Textbook Reference: chapter 5 Skeletal System Textbook Reference: chapter 5

Unit ___ Goals Differentiate between the axial and appendicular skeletons Define the 5 functions of bone Differentiate between the 2 types of boney tissue and the 4 classes of bone in the body Identify the microscopic components to bone Differentiate between the 3 types of bone cells Describe the different modes of bone growth and the reasons for such growth Define the need for spinal curvatures and the dangers of excessive curves Define the function of intervertebral discs Describe the reasons for gender differences of bones Identify the major bones of the body and the class to which they belong

The Skeletal System Your skeleton comprises ~ 20% of your total body mass There are 206 bones in your body, separated into 2 divisions: 1. Axial skeleton: head, vertebrae and rib cage 2. Appendicular Skeleton: pelvis, scapulae and limbs

Axial: pink Appendicular: green

5 Functions of Bones Support: legs support the weight of body, ribs support thoracic cavity Protections: protects all soft tissue organs Movement: muscles use bones as levers, allowing for movement Storage: fat stored in internal cavities of bones; calcium and phosphorus also stored Blood Cell Formation: hematopoesis; the production of blood cells within marrow cavities

Bone Types There are two types of bones: 1. Compact bone: dense bone which is smooth and solid; surrounds all bone; appears dense 2. Spongy bone: internal portion of bone; consists of small needle-like projections of bone called trabeculae with many open spaces filled with marrow

Bone Types

Bone Classification Bones come in many shapes and sizes and are classified into 4 distinct groups: Long Bones Longer than wide Built to absorb stress Consists of a shaft and 2 heads at each end Mostly compact but some spongy bone internally Examples: all bones of limbs except patella, carpals and tarsals

Long Bone: the femur

Bone Classification 2. Short Bones Roughly cube-like Contains mostly spongy bone Thin layer of compact bone on surface Examples: carpals and tarsals Sesamoid bone: a bone embedded in a tendon; varies in size and numbers/each individual; act to alter the pull of a tendon; i.e. patella

Short Bones: carpals of the wrist

Bone Classification 3. Flat Bones Thin, flattened and usually curved 2 parallel compact surfaces with a spongy layer between examples: sternum, ribs and skull bones

Bone Classification 4. Irregular Bones Do not fit any other classification Complicated shapes Mostly spongy with thin compact layer Examples: vertebrae and hip bones

Anatomical Structure of a Long Bone Diaphysis: shaft of long bone; walls made of compact bone Periosteum: fibrous sheath that covers long bones Highly vascularized Functions in bone nourishment and attachment sites

Anatomical Structure of a Long Bone Sharpey’s Fibers: connective tissue fibers that secures the periosteum to underlying bone Epiphyses: ends of long bones Enlarged for muscle attachment Predominately spongy bone

Anatomical Structure of a Long Bone Articular Cartilage: covers ends of epiphyses and provides a slippery surface that decrease friction at joint surfaces Medullary Cavity: holds marrow in center of diaphysis Yellow marrow: fat storage in adults, found in medullary cavity Red marrow: found in diaphysis of infants, in flat bones & epiphyses of adults; makes red blood cells

Anatomical Structure of a Long Bone Endosteum: sheath covering medullary cavity

Bone Composition Bone contains inorganic & organic components Inorganic calcium carbonate & calcium phosphate; provides hardness Organic collagen: to further reinforce the matrix

Osteoporosis: brittle bones Normal Spongy Bone Osteoporotic Spongy Bone

Bone Cells: 3 Types Osteoblasts: arise from embryonic cells and found on outer surfaces of adult bones; aid in matrix production Osteocytes: mature bone cells; trapped in lacunae Osteoclasts: secretes substances that dissolve mineral salt crystals

Bone – cell types Note locations of Osteoclasts & osteoblasts “Ruffled” Border

Microscopic Anatomy of Bone Lacunae: cavities in bones where osteocytes are found Lamellae: a circular layer of bone

Microscopic Anatomy of Bone Haversion Canals: a system of interconnecting canals in adults compact one; runs lengthwise through bone, carrying blood vessels and nerves to all areas of bones Canaliculi: tiny canals that connect all the bone cells to the nutrient supply; radiate outward from Haversion Canals

Microscopic Anatomy of Bone Volkmann’s Canals: communication system from exterior of bone to interior; runs at right angle to diaphysis Osteon/Haversion Systems: each haversian canal with lamellae, osteocytes and caniliculi

Haversion Systems

Bone Development Embryonic Skeleton: predominately hyaline cartilage http://www.dailygalaxy.com/my_weblog/images/2008/05/13/human_embryo.jpg

Bone Development Young child to late adolescence: cartilage replaced by bone Epiphyseal Growth Plates: allows for interstitial growth (lengthwise) Cartilage near the epiphyses regenerates Cartilage near the diaphysis hardens to bone eventually they’ll meet, halting lengthwise growth Fontanels: in skull at birth; allows for growth of brain

Epiphyseal Growth Plate

Epiphyseal Growth Plates Growing Adult

Bone Development & Growth

Ossification The replacement of cartilage by bone Cartilage is covered by osteoblasts Cartilage is “eaten” away, leaving the medullary cavity open within the bone

Appositional Growth Outward growth of bone during adulthood Bones change based on calcium levels & muscles acting on the skeleton Decreased blood calcium leads to bone breakdown Increased demand by muscles on bones causes bone to thicken Weight gain also increase bone diameter Adult bone constantly remodels (breakdown & growth) to help maintain homeostasis of blood mineral levels