Bone Development and Healing - smittyworld.comsmittyworld.com/userfiles/Bone Develoopment.pdf7 Bone Development.notebook February 05, 2015 Bone Development and Healing human bones

7 Bone Development.notebook February 05, 2015

Bone Development and Healinghuman bones develop at different rates and times throughout the developmental stages of growth

• cells that promote bone formation present after 3 weeks of development• these cells are formed from mesoderm = all the body's connective tissues and muscle• when embryonic tissues become recognizable bone = ossification

Ossification occurs 2 ways:1) endochondral ossification

bone formation that begins within a cartilage endo chondral

• after the 5th week of development • specialized mesoderm cells form concentrations of cartilage where bone will form• these concentrations grow, and develop into pegs of cartilage that resemble smaller versions of bones• as development continues, the pegs are restructured and fill with a type of calcium = calcification• the first formation and shaping of bone occurs by fibroblasts• then osteoblasts and osteoclasts (bone forming cells) move in

osteoblasts build bone tissueosteoclasts break down bone and cartilage

together they sculpt forming bones


diet greatly affects the function of osteoblasts & osteoclasts • calcium and vitamin D stimulate bone growth and maintenance

parts of the endocrine system produce chemicals that also regulate the rate of bone growth


3 distinct events during endochondral ossificationa) primary ossification• osteoclasts carve a cavity in the center of the cartilage = diaphysis• blood vessels begin to grow into the bone forming in the cavity =

nutrients for bone growth and maintenance• osteoblasts enter the cavity and begin replacing the cartilage with bone tissuecompact bone first, then compact bone is converted into spongy bone as the cavity enlarges

primary ossification and bone collar formation continue until the bone is mature = late teens, early 20s

rate of long bone growth is a factor in overall body weight

b) bone collar formationat the same time, osteocytes in the periosteum produce the bone collar a dense,sheetlike layer of bone on the surface of the diaphysis

*both of these events widen and elongate the bone*remember, bone elongation occurs in the epiphyseal plate



c) secondary ossification• late in fetal development, sometimes right before birth• osteoclasts form a small cavity in the epiphysis• blood vessels and osteoblasts enter the cavity and begin building bone

out of cartilage• much slower rate than primary ossification• doesn't form a full bone collar in some cases is

deposited over the areas forming the articular surfaceshyaline cartilage

bone thickening and sculpting can continue during an individual's life

osteoblasts eventually develop into osteocytes in mature bone tissuethe osteocytes are more involved in maintenance than formation

20 ossification continues through adolescence stops when cartilage growth slows stops late 20s this is when the epiphyseal line forms



2) intramembranous (direct) ossification• simpler than endochondral• doesn't require cartilage• is the replacement of sheetlike fibrous connective tissue

membranes by bone tissue• 1st the membranes are laid down where the bone will form• osteoblasts move into the membranes and deposit spongy bone

matrix• blood vessels develop in the matrix and osteoclasts assist in

further bone growth• a thin cap of dense bone is deposited on the surface of most

intramembranous bones osteoblasts in the periosteum

abnormally formed or missing connective tissue membranes can cause skeletal birth defects

intramembranous development can be found in the skull of a baby's skull

fontanelles (soft spots) are large sutures in areas where flat bone has not completed intramembranous development

the skull fully ossifies in the teenage years


Bone Growth as a Result of Repairfractures are the more common type of bone damage =

bone is cracked or splintered due to physical injuryfractures are classified based on the severity of the break or angle of the break

simple fracture• least severe• crack in the bone • can be so small, they are not noticeable• can be large enough to involve bleeding, pain, and

swelling

other bone fractures

greenstick fracture• common in children• one side of bone is frayed from the fracture, the other side is twisted


reactive stage fracture & granularreparative stage callus & lamellar bonerestorative stage normal contour

fracture granularcalluslamellar bonenormal contourfracture body's reaction to the injury• bleeding• tissue damage• blood clotting to begin healing within first hours or days of damage

Stages of Bone Repair

granular step white blood cells enter the damaged area• new blood vessels form• bone tissue takes on a granular appearance = name WBCs are digesting and breaking down damaged tissue and clotted blood


callus • mass of tissue• beginning of repair• osteoblasts secrete new bone tissueduration can be for weeks to months

lamellar bone layers of new bone continue to be laid down forming new bone structure

normal contour osteoclast attempt to sculpt the new bone tissue into its original shape


small fractures are usually completely repaired

medical professionals can detect past fracturespast fractures = bone density is different in xrays

fractures demand • higher metabolic rate• increase uptake of calcium & proteins

undernutrition/malnutrition• can slow healing process• can stop healing process

bone healing can be monitored by• measure osteoblast activity• test for alkaline phosphatase• measure for waste byproducts of bone rebuildingbone healing can also be used to identify bone diseases

large fractures seldom are completely healed

bones never return to their original condition


Hyaline cartilage is the most widespread and is the type that makes up the embryonic skeleton. It persists in human adults at the ends of bones in freemoving joints as articular cartilage, at the ends of the ribs, and in the nose, larynx, trachea, and bronchi. It is a glossy bluewhite in appearance and very resilient.

return


Documents

Bone Development and Healing - smittyworld.comsmittyworld.com/userfiles/Bone Develoopment.pdf7 Bone Development.notebook February 05, 2015 Bone Development and Healing human bones