4 Intramembranous Bones In The Fetus The flat bones of the skull are INTRAMEMBRANOUS BONES.During their development, unspecialized connective tissue appears at the sites of future bones.Dense blood vessels form and supply the connective tissue with blood.Eventually, through a process called intramembranous ossification, this connective tissue forms flat bone.
5 Endochondral Bones In The Fetus Most bones of the skeleton are ENDOCHONDRAL BONES.They develop from masses of hyaline cartilage shaped like future bony structures.These cartilaginous models grow rapidly for a time and then begin to change extensively.Eventually, through a process called endochondral ossification, this hyaline cartilage forms endochondral bones.
6 Endochondral Bone Development Major Stages (a-d fetal), (e child), (f adult)
7 Fetal StageIn the region known as the primary ossification center, bony tissue begins to replace hyaline cartilage.The epiphyses remain cartilaginous and continue to grow into secondary ossification centers.
8 Child StageHere, in the child stage of long bone, we see the formation of the epiphyseal plates or disks.These plates lie between the primary and secondary ossification centers of the long bone.Long bone continues to lengthen while the epiphyseal plates are active.However, once the epiphyseal plates ossify, lengthening is no longer possible at that end of the bone.
9 Adult StageA developing bone thickens as compact bone just beneath the periosteum or outer layer of bone.The bone in the central regions of the epiphysis and diaphysis remains spongy, and hyaline cartilage on the end of epiphyses persists throughout life.
10 What Do Bones Need to Grow? Vitamin A supports bone developmentVitamin C strengthens boneVitamin D supports bone structureBones, like muscles, need physical stress to break down and cause the bone to regenerate healthier cells
11 Vitamins Vitamin A Vitamin C Vitamin D Necessary for osteoblast and osteoclastDeficiency may retard bone developmentVitamin CRequired for collagen synthesisDeficiency results in slender, fragile bonesVitamin DNecessary for calcium absorption
12 Hormones Growth Hormone Stimulates division of cartilage cells Pituitary dwarfism- bones fail to develop normally and child is very short. This is due to lack of growth hormone.Pituitary gigantism- excess growth hormone is released, height may exceed 8 ft.Acromegaly- In adults, excess growth hormone causes enlarged hands, feet, and jaw.
13 Hormones (cont’d) Sex Hormones In males testosterone, in females estrogenCause long bones to grow considerably.Become abundant at pubertyEstrogen typically has a stronger effect on epiphyseal plates which is why females reach their maximum growth earlier than males.
14 Hormones (cont’d) Thyroid Hormone Stimulates replacement of cartilage with bone tissueIncreases cellular metabolismStimulates osteoblast activity
15 Male vs Female GrowthFemales tend to hit puberty earlier than boys. This is why girls are usually taller than boys in elementary school. Girls usually stop growing at the age of 17.Males develop longer and hit puberty at an older age. This is why men tend to be taller than women in adulthood. Men usually stop growing by the age of 18 but can grow up to the age of 25.As our body ages, both sexes decrease in heighth after about age thirty.
16 Life-Span Bone Growth Puberty age 12 Puberty age 10 Age 30 Age 30 Male Skeletor Female Skeletor