Bone Physiology CIS 9/20

Question 1

see the sheets that have been made

Answer 1

see sheets

Question 2

PTH

Answer 2

secreted when Ca is low in serum. results in stimulation of bone calcium resorption from bone, kidney reabsorption of calcium, decrease in phosphate reabsorption in kidneys, increase in Vitamin D activated

Question 3

1,25 (OH)2 - Vitamin D

Answer 3

Activated form of vitamin D

• results in gut calcium absorption
• phosphate reabsorption
• kidney tubule calcium reabsorption
• bone calcium reabsorption

Question 4

hypocalcemia

Answer 4

decreased calcium levels, decreases the sodium voltage threshold, which results in hyperexcitability and spontaneous muscle contraction –> tetany

Question 5

hypercalcemia

Answer 5

increased calcium levels, results in increased sodium voltage threshold, causing NS depression and slow reflex responses

Question 6

osteon

Answer 6

structural unit of the bone

Question 7

lacunae

Answer 7

irregular plates on trabecular bone where bone resportption has occured (contain osteocytes)

Question 8

lamellar bone

Answer 8

layers of organized bone

Question 9

osteoid

Answer 9

organic matrix of bone (laid down by osteoblasts)

Question 10

increased bone formation due to which hormones….

Answer 10

growth hormone, thyroid, insulin, gonadal hormones

Question 11

glucocorticoids

Answer 11

suppress calcium gut absorption by depleting osteoblasts –> suppresses bone formation

Question 12

Plekho 1

Answer 12

Pleckho1 is responsible for degradation of cofactors for osteoblastic activity. inhibition of Pleckho1 will result in increased bone density. Findings support increased bone density in a mouse model with Pleckho1 siRNA treatment. A novel finding in this article was the uncoupling of bone resorption and bone formation.

Question 13

Sclerostin

Answer 13

The normal function of sclerostin is a reduction in osteoblast activity. By inhibiting sclerostin action (blocking antibody) bone formation can potentially be increased.

Question 14

T score

Answer 14

low T score is indicative of osteoporosis (less than -2.5)

Question 15

urine N-telopeptide

Answer 15

• marker of collagen degredation

- result of increased osteoporosis

Question 16

alkaline phosphatase

Answer 16

• linked with bond formation

- seen high in children and in those with Paget’s disease

Question 17

How do osteoblasts work along with osteoclasts?

Answer 17

• Low Calcium levels results in release of PTH. PTH activates osteblasts which secrete MCSF and RankL/IL6. MCSF recruits osteoclasts. Osteoclasts are activated by RankL?IL-6 and the reabsorption of bone by osteoclasts , which is followed by the osteoblasts laying down new bone. This results in an increase in plasma calcium levels
• decreased RankL is seen in osteopetrosis
• increased RankL is seen in osteoporosis

Question 18

secondary causes of osteoporosis

Answer 18

• vitamin D deficiency
• increased PTH
• renal failure
• glucocorticoid excess
• hypogonadism
• increased thyroid hormone
• idiopathic hypercalcemia

Question 19

OPG

Answer 19

inhibits RankL/IL6 - and stops osteoclast action

Question 20

FGF23

Answer 20

• phosphate regulation at kidney level

- increase in FGF23 results in decreased Vitamin D and decreased Phosphate levels

Question 21

bisphosphates

Answer 21

• inhibit bone resorption – could lead to hypocalcemia, but is used to treat osteoporosis
• Prolia drug has a similar affect, but instead inhibits the binding of RankL/Rank and IL6R/IL6

Question 22

Osteoporosis

Answer 22

decreased bone density

Question 23

Osteomalacia/Rickets

Answer 23

disordered bone mineralization (due to decrease in vitamin D) –> decreased bone density/brittle bones

Question 24

Paget’s Disease

Answer 24

hyperactive bone remodelling by osteoblasts

Question 25

Osteogenesis Imperfecta (OI)

Answer 25

brittle bone disease: due to mutations in collagen

• Type I: decreased amount of collage, with normal structure due to inherited missing allele
• Type II: (most severe) - due to a point mutation in colagen resulting in abnormal collagen structure

Question 26

osteopetrosis

Answer 26

defective osteoclasts, results in increased bone density and disorganized bone structure