Skeletal System and Bone Production

Physical function of bone

support, movement, protection

Metabolic function of bone

blood cell formation, stores Calcium salts and lipids (adipose)

Hematopoiesis

blood cell formation

Epiphysis

Ends of long bone

• spongy bone

Diaphysis

middle section of long bone

• contains medullary cavity

• compact/dense bone

Cell of bone (osseous) tissue

specialized cells dispersed in a hardened EXTRAcellular matrix

Extracellular Matrix of bone

1/3 collagen fibers (flexibility), 2/3 calcium salts (hardness), ground subtance

Hydroxyapatite crystals

interaction of calcium and phosphate to for crystals

Journey of bone cells

Osteoprogentitor→osteoblast→osteocyte

Osteoprogenitor cell

stem cells that divide to create osteoblasts

Osteoblast

immature bone cells

osteocyte

mature bone cells, maintains bone matrix

osteoclast

immune cells that break down bone matrix

function of compact (dense) bone

protection, support, resist stress

Matrix of compact bone

osteon (haversian system)- cylindrical unit of concentric circles of lamellae and osteocytes in lacunae

Haversian canal- center canal of every osteon from blood vessels

Preforation canal- transverse blood vessel canals connecting to haversian canals

function of spongy bone

support, storage of marrow

Matrix of spongy bone

open network

interconnecting bundles of bone (trabeculae)

trabeculae are thin with laellae and osteocytes

red bone marrow

Red bone marrow

spongy bone

• hematopoiesis

• interior of flat bones/epiphysis of long bones/childs medullary cavity

• surrounds trabeculae

yellow bone marrow

long bone

• adipocytes (fat storage)

• medullary cavity of long bone

• begins as red, turns to yellow by adult

Periosteum

two outer layers that cover bone

inner: osteoblasts/osteoprogenitors

outer: fibrous membrane/firbroblasts

Endostium

incomplete interior covering, remodeling

covers trabeculae/haversian canals

epithelial/osteoprogenitor/osteoclast

Types of bone formation

Intramembranous ossification

Endochondral ossification

osteoid→mineralized

initially woven bone around blood vessels

Intramembranous bones

skull/clavicle

formed from mesenchyme

early fontanels separate bones of skull

Intramembranous ossification

1. Mesenchymal cells cluster (osteoblasts) around osteocytes

2. osteocytes differentiate and spicules project out

3. rate acclerates because blood vessels form

4. woven bone forms (disorganized)

5. organized bone and periosteum forms

Endochondral ossification

1. Formation of hyaline cartilage model (producted by chondroblasts)

2. Formation of bony collar (blood vessels grow around cartilage, outer ring differentiates into osteoblasts (bone collar)

3. Vascular invasion (blood vessels invade center/primary ossification center forms)

4. Elongation (blood vessels invade epiphysis generating secondary ossification centers/growth plates from)

5. Epiphyseal Plate ossification (post puberty groth plates close forming epiphyseal line)

Bone growth at growth plate (layers)

1. Reserve Zone - non-proliferative chondroblasts

2. Zone of Proliferation - rapid mitosis of chondroblasts

3. Zone of Hypertrophy - chondroblasts mature and enlarge

4. Zone of Calcification - dealth of chondrocytes/ calcificaton of matriz

Osteoblasts invade deposite bone matrix on calcified cartiladge

Bone Remodeling

100% per year

partially replaces the matrix

uses osteoblasts, osteoclasts, osteocytes

Vitamins that affect bone growth

Vitamin C - collagen synthesis in osteoblasts

Vitamin D - promotes calcium and phosphate from diet

Hormones

Parathyroid hormone - not enough calcium in blood/stimulates osteoclasts

Calcitonin - too much calcium in blood/inhibiting osteoclasts

Growth - stimulates growth and division

Thyroid - stimulates cell metabolism and osteoblast activity

Sex hormones

Androgens/Estrogens -