as needed. Fat stored in marrow cavities

Blood cell production: Blood cells and platelets formation takes place in bone marrow of bones Skeletal Cartilages Basic Structure of Skeletal Cartilage Consists mostly of water accounts for resilience

contains no nerves and blood vessels

Surrounded by double layer of dense irregular connective tissue Perichondrium

Outer layer: Contains fibroblasts

Inner layer: More delicate, has fewer fibers, contains chondroblasts and chondrocytes

Blood vessels and nerves penetrate the outer layer of pericardium but do not enter cartilage matrix

Nutrients diffuse through matrix to reach chondrocytes

Skeletal Cartilages Growth of Cartilage: Cartilage grows in two ways:

Appositional growth Add new matrix and chondrocytes to the outside of tissue

Interstitial growth Chondrocytes within the tissue divide and add more matrix between the cells

Skeletal CartilagesTypes of Skeletal Cartilage: Hyaline, Elastic and Fibrocartilage Hyaline Cartilage: Contains fine collagen fibers in matrix, Include Articular cartilages : cover the ends of bones at movable joints Costal cartilages: connect the rib to sternum Respiratory cartilages: forms skeleton of larynx Nasal cartilages: support external noseElastic Cartilage: Contains collagen and elastic fibers - external ears and epiglottis

Fibrocartilage: Thick bundles of collagen fibers, compressible and tough Found in Menisci and intervertebral discs

Classification of Bones Human skeleton consists of 206 bones And divided into two groups:

Axial Skeleton: Consists of skull bones, vertebral column and rib cage Protect and support body parts

Appendicular Skeletan: Consists of bones of upper and lower limbs and girdles ( shoulder and hip bones) Bones of limbs help in movement

Classification of Bones Bones are classified by their shape as long, short, flat and irregular

Long Bones: Are long and thin Are found in arms, legs, hands, feet, fingers, and toes

Flat Bones Are thin, flattened shape, usually curved Are found in the skull, sternum, ribs, and scapula

Classification of Bones

Irregular Bones Have complex shapes Examples:spinal vertebrae pelvic bones

Short BonesAre small and thickExamples:ankle wrist bones

Bone Structure Three levels of structure:

Chemical GrossMicroscopy

Consists of both organic and inorganic components

Organic components include: Cells ( Osteoprogenitor cells, osteoblasts, osteocytes and osteoclasts) and Osteoid, the organic part of the matrix Osteoid (35%) consists mainly of collagen and proteoglycans

Inorganic components

65% of bone tissue is calcium phosphate crystal called hydroxyapatites, CaPO4 crystals

Chemical Composition of BoneGross Anatomy

Bone MarkingsMost bones contain features on external surface

Depressions and openings along bone surface, passage for blood vessels and nerves

Projections where tendons and ligaments attach and at articulations with other bonesInclude heads, trochanters, spines etc. Bone tissue is classified as woven or lamellar bone based on collagen fibers organization within bone matrixWoven bone. Collagen fibers randomly oriented. First formed During fetal development During fracture repairThen Woven bone is remodeled into lamellar boneLamellar boneMature bone, organized in sheets called lamellae. Collagen fibers are oriented in one direction in each layer, but in different directions in different layers for strength.Bone texturesBone textures Bones, whether woven or lamellar can be classifiedaccording to amount of bone matrix relative to amount of space

Compact bone: Contains dense outer layer, less space

Cancellous or spongy bone: Has less bone matrix & more spaceConsists of interconnecting rods or plates of bones called trabeculae

DiaphysisShaft, long axis of boneMade up of Compact bone Surrounds central medullar or marrow activity Red marrow - blood cell formation Yellow marrow adipose tissueEpiphysisEnd of the boneCancellous boneJoint surface of epiphysis is covered with articular (hyaline) cartilage, cushions the bone ends Epiphyseal plate: growth plate Growth in length occurs at E. plateSeparates epiphysis from diaphysisWhen bone stops growing in length becomes Epiphyseal line

Structure of Long BoneMembranesExternal surface of bone is covered by double layer membrane called PeriosteumFibrous layer Outer fibrous layer is dense irregular connective tissue contains blood vessels and nervesCellular layer Inner single layer of bone cells consists of osteoblasts, osteoclasts, osteochondral progenitor cellsPeriosteum is attached to underlying bone by Perforating or Sharpey`s fibers, made up of collagenPeriosteum provides anchoring points for tendons and ligaments

Structure of Long BoneMembranes

Endosteum: Single layer of cells that lines all internal spaces, such as medullar cavity

Contains osteoblasts, osteoclasts, osteochondral progenitor cells

Structure of Long BoneStructure of Flat, Short, and Irregular BonesFlat BonesNo diaphyses, epiphysesSandwich of cancellous between two layers of compact bone, eg. Parietal bone of skull

Short and Irregular BoneSimilar to structure of epiphyses of long bonesCompact bone that surrounds cancellous bone center with small spaces filled with marrowAre not elongated and no diaphyses

Hematopoietic tissue, red marrow is found in trabeculae of spongy bone of long bones, diploe of flat bones (sternum) and in some irregular bones (hip bones)

Location of Hematopoietic Tissue in BonesMicroscopic Anatomy of BoneFour major type of Bone cellsOsteoblastsOsteocytesOsteoclastsStem cells or osteochondral progenitor cells

Osteoblasts Immature bone cells that secrete organic components of matrix known as Osteoid

Osteoblasts surrounded by bone matrix, as the material calcifies, the cell is trapped in a space called a lacuna

And becomes osteocytes (mature bone cells)

Bone Cells

OsteocytesMature bone cells that maintain the bone matrix Live in lacunae Are between layers (lamellae) of matrixConnect by cytoplasmic extensions through canaliculi in lamellaeDo not divideMaintains protein and mineral content of matrixHelps repair damaged bone

Bone CellsBone Cells

Osteoclasts Giant, mutlinucleate cells

Secrete acids and protein-digesting enzymes

Breakdown bone by dissolving bone matrix

Osteoprogenitor Cells Mesenchymal stem cells that divide to produce osteoblasts

Are located in inner layer of perichondrium, inner layer of periosteum and endosteum

Assist in fracture repair

Bone CellsCancellous (Spongy) BoneConsists of interconnecting rods or plates of bone called TrabeculaeNo blood vessels in trabeculae The space between trabeculae is filled with red bone marrow:which has blood vesselsforms red blood cellsand supplies nutrients to osteocytes

Compact Bone

The basic unit of mature compact bone is Osteon or Haversian system

Osteon is a group of hollow tubes of bone matrix, one placed outside the next

Osteon consists of single central canal and around a canal contains blood vessels

Osteocytes are arranged in concentric lamellaePerforating (Volkmann`s )Canals Perpendicular to the central canalCarry blood vessels into bone and marrow

Circumferential LamellaePresent on outer surface of compact bone Binds osteons together

Interstitial Lamellae Present in between osteons

Compact BoneBone formation during fetal development occurs in two patterns:

Intramembranous ossificationTakes place in connective tissue membrane

Endochondral ossificationTakes place in cartilage

Both methods of ossificationProduce woven bone that is then remodeledAfter remodeling, formation cannot be distinguished as one or otherBone Development Takes place in fibrous connective tissue membrane formed from embryonic mesenchyme cells around the developing brain

Starts at 8th week & completes by age 2

Forms many skull bones, part of mandible, diaphyses of clavicles

Mesenchyme cell in the membrane become osteochondral progenitor cell

Osteochondral progenitor cell forms osteoblast

Intramembranous Ossification

Osteoblast produce bone matrix and collagen fiber

And become osteocyte and develop trabeculae More osteoblast gather around trabeculae and produce more bone Trabeculae join together and form cancellous bone

Intramembranous Ossification

Cells in the spongy cell produce red bone marrow

Cells surrounding the developing bone forms periosteum Osteoblasts from the periosteum on bone matrix produce compact bone

Intramembranous Ossification

Bones of the base of the skull, part of the mandible, epiphyses of the clavicles, and most of remaining bones develop through endochondral ossification



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