Biochemistry part 2

Question 1

List some endocrine causes of osteoporosis

Answer 1

Hypogonadism
Primary hyperparathyroidism
Primary hyperparathyroidism

Question 2

List another cause of osteoporosis

Answer 2

Multiple myeloma

Question 3

What might the urinary calcium levels be in someone with osteoporosis?

Answer 3

Might be high

Question 4

How does DEXA work?

Answer 4

Measures the transmission through the body of X-rays of two different photon energies

Question 5

Which two parts of the body are measured in DEXA?

Answer 5

Vertebra

Hip

Question 6

Why is the BMD of vertebra measured in DEXA?

Answer 6

Vertebra is the most common site of fracture

Vertebra is made of cancellous, metabolic bone and this responds quickly to treatment

Question 7

What is the second most common site of fracture in osteoporosis?

Answer 7

Hip

Question 8

Which of the two BMD measurements does the fracture risk assessment tool (FRAX) use?

Answer 8

Hip BMD

Question 9

What can be used to measure type 1 collagen formation?

Answer 9

P1NP in blood - Procollagen type 1 N-terminal Propeptide

Question 10

Which three chains join to form type 1 collagen?

Answer 10

2 x alpha 1 chains

1 x alpha 2 chains

Question 11

What is P1NP and when is it produced?

Answer 11

Procollagen type 1 N-terminal peptide is cut off from the sides of tropocollagen as it’s being made

Question 12

Which two markers can be used to measure bone resorption?

Answer 12

Measure carboxy-terminal collagen crosslinks (CTX) in the serum
Or urinary N-telopeptide (NTX)

Question 13

How do CTX and NTX form?

Answer 13

3 hydroxylysine molecules on adjacent tropocollagen fibrils condense to form a pyridinium ring linkage using telopeptides

Question 14

What effect do anti-resorptive drugs have on BMD?

Answer 14

Bone resorption markers fall in 4-6 weeks

Question 15

What happens to urinary NTx after anti-resorptive drugs, and what is the time frame?

Answer 15

50% drop of urinary NTx by 3 months

Question 16

What are the problems with using cross-links?

Answer 16

Low reproducibility
Positive association with age
Need to correct for creatinine
Diurnal variation with urine markers

Question 17

What is a better way of measuring bone formation?

Answer 17

Alkaline phosphatase

Question 18

List three conditions in which alkaline phosphatase is used for diagnosis and monitoring

Answer 18

Paget’s
Osteomalacia
Boney metastases

Question 19

What is the updated use of P1NP?

Answer 19

As a predictor of response to anabolic treatments

Question 20

List five sites of alkaline phosphatase production

Answer 20

Liver
Bone
Intestine
Germ cells
Placenta

Question 21

What are the two actions of bone-specific alkaline phosphatase?

Answer 21

Mineralisation

Regulates concentrations of phosphocompounds

Question 22

What is the half life of BSAP?

Answer 22

40 hours

Question 23

List five conditions in which bone specific alkaline phosphatase may be high

Answer 23

Paget's disease
Osteomalacia 
Bone metastases 
Hyperparathyroidism 
Hyperthyroidism

Question 24

What is the immediate result of chronic kidney disease?

Answer 24

Phosphate retention
Low calcitriol
Acidosis

Question 25

What does the acidosis result in?

Answer 25

Demineralisation

Question 26

What results from low calcitriol?

Answer 26

Hypocalcemia
Secondary hyperparathyroidism Bone resorption
Osteomalacia

Question 27

What results from phosphate retention?

Answer 27

Metastatic heterotopic calcification (as the excess phosphate binds to calcium anywhere in the body)