12. Ossificaiton and Bone Disease Flashcards Preview

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Talk through the process of endochondral ossification in long bone development.

There is an initial hyaline cartilage model.
A collar of periosteal bone starts forming at the sides of the long bone. The central cartilage calcifies and nutrient arteries penetrate and supply bone-depositing osteogenic cells. The medulla becomes cancellous bone and cartilage forms epiphyseal growth plates. Epiphyses develop secondary centres of ossification. Epiphyses ossify and growth plates continue to move apart and lengthen the bone. The epiphyseal growth plates are replaced by bone but hyaline cartilage at articular joints persists.


Where does intramembranous ossification take place?

Within condensations of mesenchymal tissue.


What is osteogenesis imperfecta?

An autosomal dominant groups of heritable disorder of connective tissue caused by mutations in the gene for type I collagen.


What are the four types of osteogenesis imperfecta?

Type I - initially lots of severe fractures but decrease in frequency and severity as child grows. Bones are thin, delicate and curved. Sclerae are blue and thin. Loss of hearing due to fusion of auditory ossicles.
Type II - lethal perinatal disease. Almost all bones fracture in childbirth.
Type III - progressive deforming disease. Many bone fracture, growth retardation and severe skeletal development.
Type IV - like type I but with normal sclerae. Patients treated with orthopaedic devices to prevent dwarfing.


Why is osteogenesis imperfecta of medicolegal importance?

Because there could be confusion with the cause of the multiple fractures, the parents might be thought to be abusive.


Where is growth hormone synthesised and stored?

The anterior pituitary.


What can excessive GH cause before puberty?

Gigantism from promotion of epiphyseal growth plate activity.


What can insufficient GH cause before puberty?

Pituitary dwarfism as epiphyseal cartilage is affected.


What can excessive GH cause in an adult?

Increase in bone width by promoting periosteal growth, which can lead to acromegaly.


How do sex hormones affect bones?

Influences development of ossification centres. They induce secondary sexual characteristics and give rise to pubertal growth spurts.


What can precocious sexual maturity lead to?

Bone growth retardation because of premature closure of epiphyses.


What can sex hormone deficiency lead to?

Tall stature due to epiphyseal plates closing later in life so there is prolonged bone growth.


What can untreated hypothyroidism in new borns lead to?

Cretinism and short stature.


What is osteoporosis?

A metabolic bone disease where mineralised bone decreases in mass so it no longer provides adequate mechanical support.


What is type I osteoporosis caused by and who does it affect?

Caused by an increase in osteoclast number from oestrogen withdrawal. It affects postmenopausal women.


Who does type II osteoporosis affect and what is it caused by?

In elderly, it's from attenuated osteoblasts function.


What are five risk factors with osteoporosis?

Genetic, insufficient calcium intake, insufficient calcium absorption and vitamin D, exercise and cigarette smoking.


What is achondroplasia?

Short limb dwarfism caused by an autosomal dominant point mutation in the fibroblast grow factor receptor-3 gene.


What is endochondral ossification?

The replacement of pre-existing hyaline cartilage template by bone.


What is achondroplasia caused by?

Gain of function of the FGFR3 gene. This results in decreased endochondral ossification, inhibited proliferation of chondrocytes in growth plate cartilage, decrease cellular hypertrophy and decreased cartilage matrix production.


What is the importance of vitamin D?

Increases calcium abortion by the small bowel and promotes mineralisation of the bone.


What is Rickets?

A childhood disease where the bones don't harden because of a deficiency of vitamin D. Bones becomes soft and malformed.


What is osteomalacia?

The adult counterpart to Rickets. It's cause by a significant calcium deficiency or lack of vitamin D. It causes bone pain, back ache and muscle weakness.