• support
• prtect
• movements
• store & release of calcium & phosphorus
• blood cell formation
• store triglycerides

§femur, humerus, phalanges, etc.

• diaphysis- shaft/body (hollow & contains mostly yellow marrow)
• epiphyses- ends (contains red marrow in proxial epiphysis of humerus and femur
• metaphyses- where the epiphyses and diaphysis join (epiphyseal plate & epiphyseal line)

Bone Structure:

epiphyseal growth plate

in adolescents- hyaline cartilage (epiphyseal line), cartilage is replaced by calcified bone

Bone Structure:

medullary cavity

Bone Structure:

endosteum

a membrane, usually a single layer of cells that lines the medullary (marrow) cavity, central and volkman's canals, and covers trabeculae of spongy bone

composed of osteoclasts, osteoblasts, and osteoprogenitor cells

Tissues of the Skeletal System:

periosteum

dense irregular connective tissue

• contains osteoblasts
• vascular
• fracture repair and serves as an attachment point

Tissues of the Skeletal System:

Articular cartilage

hyaline cartilage

• found where the bone forms an articular surface
• prevents friction

Bone Cells:

osteoprogenitor

osteogenic cells

• derived from mesenchyme
• develops into osteoblasts
• located in inner periosteum, edosteum, Volksman's and central canals

Bone Cells:

Osteoblasts

building cells

*secrete collagen fibers and other organic components

Bone Cell:

osteocytes

mature osteoblasts (maintenance)

Located in lucuna

Bone Cell:

Osteoclasts

breakdown cells

• develop from monocytes
• release digest collagen and dissolves Ca2+ salts

Tissue of the Skeletal System:

compact bone

protection and support

• forms diaphysis of long bone and the external layer of all bones
• collagen fibers produced by osteoblasts
• osteoblasts become osteocytes

Tissue of the Skeletal System:

Spongy bone

lightweight and provides tissue support

• forms epiphysis and the internal cavity of long bones
• has latticework of thin plates called trabeculae

Tissue of the Skeletal System:

Cartilage

poorly vascularized C.T.

• hyaline
• fibrocartilage or elastic cartilage

Tissue of the Skeletal System:

perichondrium

dense irregular C.T. 

• Chondrocytes- cells that form cartilage
• many bones ar formed from cartilage

Tissue of the Skeletal System:

other important tissues

Endothelium-forms capallary walls

nerves

Red marrow- hematopoiesis

yellow marrow- fat storage

Histology of Bone Tissue:

Osteons

concentric lamellae

interstitial lamellae

Osteons are in compact bone and are also harcersian systems formed form concentric lamellae

Interstitial lamellae are between osteons, left over fragments of older osteons

Histology of Bone Tissue:

Outer circumferential lamellae

Inner circumferential lamellae

• encurcle the bone beneath the periosteum
• encircle the medullary cavity

Histology of Bone Tissue:

lacunae

Canaliculi

• small spaces between the lamellae which hous osteocytes
• small channels filled with extracellular fluid connecting the lacunae

Histology of Bone Tissue:

Central Canal

Perforating (Volkmann's) canal

• where blood and lymphatic vessels are in the osteons
• allow transit of these vessels to the outer cortex of the bone

Histology of Bone Tissue:

spongy bone

compact bone

• lacks osteons, lamellae are in thin columns called trabecule

trabecule support and protect the red bone marrow and re oriented along lines of stress

Hematopoiesis- blood cell production

• lacunae contain osteocytes that nourish the mature bone tissue from the blood circulating through the trabeculae

• Periosteal arteries and veins supply the periosteun and compact bone
• nerves accompany the blood vessels

Bone Formation:

Ossification

process of froming new bone, 4 situations:

• formation of bone in an embryo
• growth of bones until adulthood
• remodeling of bone
• repair of fractures

Bone Formation:

embryo

starts at 6 weeks

skeleton is composed of fibrous membrane and hyaline cartilage is shape of bones

formed by mesenchymal cells

Bone Formation:

Intra-membranous ossification

 Endochondral ossification

• produces spongy bone; may be remodeled to form compact bone
• process whereby cartilage is replaced by bone; forms compact and spongy

Bone Growth:

4 zones of cells

•zone of resting (quiescent) cartilage - epiphyseal side (no mitosis)

Bone Growth:

Growth in diameter

• Osteons are constructed on the outside of the bone
• Osteoblasts from the periosteum add new bone tissue, enclosing a blood vessel running though the periosteum
• osteoblasts in the endosteum continue to make more bone tissue in concentric rings, lamellae, resulting in a new osteon
• osteoclasts break down the medullary endosteum and destroy bone lining of the marrow cavity

a balance must exist between the actions of osteoclasts and osteoblasts

bones could weaken or become to soft (rickets-children, osteomalacia-adults)

Bone growth and remodeling:

vitamins

A-osteoblAst

C-Collagen

D- absorption

K & B12- synthesis of bone protein

**D-BACK

Bone growth and remodeling:

hormones

Human Growth Hormone (HGh) & IGFs

stimulates osteoblasts for normal bone growth, cell division,muscle growth, loss of fat, protein synthesis, increase in glucose output in the liver

Thyroid hormone- promotes bone growth by stimulating osteoblasts and protein synthesis

Sex hormones- causes growth spurt, widening of female pelvis, closing of epiphyseal plates

Parathyroid hormone (PTH) & Calcitonin- help balance levels of calcium and phosphorus

porous bones

• resorption outpaces bone deposition
• depletion of calcium
• caused by decrease of sex hormones w/ advancing age

bacterial infection in bone

• bacteria reaches bone by blood, fractures, sinus infection, tooth abscess

most common

• myeloid= marrow
• startin bone or start after metastasis from breast, prostate cancer

Fracture- any break in a bone

Open- thtough the skin

impact- distal end is shoved into proximal part

comminuted- bone shattered

greenstick- bend (half broken)

Patholoical fracture- chronic disease, trauma

Stress fracture- repeaated activities

depressed- broken portion is pressed inward

spiral- twisted

epiphyseal- seperates from diaphysis

Colles- distal radius

Potts- distal fibula

1. hematoma- blood vessels breaking in the periosteum and osteons
2. phagocytes remove cellular debris and fibroblasts deposit collagen to form fibrocartilaginous
3. osteoblasts form a bony callus of spongy bone to replace the firocartilage
4. remodeling- spongy bone is replaces by compact bone (if needed)