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Tissues Of The Body > Ossification and Bone Diseases > Flashcards

Ossification and Bone Diseases Flashcards

1
Q

Which type of bones develop by endochondral ossification?

A

Long bones

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2
Q

What are growth plates made from?

A

Hyaline cartilage

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3
Q

What happens to the epiphyseal plate of long bones after the cessation of growth?

A

They disappear.

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4
Q

What is endochondral ossification?

A

The replacement of a pre-existing hyaline cartilage template by bone. This is the way most of the bones in the body develop.

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5
Q

What is intramembranous ossification?

A

Takes place within condensations of mesenchymal tissue and not by replacement of a pre-existing hyaline cartilage template.
Process also contributes to thickening (widening) of long bone.

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6
Q

Which bones develop by intramembranous ossification? Give examples.

A

Flat bones e.g. Skull bones, maxilla, mandible, pelvis, lateral end of clavicle

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7
Q

How does intramembranous ossification happen?

A

Mesenchymal cells become osteoprogenitor cells which become osteoblasts and lay down osteoids in an extracellular matrix made up of type 1 collagen.
The osteoid mineralises to form rudimentary bone tissue spicules, which are surrounded by osteoblasts and contain osteocytes.
Spicules join to form trabeculae, which merge to form woven bone, which is finally replaced by the lamellae of mature compact bone.

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8
Q

What is osteogenesis imperfecta? What mutation is it caused by? What areas of the body does it affect?

A

An autosomal dominant group (I-IV) of heritable disorders of connective tissue.
Caused by mutations in the gene for type I collagen.
Affects the skeleton, joints, ears, ligaments, teeth, sclerae and skin.

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9
Q

Why is osteogenesis imperfecta of medicolegal importance?

A

Because of the possible confusion which multiple fractures caused by deliberate injury.

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10
Q

Where is growth hormone (GH) synthesised? Where is it stored?

A

In the anterior pituitary.

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11
Q

What is the effect of excessive GH and insufficient GH before puberty?

A

Excessive GH - gigantism through the promotion of epiphyseal growth plate activity.
Insufficient GH - can affect epiphyseal cartilage and cause pituitary dwarfism.

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12
Q

What is the effect of excessive GH in an adult?

A

Excessive GH may cause increase in bone width by promoting periosteal growth - acromegaly

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13
Q

Why does excessive GH in an adult not cause gigantism?

A

Because there are no longer any epiphyseal plates

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14
Q

What do sex hormones influence in bone development?

A

The development of ossification centres

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15
Q

What is the effect of excessive sex hormones on bone?

A

Precocious sexual maturity retards bone growth because of premature closure (fusion) of epiphyses

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16
Q

What is the effect of insufficient sex hormone?

A

Epiphyseal plates may persist later into life than they normally would, leading to prolonged bone growth and tall stature

17
Q

What is the effect of untreated thyroid hormone deficiency in an infant?

A

Permanent neurological and intellectual damage (cretinism) and a number of others abnormalities, one of which is short stature.

18
Q

What is osteoporosis?

A

A metabolic bone disease in which mineralised bone is decreased in mass and no longer provides adequate mechanical support.
Osteoporosis associated with aging results from incomplete filling of osteoclast resorption bays

19
Q

When does bone mass peak and decline?

A

Peaks in between 25-35 years and declines from 5th/6th decade

20
Q

What is type 1 osteoporosis?

A

Occurs in postmenopausal women. Due to an increase in osteoclast number, a result of oestrogen withdrawal.

21
Q

What is type 2 osteoporosis?

A

Occurs in elderly persons of both sexes (senile osteoporosis). Generally occurs after age 70 and reflects attenuated osteoblast function.

22
Q

What are risk factors associated with osteoporosis?

A

Genetic - peak bone mass higher in black people
Insufficient calcium intake
Insufficient calcium absorption and vitamin D
Exercise - immobilisation of bone
Cigarette smoking

23
Q

What is achondroplasia? What is it caused by?

A

One of the most common forms of short limb dwarfism.

Caused by an autosomal dominant point mutation in the fibroblast growth factor receptor-3 gene (FGFR3)

24
Q

What does the point mutation in the FGFR3 result in?

A

Decreased endochondral ossification
Inhibited proliferation of chondrocytes in growth plate cartilage
Decreased cellular hypertrophy
Decreased cartilage matrix production

25
Q

What is the importance of Vitamin D in normal bone development?

A

Some vitamin D is dietary, most is synthesised in the skin by action of UV light. Both types undergo hydroxylation in the liver.
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