Ch 5 Skeletal System

7-2

Bone Tissue

• Connective tissue with a matrix hardened by minerals (calcium phosphate)

• Continually remodels itself• Functions of the skeletal system

– support, – protection, – movement, – mineral storage, – blood formation (hematopoiesis)

7-3

• Long bones – levers acted upon by muscles

• Short bones – glide across one another in multiple directions

• Flat bones – protect soft organs

Shapes of Bones

Types of bone tissue

• Compact – dense, made of osteons

• Spongy – porous, made of irregular, needle like trabeculae

7-4

7-5

Structure of a Long Bone

• Shaft (diaphysis)• Enlarged ends (epiphyses) • Epiphyseal plate (growth plate > line)• Compact and spongy bone• Marrow cavity• Articular cartilage• Periosteum • Endosteum

7-6

Structure of a Flat Bone

• External and internal surfaces composed of compact bone

• Middle layer is spongy bone and bone marrow

Compact Bone

• Osteon = basic structural unit– cylinders formed from layers (lamellae) of matrix

around central canal (Haversion canal)– osteocytes in lacunae connected to each other

and their blood supply by tiny cell processes in canaliculi

7-8

Blood Vessels

of Bone

• Perforating canals or Volkmann canals - perpendicularly join central canals

7-10

Bone Cells

• Osteoblasts form organic matter of matrix • Osteocytes are osteoblasts trapped in the matrix

they formed– cells in lacunae connected by gap junctions inside

canaliculi

7-11

Bone Cells

• Osteoclasts develop in bone marrow by fusion of 3-50 stem cells

• Reside in pits that they ate into the bone• Resorb (break down) bone matrix

Matrix of Bone Tissue• Dry weight = 1/3 organic & 2/3 inorganic matter

– Organic matter• Collagen and glycoproteins

– Inorganic matter• 85% hydroxyapatite Ca10(PO4)6(OH)2

• 10% calcium carbonate   CaCO3

• other minerals (fluoride, potassium, magnesium)

• Combination provides strength and resilience

Spongy Bone• Spongelike appearance formed by plates

of bone called trabeculae– spaces filled with red bone marrow

• Trabeculae have few osteons or central canals– no osteocyte is far from blood of bone

marrow

• Provides strength with little weight– trabeculae develop along bone’s lines of

stress

7-14

Spongy Bone Structure and Stress

7-15

Bone Marrow

• In medullary cavity (long bone) and among trabeculae (spongy bone)

• Red marrow like thick blood– reticular fibers and immature cells– Hemopoietic (produces blood cells)– in vertebrae, ribs, sternum, pelvic girdle

and proximal heads of femur and humerus in adults

• Yellow marrow– fatty marrow of long bones in adults

Bone marrow

transplant