Biochemistry part 2 Flashcards
List some endocrine causes of osteoporosis
Hypogonadism
Primary hyperparathyroidism
Primary hyperparathyroidism
List another cause of osteoporosis
Multiple myeloma
What might the urinary calcium levels be in someone with osteoporosis?
Might be high
How does DEXA work?
Measures the transmission through the body of X-rays of two different photon energies
Which two parts of the body are measured in DEXA?
Vertebra
Hip
Why is the BMD of vertebra measured in DEXA?
Vertebra is the most common site of fracture
Vertebra is made of cancellous, metabolic bone and this responds quickly to treatment
What is the second most common site of fracture in osteoporosis?
Hip
Which of the two BMD measurements does the fracture risk assessment tool (FRAX) use?
Hip BMD
What can be used to measure type 1 collagen formation?
P1NP in blood - Procollagen type 1 N-terminal Propeptide
Which three chains join to form type 1 collagen?
2 x alpha 1 chains
1 x alpha 2 chains
What is P1NP and when is it produced?
Procollagen type 1 N-terminal peptide is cut off from the sides of tropocollagen as it’s being made
Which two markers can be used to measure bone resorption?
Measure carboxy-terminal collagen crosslinks (CTX) in the serum
Or urinary N-telopeptide (NTX)
How do CTX and NTX form?
3 hydroxylysine molecules on adjacent tropocollagen fibrils condense to form a pyridinium ring linkage using telopeptides
What effect do anti-resorptive drugs have on BMD?
Bone resorption markers fall in 4-6 weeks
What happens to urinary NTx after anti-resorptive drugs, and what is the time frame?
50% drop of urinary NTx by 3 months
What are the problems with using cross-links?
Low reproducibility
Positive association with age
Need to correct for creatinine
Diurnal variation with urine markers
What is a better way of measuring bone formation?
Alkaline phosphatase
List three conditions in which alkaline phosphatase is used for diagnosis and monitoring
Paget’s
Osteomalacia
Boney metastases
What is the updated use of P1NP?
As a predictor of response to anabolic treatments
List five sites of alkaline phosphatase production
Liver Bone Intestine Germ cells Placenta
What are the two actions of bone-specific alkaline phosphatase?
Mineralisation
Regulates concentrations of phosphocompounds
What is the half life of BSAP?
40 hours
List five conditions in which bone specific alkaline phosphatase may be high
Paget's disease Osteomalacia Bone metastases Hyperparathyroidism Hyperthyroidism
What is the immediate result of chronic kidney disease?
Phosphate retention
Low calcitriol
Acidosis
What does the acidosis result in?
Demineralisation
What results from low calcitriol?
Hypocalcemia
Secondary hyperparathyroidism Bone resorption
Osteomalacia
What results from phosphate retention?
Metastatic heterotopic calcification (as the excess phosphate binds to calcium anywhere in the body)
