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The Skeletal System

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Axial Skeletal System 80 bones forms longitudinal axis of the body

- skull - cranial and facial bones

- auditory ear ossicles

- hyoid bone

- vetebral column - vertebrae, sacrum, and coccyx

- thoracic cavity - ribs and sternum

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Appendicular Skeletal System 126 bones

- bones of the limbs

- pectoral and pelvic girdle

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Functions of the Skeletal System support protection movement storage of minerals blood cell production (hemopoiesis)

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Structure of Bone (long bone)

diaphysis epiphysis metaphysis articular cartilage periosteum medullary canal endosteum epiphyseal line

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Diaphysis shaft long portion of a bone contains medullary cavity

Epiphysis ends of long bones articulate with another joint

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Metaphysis in mature bone - where diaphysis joins

epiphysis in growing bone - includes epiphyseal plate

(where cartilage is replaced by bone)

Epiphyseal Line bony structure replaces epiphyseal cartilage when it appears, bone stops growing

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Articular Cartilage thin layer of hyaline cartilage covering

epiphysis where bone forms a joint with another bone

reduces friction absorbs shock

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Periosteum peri = around / osteo = bone connective tissue membrane around surface of bone Two layers :

- fibrous - outer

(consists of fibroblasts and collagen fibers)

- osteogenic - inner

(contains osteoprogenitor cells) essential for bone growth attachment site for ligaments and tendons

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Medullary Canal space within diaphysis contains yellow marrow in adults

- stores fat

Endosteum lines the medullary canal contains osteoprogenitor cells

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Bone Tissue Histology

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Osteoprogenitor Cells

osteo = bone / pro = precursor derived from mesenchyme can undergo mitosis develop into osteoblasts found in inner portion of periosteum,

endosteum, Volkmann’s (perforating) and Haversian (central) canals

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Osteoprogenitor

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Osteoblasts

osteo = bone / blasts = germ or bud derived from osteoprogenitor cells cells that form bone found on bone surfaces secrete collagen, organic compounds

(matrix)

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Osteoblasts

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Osteocytes

osteo = bone / cyte = cell mature bone cells derived from osteoblasts osteoblasts found on bone surfaces;

become surrounded with matrix and become osteocytes

main cells of bone tissues (matrix) found in lacunae

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Osteocytes

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Osteoclasts

osteo = bone / clasts = to break function in bone resorption important in development, growth,

maintenance, and repair of bone found on bone surfaces

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Osteoclasts

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Compact Bone

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Calcification or Remineralization deposition of mineral salts,

(hydroxyapatite), in framework formed by collagen fibers in they tissues harden

hardness of bone depends on crystallized inorganic mineral salts

organic collagen reinforces and makes bone less brittle

calcification occurs in presence of collagen

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Calcification or Remineralization (cont.)

mineral salts accumulate in microscopic spaces between collagen fibers

mineral salts crystallize and harden after spaces are filled, mineral salts

deposit around collagen fibers salts crystallize and harden

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Calcification or Remineralization (cont.)

bone is not completely solid; it has many small spaces between hardened portions

spaces allow for blood vessels spaces reduce the weight of the bone

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Microscopic Anatomy of Compact Bone Volkmann’s canals (perforating) Haversian canals (central) concentric lamellae lacunae canaliculi osteocytes

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Volkmann’s (perforating) Canals spaces through which blood vessels,

lymphatic vessels and nerves from periosteum penetrate (pathway to outside)

transverse canals

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Haversian (central) Canals run longitudinally through bone connect blood vessels of Volkmann's

canals with vessels and nerves of medullary cavity

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Concentric Lamellae rings of hard, calcified matrix around

Haversian canal

Lacunae

(lacuna = little lake) small spaces between lamellae contain osteocytes

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Osteons of Compact Bone

central canal

lacunae containing one osteocyte

lamellae

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Canaliculi tiny canals radiating in all directions

from lacunae filled with extracellular fluid inside are processes of osteocytes connect with one another and

eventually with central canals (mini circulatory system within the bone)

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Haversian System (osteon)

each central canal surrounding lamellae lacunae osteocytes canaliculi

Many osteons cemented together form adult compact bone

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Compact Bone contains few spaces forms external layer of all bones wall of diaphysis is composed mainly of

compact bone provides protection and support resists stress

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Spongy Bone makes up most of short, flat, and

irregularly shaped bones epiphysis of long bones does not contain true osteons (basic unit

of compact bone) - Haversian system contains osteocytes intercellular material

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Spongy Bone (cont.)

not arranged around osteonic canals consists of numerous branching bony

plates (trabeculae) spaces between trabeculae filled with

red marrow; produces blood cells within trabeculae are osteocytes that lie

in lacunae (small spaces between lamellae)

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Spongy Bone (cont.)

radiating from lacunae are canaliculi blood vessel from periosteum penetrate

through spongy bone spongy bone (hipbones, ribs, sternum,

vertebrae, skull and some long bones) is only site in bone of red marrow and blood cell production (hematopoiesis)

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Bone constantly broken down and rebuilt living tissue