19 sept. 2012bone_tissue.ppt1. 19 sept. 2012bone_tissue.ppt2 bones and skeletal tissues skeletal...

19 Sept. 2012 Bone_tissue.ppt 1


BONES and SKELETAL TISSUES

Skeletal System:

a framework, foundation for body &

solid support for soft organs


Skeletal System

• FUNCTIONS in order evolved

– 1. PROTECTION

– 2. LOCOMOTION

– 3. SUPPORT

– 4. STORAGE

– 5. PRODUCTION

Slide 6

Fig. 27.5, p. 458


Skeletal tissues

• Hyaline cartilage• Fibrocartilage• Elastic cartilage• Bone tissue


Structure of Bone Tissue • Bone as connective tissue

– Cells, osteocytes, separated by extracellular matrix

– Collagen fibers, • provide tensile strength

– Extracellular matrix• solid mineral salts (Calcium phosphate)

– “hydroxyapatite”

• Provides hardness, resistance to bending

• about 65% of bone weight


Structure of Bone Tissue • Compact bone• Spongy bone


Structure of Bone Tissue• Compact bone

– Hard, densely calcified “typical bone”

– Living tissue with blood supply, nerves

– Organized of osteons


Structure of Bone Tissue

• Compact bone– Osteon

• Central (Haversian) canal at center

• Osteocytes in lacunae surrounding Haversian canal

• Lamellae of bone matrix between rings of osteocytes


Structure of Compact Bone– Osteons can’t fit together

• Interstitial lamellae fill space to make solid structure

• Circumferential lamellae fill space to shape outer surface of bone


Structure of Spongy Bone

• Spongy bone– Trabeculae

• Irregular thin plates & struts of hydroxyapatite with osteocytes

– Spaces between filled with marrow (yellow or red)

Formation of Bone: Ossification

• Two mechanisms– Intramembranous

ossification

– Endochondral ossification

• No difference in final result.



Intramembranous ossification

• Begins in embryonic mesenchyme membranes

• Mesenchyme cells become osteoblasts

• Begin laying down matrix (osteoid)


Intramembranous ossification

• Layer of “woven bone” and periosteum

• Remodeling to form compact bone on surfaces

• Cranial & facial bones, mandible, clavicles.


Endochondral ossification

• Embryonic mesenchyme differentiates to cartilage – Chondrocytes– Perichondrium

• “Cartilage model” is starting point for endochondral ossification– (endo- = within, chondr- = cartilage)


Endochondral ossification

• Perichondrium becomes periosteum• Mesenchyme cells become osteoblasts

– Form primary ossification center

• Cartilage under bone collar calcifies & dies


Endochondral ossification• Invasion of nutrient blood vessel,• Continued deterioration of cartilage,• Formation of spongy bone


Endochondral ossification• Primary ossification

center grows, elongates,• Formation of marrow

cavity,• Formation of secondary

ossification centers at ends,

• Ossification of epiphyses.


Postnatal bone growth

• Growth in length at epiphyseal plates– Growth of cartilage

– Bone tissue “races” to keep up

• Growth in width at periosteum– Dismantling and

remodeling


Parts of a long bone

Bone cells


• Osteoprogenitor cells• Osteoblasts

– Bone forming cells– Lay down new bone

matrix (osteoid)

• Osteocytes– Mature bone cells– Isolated in lacunae

• Osteoclasts– Dismantle old bone

matrix– Release Ca2+ and

phosphate


Remodeling

• Normal continuous process– Osteoclasts dismantle old matrix– Osteoblasts rebuild bone matrix

• Allows– Maintenance of bone tissue– Change in shape with age & weight– Reinforcing of parts subject to stress & strain


Remodeling & Ca2+

• Depends on– Homeostasis of Ca2+

and phosphate

– Low Ca2+

• Parathyroid hormone (PTH) stimulates osteoclast activity

• Calcitriol & Vitamin D stimulate absorption of Ca2+ from intestine.


Remodeling & Ca2+

• Depends on– Homeostasis of Ca2+

and phosphate

– High Ca2+

• Calcitonin stimulates deposition of Ca2+ into bone tissue.

• Excess Ca2+ excreted.


Fracture repair

• Fracture hematoma– At time of break blood

vessels rupture, clot forms

– Macrophages, osteoclasts clean up

• Internal and external fibrocartilaginous callus– Fibroblasts & osteoblasts

enter site and lay down collagen fibers & cartilage matrix.


Fracture repair

• Bony callus– Osteoblasts lay down

spongy bone trabeculae

– Join broken ends

• Remodeling– Osteoblasts continue

forming bone

– Compact bone replaces spongy bone

19 sept. 2012bone_tissue.ppt1. 19 sept. 2012bone_tissue.ppt2 bones and skeletal tissues skeletal...

Documents

formation of bone

bone collar

bone weight slide

formation of spongy

outer surface of bone

cartilage slide

connective tissue cells

red slide