Endocrine Control of Bone Health

Question 1

Define each of the following:
diaphysis
epiphysis
periosteum
endosteum

Answer 1

Diaphysis: shaft of bone
Epiphysis: end of bone
Periosteum: covers outside of compact bone
Endosteum: inside of bone

Question 2

What % of bone is organic and what does this include?

Answer 2

35% of bone is organic, mostly osteoid matrix (collagen and calcium binding proteins) and bone cells

Question 3

What is the benefit of collagen in osteoid?

Answer 3

Provides flexibility and tensile strength to bone

Question 4

What % of bone is inorganic and what does this include?

Answer 4

65% inorganic, made of mineral salts, calcium phosphate and other minerals

Question 5

What do inorganic minerals in bone privde?

Answer 5

bone hardness

Question 6

Differentiate between the two types of bone ossification.

Answer 6

Intramembranous ossification where bone is created from fibrous membranes, skill, mandible and clavicle made this way
Endochondral ossification where bone replaces hyaline cartilage, most bones made this way

Question 7

List the 5 main steps of endochondral ossification.

Answer 7

1) bone collar forms around diaphysis of cartilage
2) cartilage calcifies in centre of diaphysis
3) periosteal bud invades cavities within diaphysis calcification
4) diaphysis elongates, medullary cavity forms, secondary ossification centres appear in epiphyses
5) epiphyses ossify

Question 8

Where is the only place cartilage is left after endochondral ossification and what does this allow?

Answer 8

between first and second ossification centres, allows elongation to occur

Question 9

Formation of bone and remodelling is strongly influenced by which 2 molecules?

Answer 9

vitamin D and PTH

Question 10

describe the role of: osteoblast, osteoclast and osteocyte

Answer 10

osteoblast- builds bone by secreting osteoid
osteoclasts- clear away bone to release calcium and other minerals
osteocyte- mature osteoblast that resides in bone matrix for many years monitoring and modifying bone properties

Question 11

Describe the 4 main steps of intramembranous ossification

Answer 11

1) ossification centres develop in fibrous connective tissue membrane
2) osteoid secreted and calcifies
3) immature spongy bone and periosteum form
4) compact bone replaces immature spongy bone, just deep to periosteum, red marrow develops

Question 12

What % skeleton replaced /year?

Answer 12

10%

Question 13

How often is spongy bone replaced compared to compact?

Answer 13

spongy bone every 3 years, compact bone every 10 years

Question 14

List the two main reasons for bone remodelling.

Answer 14

1) longer calcium stays in bone, more brittle it becomes, constant turnover=strong bone
2) bones are major calcium store in body, calcium released when required

Question 15

Explain PTH relationship with bone remodelling

Answer 15

Decreased calcium levels in blood cause increase in PTH which stimulates release of RANK-L from osteoblasts and decrease release of osteoprotegrin, this triggers formation of new osteoclasts and increases activity of existing = resorbs bone and releases calcium into blood

Question 16

Explain Vitamin D relationship to bone remodelling.

Answer 16

Acts on small intestine to increase calcium absorption, decreases kidney excretion of calcium, stimulates RANK-L release and decreases synthesis of osetoprotegerin

Question 17

Explain relationship between PTH and vitamin D

Answer 17

PTH helps produce vitamin D

Question 18

Why do osteocytes secrete osetoprotegerin?

Answer 18

To bind to RANK-L to inhibit activation of osetoclasts

Question 19

Which hormones increase osteoprotegerin?

Answer 19

TH, estrogen, GH

Question 20

Explain 4 main steps of repair of a fracture

Answer 20

1) haematoma forms
2) fibrocartilaginous callus forms
3) bony callus forms
4) bone remodelling occurs

Question 21

Define osteomalacia

Answer 21

Group of bone disorders where osteoid is produced but minerals not stored adequately

Question 22

Describe Rickets

Answer 22

Rickets is childhood form of osteomalacia leading to poor mineralisation in growth plates and bowed legs, caused by insufficient calcium or vitamin D

Question 23

Describe osteoporosis

Answer 23

Group of disorders where bone resorption outpaces bone deposition, matrix remains normal but bone mass declines

Question 24

Why is osteoporosis associated with postmenopausal women?

Answer 24

Estrogen promotes osteoblast function therefore after menopause estrogen levels drop decreasing function of osteoblasts. Additionally, estrogen increases OPG levels therefore without this increase there is more free RANK-L to activate osteoclasts

Question 25

Which hormones stimulate RANK-L?

Answer 25

IGF, PTH, vitamin D, glucocorticoids