Skeletal System

Dr. Lubna Nazli

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Objectives

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• Components • Functions of bone• Number of bones• Bone types• Bone structure• Bone classification• Bone ossification• Axial skeleton• Appendicular skeleton• Applied aspects

Skeletal System

• Composed of the body’s bones and associated ligaments, tendons, and cartilages.

• The human skeleton consists of 206 bones.• We are actually born with more bones (about 300), but many fuse together as a child grows up.• These bones support your body and allow us to

move.

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• The longest bone in our body is the femur (thigh bone).

• The smallest bone is the stapes bone inside the middle ear.

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Functions of bone

Bones function in:• Support of soft tissues• Movement• Protection• Mineral homeostasis - calcium and phosphate• Blood cell production - red marrow

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Types of Bone

Cancellous / spongy• Found in marrow cavity• No Haversian systems• Surface lined by

endosteum

Compact• Forms the dense shell

of bones• Has Haversian systems• Outer surface lined by

periosteum• Inner surface lined by

endosteum

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Compact and Spongy Bone Tissue Organization

Bones of the skeleton contain a combination of both types of bone tissue organization.

• Compact bone – dense outer layer

• Spongy bone – honeycomb of trabeculae

filled with yellow bone marrow

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Anatomy of a Typical Long Bone

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Bone structure

• Dense outer layer of compact bone.• Internal spongy

(cancellous) bone• Long bones have

internal marrow cavity

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Bone Classification by Shape

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Classification of Bones:

By Shape• Long bones – longer

than they are wide (e.g., humerus, femur,

ulna, radius, tibia & fibula)

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Flat bones –• thin, flattened, and a bit

curved (e.g.,sternum, ribs and

most skull bones)

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Short bones• Cube-shaped bones of

the wrist and ankle• Eg: carpals & tarsal

bones

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Sesamoid bones Bones that form within tendons. (e.g., patella)

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Irregular bones –• bones with complicated

shapes (e.g: vertebrae and hip bones)

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Bone structure

Typical long bone structure:• articular cartilage• epiphyses (ends) Spongy

bone• diaphysis (shaft) Compact

bone• Metaphysis • periosteum• medullary (marrow) cavity• endosteum

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• Bone is covered by a double-layered membrane known as the periosteum.

• It has an outer fibrous layer of dense irregular connective tissue.

• Inner cellular layer contains osteoprogenitor cells and osteoblasts.

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• Periosteum is richly supplied with nerve fibers, lymphatic vessels and blood vessels.

• These enter the bone of the shaft via a nutrient foramen.

• Periosteum is connected to the bone matrix via strong strands of collagen.(SHARPEY’S fibers.)

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Structure of short, flat and irregular bones

• outer thin plates of periosteum covered

compact bone• inner endosteum

covered spongy bone

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Bone ossification

• Membranous ossification• Cartilaginous ossification

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The skeleton has two parts:• the axial skeleton• the appendicular skeleton.

The axial skeleton includes• the skull,• the hyoid bone,• the vertebral column (spine, sacrum, and coccyx),• the sternum, and the ribs.

Its components are aligned along the long axis ofthe body.

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The appendicular skeleton includesbones of the upper extremities (arms, forearms,

and hands),• the pectoral (shoulder) girdle,• the pelvic (hip) girdle,• the bones of the lower extremities (thigh,

knee, leg, and foot).

Its components are outside the body main axis.

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The Appendicular Skeleton

1.Pectoral girdle2.Upper limbs3.Pelvic girdle4.Male and Female pelvis5.Lower limbs

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Vertebral Column

• Cervical– In neck region

• Thoracic– Posterior to thoracic cavity

• Lumbar– Support lower back

• Sacrum– Five fused sacral vertebrae

• Coccyx– Four fused coccygeal vertebrae

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Vertebral Regions• Cervical

– Neck C1-C7• Thoracic

– Articulate with ribs T1-T12• Lumbar

– Largest and strongest L1-L5• Sacrum

– Triangular bone – 5 fused sacral vertebrae

• Coccyx– Small triangular bone– Usually 4 fused coccygeal vertebrae

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Abnormal Curvatures

• Scoliosis– An abnormal lateral

curvature of the spinal column

– Curvature can occur in an “S” or “C” deviation

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• Kyphosis– An exaggerated dorsal

curvature in the dorsal region

– Common is aged individuals because of osteoporosis

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• Lordosis– Accentuated lumbar

curvature– Being overweight or

pregnant causes an excessive load up front

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Interesting medical facts related to skeletal system!

• Estimating the age and sex of individual.

• In suspicious death the cause of death is known by forensic experts using bones.

• Bone grafts in reconstruction and repair.

• Bone injuries and their complications.

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Applied anatomy

• Fractures• Avascular necrosis• Osteoporosis• Infections• Bone marrow

transplantation

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SDL

• To familiarise with terms describing the features of bones ( condyle, facet, tubercle)

• What is growing end of the bone? Its importance.

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