skeletal system. overview functions classification of bones bone structure microscopic structure of...
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SKELETAL SYSTEM
OVERVIEWFunctionsClassification of bonesBone structureMicroscopic structure of boneFormation of boneJoints
Functions of bone• Bones and cartilage together forms the
skeletal• system performing several functions.• Functions: 1.Support The bones of the legs, pelvic girdle, and
vertebral column support the weight of the erect body. The mandible (jawbone) supports the teeth. Other bones support various organs and
tissues.
Functions of bone2.Protection The bones of the skull protect the brain. Ribs and sternum (breastbone) protect
the lungs and heart. Vertebrae protect the spinal cord.3. Movement Skeletal muscles use the bones as levers
to move the body.
Functions of bone4. Reservoir for minerals and adipose
tissue 99% of the body’s calcium is stored in
bone. 85% of the body’s phosphorous is
stored in bone. Adipose tissue is found in the marrow
of certain bones.4.Hematopoiesis All blood cells are made in the marrow
of certain bones.
Classification of BonesThere are 206 bones in the human
body.They are divided into two large groups: I. Axial skeleton
Forms long axis of the body.Includes the bones of the skull,
vertebral column, and rib cage.Involved in protection, support, and
carrying other body parts.
II. Appendicular skeletonBones of upper & lower limbs and
the girdles (shoulder bones and hip bones) that attach them to the axial skeleton.
Involved in locomotion and manipulation of the environment.
Classification of Bones
Classification of Bones
Four types of bones based on shapes:1. Long Bones Much longer than they are wide. All bones of the limbs except for the
patella (kneecap), and the bones of the wrist and ankle.
2. Short Bones Roughly cube shaped. Bones of the wrist and the ankle
Classification of Bones Types of bones:
3. Flat Bones Thin, flattened, and usually a bit
curved. Scapulae, sternum, (shoulder
blades), ribs and most bones of the skull.
4. Irregular Bones Have weird shapes that fit none of
the three previous classes. Vertebrae and hip bones.
Structure of BoneBones are organs and are composed of
multiple tissue types. Bone tissue (osseous tissue).Fibrous connective tissue.Cartilage.Vascular tissue.Lymphatic tissue.Adipose tissue.Nervous tissue.
Bone StructureExternally bone is covered by a thin layer
of dense connective tissue known as Periosteum.
It is a double-layered membrane• Covers entire external surface of bone
except for joints.• Outer fibrous layer is dense irregular
connective tissue containing fibroblast.• Inner cellular layer contains
osteoprogenitor cells and osteoblasts.• Below compact bone lies more porous and
light weight bone-spongy or cancellous bone.
Bone structureIt is a thin layer found just inside the compact
bone. The centre of the bone shaft is hollow-
Medullary Cavity. This contains both red and yellow bone
marrow
The centre of the bone shaft is hollow-Medullary Cavity.
This contains both red and yellow bone marrow
Endosteum • Delicate connective tissue membrane
covering internal surfaces of bone• Covers the trabeculae of spongy bone in
the marrow cavities and lines the canals that pass through compact bone.
• Contains both osteoblasts and osteoclasts.
Structure of Bone
Bone cells
Bone consist of cells and extracellular matrix.
A. Bone cells1. Osteoblasts
Bone-building cells. Synthesize and secrete collagen fibers
and other organic components of bone matrix.
Initiate the process of calcification. Found in both the periosteum and the
endosteum
Bone cells2. Osteocytes
Mature bone cells. Osteoblasts that have become
trapped by the secretion of matrix. No longer secrete matrix. Responsible for maintaining the
bone tissue.
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3. Osteoprogenitor Cells • Mesenchyme stem cells that divide to
produce osteoblasts• Are located in inner, cellular layer of
periosteum• Assist in fracture repair
4. Osteoclasts Giant, mutlinucleate cells Secrete acids and protein-digesting
enzymes Dissolve bone matrix and release
stored minerals Concentrated in the endosteum. Are derived from stem cells that
produce macrophages
Bone Matrix
Consists of organic and inorganic components.
Organic component • Consists of several materials that are
secreted by the osteoblasts.• Mainly consist of collagen fibers and
other organic materials .• These (particularly the collagen) provide
the bone with resilience and the ability to resist stretching and twisting.
Inorganic component • Consists mainly of two salts: calcium
phosphate and calcium hydroxide that interact to form a compound called hydroxyapatite.
• Bone also contains smaller amounts of magnesium, fluoride, and sodium.
• These minerals give bone its characteristic hardness and the ability to resist compression.
Structure of Long Bone Long bone consist of a diaphysis and an
epiphysis.Diaphysis
Tubular shaft that forms the axis of long bones
Composed of compact bone that surrounds the medullary cavity (central marrow cavity)
In adults, the marrow cavity contains fat - yellow bone marrow.
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Structure of Long Bone Epiphyses
Expanded ends of long bonesExterior is compact bone, and the
interior is spongy boneJoint surface is covered with articular
(hyaline) cartilage that cushions the bone ends and reduces friction during movement.
Microscopic Structure of Compact Bone
In cross section, compact bone is seen to consists of tightly packed multiple cylindrical structural units -osteons or haversian systems.
They are arranged parallel to one another along the long axis of a compact bone.
Osteons/Haversian systemsEach osteon consists of a single central
canal, known as a haversian canal, surrounded by concentric layers of calcified bone matrix (lamella).
Haversian canals are interconnected with one another via Volkmann's canals.
Between the lamella are present concentric rings of fluid filled spaces-lacuna containing osteocytes.
Tiny hair-like channels/canaliculi extend from lacuna through which osteocytes communicate and receive nutrients.
Haversian canals allow the passage of blood vessels, lymphatic vessels, and nerve fibers.
Structure of Bone
Haversian canal system
Microscopic Anatomy of Microscopic Anatomy of BoneBone
Compact Bone
Microscopic Structure of Bone: Compact Bone
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