BONE METABOLISM AND METABOLIC BONE DISEASE

Question 1

what are the 4 main functions of bone?

Answer 1

mechanical support
protection of vital organs
haematopoiesis
calcium storage

Question 2

what are the 2 compartments of bone?

Answer 2

a collagen matrix and organic cells (osteoblast, osteoclasts and osteocytes)

Question 3

outline bone remodelling?

Answer 3

Osteoclasts first excavate a cavity within the bone
After a few weeks, osteoblasts begin to produce osteoid and the osteoclasts enter programmed cell death
Within three months the newly formed osteoid is then mineralised, forming new bone

Question 4

at what age is bone mass at its peak?

Answer 4

around 30

Question 5

after 30 why do humans get a slow but steady loss of bone mass?

Answer 5

trabeculae become thinner and the bone becomes more porous

Question 6

describe what happens to bone mass when women reach menopause?

Answer 6

they rapidly lose bone mass in response to a reduction in oestrogen that decreases osteoblast and increases osteoclast activity

Question 7

how is most of calcium and phosphorous stored?

Answer 7

in the bones as hydroxyapatite crystals

Question 8

what promotes calcium absorption from the gut into the serum?

Answer 8

vitamin D

Question 9

what promotes calcium resorption in the kidneys?

Answer 9

parathyroid hormone

Question 10

what promotes gut absorption of phosphorous?

Answer 10

vitamin D

Question 11

what promotes excretion of phosphorous by the kidney?

Answer 11

Parathyroid hormone

Question 12

how do we get vitamin D?

Answer 12

diet and the action of sunlight on skin

Question 13

what is vitamin D3? what is vitamin D2?

Answer 13

cholecalciferol

ergocalciferol

Question 14

what is the inactive form of vitamin D called?

what is the active form of vitamin D called?

Answer 14

25-hydroxyvitamin D

1,25-hydroxyvitamin D

Question 15

how do we produce 1,25-hydroxyvitamin D?

Answer 15

vitamin D2 and D3 undergo hydroxylation in the liver to produce 25-hydroxyvitamin D which then undergoes further hydroxylation and activation in the kidneys (catalysed by PTH) to form 1,25-hydroxyvitamin D

Question 16

what catalyses the activation of vitamin D?

Answer 16

parathyroid hormone

Question 17

what is the aim of 1,25-hydroxyvitamin D?

Answer 17

to increase serum calcium and phosphate levels

Question 18

how does 1,25-hydroxyvitamin D increase serum calcium and phosphate levels?

Answer 18

Increase calcium and phosphate absorption from the intestine

Induces bone marrow monocytes to differentiate into osteoclasts to stimulate bone resorption

Targets the PCT in nephrons to stimulate the reabsorption of phosphate and calcium

Question 19

what inhibits the parathyroid gland?

Answer 19

1,25-hydroxyvitamin D

Question 20

where is parathyroid hormone secreted from?

Answer 20

the 4 parathyroid glands on the thyroid gland

Question 21

when does parathyroid hormone get secreted?

Answer 21

at low serum calcium levels

Question 22

how does parathyroid hormone increase calcium and phosphate serum levels?

Answer 22

Break down bone to release calcium and phosphate into the plasma

Stimulates cells in DCT in nephrons to reabsorb calcium
Targets 1 alpha hydroxylase which activates vitamin D (1,25 (OH)2 vitamin D3)

increased calcium & phosphate absorption from intestine, via 1,25 (OH)2 vitamin D3- =Indirect effect

Question 23

what does calcitonin do?

Answer 23

lowers serum calcium and phosphate levels

Question 24

where is calcitonin released from?

Answer 24

the parafollicular cells of the thyroid in response to high serum calcium levels

Question 25

what is the mechanism of calcitonin?

Answer 25

to reduce bone resorption by activating calcitonin receptors expressed by osteoclasts

Question 26

what expresses oestrogen receptors?

Answer 26

oestoblasts and osteoclasts

Question 27

how does oestrogen maintain bone mass?

Answer 27

it inhibits osteoclast formation and function- reduces bone resorption it lowers serum calcium and phosphate levels- increases bone levels of them

Question 28

what are androgens?

Answer 28

male sex hormones but are also present in females. e.g. testosterone

Question 29

how do androgens decrease bone resorption?

Answer 29

by inhibits osteoclasts

Question 30

what is the cause of osteoporosis?

Answer 30

excess osteoclast and reduced osteoblast activity causes trabecular bone becomes fragile and bone density is reduced, resulting in an increased risk of fracture

Question 31

what are risk factors for osteoporosis?

Answer 31

age, being female, early menopause, hyperthyroidism, glucocorticoid therapy, chronic diseases, low BMI, anorexia, family history of hip fractures, smoking, alcohol, low testosterone

Question 32

how can osteoporosis present?

Answer 32

Back pain, caused by a fractured or collapsed vertebra. Loss of height over time. A stooped posture. A bone that breaks much more easily than expected

Question 33

what is DEXA?

Answer 33

an X-ray that measures bone mineral density and bone loss- normally taken on hip, spine and wrist)

Question 34

what is osteopenia?

Answer 34

low bone mineral density but not at osteoporosis levels

Question 35

what is the treatment for osteoporosis?

Answer 35

minimise risk factors ; fall reduction; diet; weight-bearing exercise; calcium and vit D; bisphosphonates

Question 36

what are bisphosphonates? | what are the main side effects?

Answer 36

drugs that inhibit osteoclastic activity to prevent the loss of bone density- has GI side effects

Question 37

what is osteomalacia?

Answer 37

vitamin D deficiency in adults- causes a failure of bone mineralisation causing a structural change in the bone matrix

Question 38

what is rickets?

Answer 38

vitamin D deficiency in children- causes a failure of bone mineralisation causing a structural change in the bone matrix

Question 39

how many adults in the UK have a vitamin D deficiency?

Answer 39

50%

Question 40

causes of vitamin D deficiency?

Answer 40

inadequate diet, lack of sunlight, malabsorption, liver or kidney disease, drugs, calcium deficiency, rare genetic conditions

Question 41

how can we prevent osteomalacia?

Answer 41

dietary supplements sunlight exposure education

Question 42

how does osteomalacia present?

Answer 42

asymptomatic, bone and muscle pain, muscle weakness, paraesthesia, fractures and deformities

Question 43

how do we diagnose osteomalacia?

Answer 43

a blood test

Question 44

what is the treatment for osteomalacia?

Answer 44

vitamin D supplements