Week 1: Metabolic disorders of bone

Question 1

Where are calcium-sensing receptors located?

Answer 1

Throughout the body

PTH

Kidney

Brain

GI tract

Question 2

What is the function of the calcium-sensing receptors?

Answer 2

Senses the extracellular calcium concentration

Mediates effects on target tissues

Question 3

What is the effects of PTH on the kidney?

Answer 3

Increase calcium resorption

Increase the hydroxylation from 25OH cholecalciferol to 1,25 dihydroxyvitamin D

Question 4

What are the sources of vitamin D?

Answer 4

Sunlight (biggest source of vitamin D)

Diet

Supplement

Question 5

What is the normal levels of vitamin D?

Answer 5

400IU/day

Question 6

Describe the possible causes of high calcium and high PTH?

Answer 6

Primary hyperaparathyroidism

Question 7

Describe the possible causes of high calcium and low PTH?

Answer 7

Malignancy

Question 8

Describe the possible causes of low calcium and high PTH?

Answer 8

Secondary hyperparathyroidism

Vitamin D deficiency

Question 9

Describe the possible causes of low calcium and low PTH?

Answer 9

Hypoparathyroidism

Magnesium deficiency (magnesium is important for PTH secretion and action)

Question 10

Name the two types of metabolic bone disorders?

Answer 10

Abnormalities of formation (bone morphology)

Abnormalities in metabolism of bone

Question 11

Descirbe osteomalacia/rickets?

Answer 11

Same condition but:

Rickets in children

Osteomalacia in adults

Result of a loss of mineralisation.

Low levels of calcium means less calcium phosphate is formed. Decrease in the mineralisation of the matrix in bones.

Question 12

Describe how corticosteroid use induces osteoporosis?

Answer 12

Corticosteroids increase bone resorption rate and depth

Steroids block action of osteoblasts

Increase bone resorption

Reduced bone formation

Question 13

How can low phosphate levels have an effect on the level of calcium?

Answer 13

Phosphate is required to bind to calcium to produce calcium phosphate, a mineralised salt found in bones.

Low phosphate, less calcium bound to phosphate. Increase levels of calcium in the serum

Question 14

What are the clinical features of primary hyperparathyroidism?

Answer 14

Bones, Stones, Groans, Moans

Result of unregulated PTH secretion

Bones: PTH promotes osteoclasts to break down bones. Thus, high bone turnover.

Stones: Blood calcium levels are high. Increases the risk of kidney stones

Moans: Can induce mood changes

Groans: Can cause cramps

Question 15

If there is a high calcium level but normal PTH level, what is the first thing to think about?

Answer 15

Malignancy

Question 16

Describe Paget’s Disease?

Answer 16

Rapid bone turnover

Bone resorption and formation is increased

Disorganised structure as the deposit of bone is trying to keep up with the reabsorption.

Question 17

Describe osteopetrosis?

Answer 17

Genetic disorder

Increased bone density

Prone to breakage

Question 18

Describe osteogenesis imperfecta?

Answer 18

Also known as brittle bone disease

Genetic bone disorder

Defect in collagen type 1

Collagen type 1 is the main component of the organic part of bone.

Various types- depending on the severity.

Clinical signs: Recurrent childhood fractures, thinning of bones (as they are unable to bear weight)

Question 19

Describe Skeletal Fluorosis?

Answer 19

Excessive accumulation of fluroide in the bones.

Thus abnormal matrix mineralisation.

Bones are now harder and less elastin. Increase risk of fracture

Question 20

Describe space age bone disease?

Answer 20

Due to weightlessness

Bones do not have mechanical stress

Therefore reduction in the number of osteoblasts

Number of osteoclasts remain

Question 21

List a few bone remodelling defects and the rates of bone resorption and formation as a result?

Answer 21