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Ch. 6 Skeletal System (6.3 Ossification & Appositional Growth…
Ch. 6 Skeletal System
6.3 Ossification & Appositional Growth
Ossification, replacing other tissue with bone
Intramembraneous Ossification
Osteoblast differentiate within embryonic or fetal fibrous tissue (flat bones of skull, mandible & clavicle)
Endochondral Ossification
From existing hyaline cartilage
Step 1
: chondrocytes enlarge & die
Step 2
: Blood vessels invade the perichondrium, inner ayer differentiate into osteoblast
Step 3
: primary ossification center forms, spongy bone fills shaft of bone
Step 4
: Osteoclast form marrow cavity & epiphyseal cartilage forms
Step 5
: Secondary ossification centers begin and left with spongy bone & articular cartilage
Appositional Bone Growth
Osteoblast in the periosteum deposit new bone on outer surface. Osteoclast erode the inner surface
Bone Growth and Body Proportions
Ossification of toes completed by age 11 pelvis and wrist by age 25 arms & legs 18W & 20 M
Requirements for normal bone growth Vitamin D3
Liver, kidneys, calcitriol adsorb calcium & phosphate ions form digestive tract prevents rickets (softening & bending of bones)
rate of bone growth is controlled by human growth hormone from the pituitary sex hormones from the glands, ossification of bones is completed by age 25, & cartilage of epiphyseal plate replaced by bone formed the epiphyseal line
cartilage cells are produced by mitosis on the epiphyseal side, and destroyed and replaced by bone on the diaphyseal ide.
2 types of ossification: intramembraneous & endochondral
Most bones of the skeleton formed in this manner
primary & secondary ossification bone development & growth, the skeleton is an embryo and composed f fibrous ct membranes loosely shaped like bones.
provides supporting structures of ossification to begin at about 6-7 weeks gestation, ossification begins & continues throughout adulthood
6.1 Skeletal Primary Function
Support storage
Calcium salts and fat (yellow marrow)
Blood cell production
RBC's & WBC;s (red marrow)
Protection
Rib & pelvic bones
Leverage
For movement
6-2 within the bone cellular endosteum lines the marrow cavity & other inner surfaces, active during bone growth & whenever repair or remodling is underway
macroscopic features of bone long & short bones, flat & irregular bones
supporting connective tissues that contains specialized cells & a matrix consisting of extracellular protein & a ground substance.
the distinctive texture of one results from the deposition of calcium salts within the matrix calcium phosphate accounts for two thirds of weight of bone.
microscopic features of bone: osteocytes, lacunae, lamelle, canaliculi
two types of tissue: compact & spongy bone
6.6
thoracis cage: includes ribs, sternum, thoracic, vertebrae, and costal cartilage
ribs: 12 pairs, 7 are true, 5 are false, and last 4 are floating
sternum: manubrium= upper portion
body middle vertical portion
xyphoid process= lower extension
typical vertebrae body: discoid shaped anterior region, vertebral arch: posterior region, pedicle= short bony
posterior projection, lamina: flattened plates that articulate posteriorly into the spinous process, vertebral foramen; opening between body ad vertebral arch through which the spinal cord passes, spinous process: midline posterior proection, transverse process: laterally from pedicle
6.2 Bone Shape & Structure
compact bone
osteon functional unit
concentric layers of lamellae that contain lacunae where osteocytes. All wrapped around a central canal
perforating canals go from one osteon to another with blood vessels and nerves
6.4 & 6.5
bone remodling and repair: process involves osteoclasts & blasts involves 2 hormones parathyroid which adds calcium & calcitonin which lowers calcium levels
materials needed for bone remodeling: calcium, phosphorus, magnesium, boron, manganese vitamins needed human growth hormone, sex hormones (estrogens and androgens) thyroid hormones (T3 & T4 TH and calcitonin
6.5 after metapause women began to lose bone mass more rapid, by age 70 bone loss between sexes is similar, osteoporosis: sever bone loss after 45 occurs 29% of women
6-1 the skeletal system has 5 primary functions: support, storage, blood cells production, protection, leverage
bones classified according to shape & structure