Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Musc- OBG > Metabolic Bone Disease – Biochemistry > Flashcards

Metabolic Bone Disease – Biochemistry Flashcards

1
Q

What is metabolic bone disease?

A

A group of disease that cause a change in bone density and bone strength by increasing bone resorption, decreasing bone formation or altering bone structure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the five main metabolic bone disorders?

A

Primary Hyperparathyroidism

Osteomalacia/Rickets

Osteporosis

Renal Osteodystrophy

Paget’s Disease

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the main components of bone strength?

A

Mass

Material/ mineralisation

Microarchitecture

Macroarchitectue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

When is peak bone mass reached?

A

Around 25 years

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

When does bone mass begin to decline?

A

Around 40 years

NOTE: in women, the decline in bone mass accelerates after menopause

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How are microfractures repaired?

A

Bone remodelling

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Briefly describe the bone remodelling cycle.

A

A microcrack crosses the canaliculi and severs the osteocyte processes, inducing osteocyte apoptosis

This signals to the surface lining cells, which release factors to recruit cells from the blood and marrow to the remodelling compartment

Osteoclasts are generated locally and resorb the matrix and the microcrack

Then osteoblasts deposit new lamellar bone
Osteoblasts that become trapped in the matrix become osteocytes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the normal range for serum calcium concentration?

A

2.15-2.56 mmol/L

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the distribution of calcium.

A

46% plasma protein bound (albumin)

47% free calcium

7% complexes (with phosphate or citrate)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the ‘corrected’ calcium level?

A

This compensates for changes in protein level (if proteins are high, itcompensates down)

Corrected calcium = [Ca2+] + 0.02(45-[albumin])

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe the effect of metabolic alkalosis on calcium distribution.

A

It makes more calcium bind to plasma proteins thus reducing the free calcium levels

NOTE: venous stasis may elevate free calcium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the two main targets of PTH?

A

Kidneys

Bone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe the effects of PTH in:

a. Bone
b. Kidneys

A

a. Bone
Acute release of available calcium (not stored in hydroxyapatite crystal form)
More chronically, increased osteoclast activity

b. Kidneys
Increased calcium reabsorption
Increased phosphate excretion
Increased stimulation of 1-alpha hydroxylase (thus increasing calcitriol (1,25 dihydroxyvitD) production)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Where does the PTH-mediated increase in calcium reabsorption take place in the nephron?

A

DISTAL convoluted tubule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Where does the PTH-mediated increase in phosphate excretion take place in the nephron?

A

PROXIMAL convoluted tubule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is PTH dependent on?

A

Magnesium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the half-life of PTH?

A

8 mins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What else can the PTH receptor be activated by other than PTH?

A

PTHrP (PTH related protein)

This is produced by some tumours

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What does the parathyroid gland use to monitor serum calcium?

A

Calcium-sensing receptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Describe the relationship between PTH level and calcium in vivo.

A

Steep inverse sigmoid function

NOTE: there is a minimum level of PTH release (it can’t get below this even in the case of hypercalcaemia)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are the causes of primary hyperparathyroidism?

A

Parathyroid adenoma (80%)

Parathyroid hyperplasia (20%)

Parathyroid cancer

Familial syndromes-rare

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What biochemical results are diagnostic of primary hyperparathyroidism?

A

Elevated total/ionised calcium

With PTH levels frankly elevated or in the upper half of the normal range (negative feedback should drop PTH if there is hypercalcaemia)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are the clinical features of primary hyperparathyroidism?

A

Stones, Bones, Abdominal Groans and Psychic Moans:

  • Stones – renal colic, nephrocalcinosis
  • Bones – osteitis fibrosa cystica
  • Abdominal moans – dyspepsia, pancreatitis, constipation
  • Psychic groans – depression, impaired concentration

NOTE: patients may also suffer fractures secondary to the bone resorption
IMPORTANT NOTE: hypercalcaemia also causes diuresis (polyuria and polydipsia)

24
Q

What is the main site of action of calcitriol and what effect does it have?

A

Small intestine – increases calcium and phosphate absorption

25
Q

Describe the effects of calcitriol on bone and in the kidneys.

A

Facilitates PTH effect on the DCT in the kidneys (increased calcium reabsorption)

Synergises with PTH in the bone to increase osteoclast activation/maturation

26
Q

Which receptors/proteins are involved in mediating the effects of calcitriol on the intestines?

A

TRPV6

Calbindin

27
Q

What parameter is used to determine whether a patient is vitamin D deficient?

A

Deficient < 20 ng/M (50 nmol/L)

Normal > 30 ng/M (75 nmol/L)

28
Q

What is Rickets?

A

Inadequate vitamin D activity leads to defective mineralisation of the cartilaginous growth plate (before a low calcium)- in children

29
Q

State some signs and symptoms of Rickets.

A

Symptoms:
 Lack of play
 Bone pain and tenderness (axial)
 Muscle weakness (proximal)

Signs: 
 Age dependent deformity 
 Myopathy 
 Hypotonia  
 Short stature  
 Tenderness on percussion
30
Q

State some Vitamin D related causes of Rickets/Osteomalacia.

A

Dietary deficiency

Malabsorptoin

Drugs – e.g. enzyme inducers such as phenytoin

Chronic renal failure

Rare hereditary

31
Q

For each of the following state whether it would be high, low or normal in the serum of a Rickets patient:

a. Calcium
b. Phosphate
c. Alkaline Phosphatase
d. 25-OH cholecalciferol
e. PTH
f. URINE phosphate

A

a. Calcium
Normal or Low

b. Phosphate
Normal or Low

c. Alkaline Phosphatase
High

d.25-OH cholecalciferol
Low

e. PTH
High

f. URINE phosphate
High

32
Q

Other than PTH, what else can cause increased phosphate excretion?

A

FGF23

33
Q

What effect does this factor have that is unlike PTH?

A

It inhibits 1 alpha-hydroxylase, thus inhibiting calcitriol production

34
Q

Which cells produce this factor? (FGF23)

A

Osteoblast lineage cells

35
Q

Other than Vitamin D deficiency, what else can cause Rickets/Osteomalacia?

A

Phosphate deficiency

36
Q

State some phosphate-related conditions that cause Rickets/Osteomalacia.

A

X-linked Hypophosphataemic Rickets (mutation in Phex (this cleaves FGF23))

Autosomal Dominant Hypophosphataemia Rickets

Oncogenic Osteomalacia (mesenchymal tumours can produce FGF23)

37
Q

What can cause osteoporosis due to increased bone resorption and decreased bone formation?

A

Glucocorticoids

38
Q

How does oestrogen deficiency lead to a decrease in bone mineral density?

A

It increases the number of bone remodelling units

It causes an imbalance in bone remodelling with increased bone resorption compared to bone formation

39
Q

Describe the biochemistry of someone with osteoporosis.

A

Everything should be normal if the cause is primary

40
Q

What is the single best predictor of fracture risk?

A

BMD

41
Q

What is used to measure BMD?

A

DEXA scans

42
Q

Which bones are used when measuring BMD and why?

A

Vertebral bodies
 Commonest fracture
 Good measure of cancellous bone
 It is a highly metabolically active bone so it is quick to respond to treatment

Hip – second commonest fracture

NOTE: fracture risk assessment tool (FRAX) uses hip BMD

43
Q

Which chains make up type 1 collagen?

A

2 x alpha 1

1 x alpha 2

44
Q

What can be used as a marker of bone formation that is linked to collagen production?

A

Procollagen type 1 N-terminal propeptide (P1NP)

45
Q

What can be used as a measure of bone resorption that is linked to collagen production?

A

C-terminal telopeptide (CTX) – serum

N-terminal telopeptide (NTX) – urine

3 hydroxylysine molecules on adjacent tropocollagen fibrils condense to form a pyridinium ring linkage
These can be measured

46
Q

After how long do bone resorption markers fall?

A

4-6 weeks

47
Q

What are the problems with cross-linking collagen, with regards to measurement of bone markers?

A

Reproducibility- this is difficult

Positive association with age

Need to correct for creatinine

Diurnal variation in urine markers

48
Q

What bone formation marker is commonly in use?

A

Alkaline Phosphatase

49
Q

What is it (Alkaline Phosphatase) used in the diagnosis and monitoring of?

A

Osteomalacia

Paget’s

Bone Metastases

50
Q

What is P1NP being used for now?

A

Used as a predictor of response to anabolic treatments

51
Q

What are the two forms of alkaline phosphatase?

A

Liver

Bone

52
Q

Which bone diseases will cause a rise in ALP?

A

Osteomalacia

Bone metastases

Also hyperparathyroidism and hyperthyroidism

53
Q

How does alkaline phosphatase change with age?

A

Increases markedly during puberty reaching its highest levels

Remains relatively constant following puberty (potential small rise after the age of 50)

54
Q

What biochemical changes occur in renal osteodystrophy?

A

Increased serum phosphate

Reduction in calcitriol (vitD)

55
Q

Describe the sequelae (diseases secondary to–>) of renal osteodystrophy.

A

Secondary hyperparathyroidism

This is unsuccessful and hypocalcaemia develops

This leads to excessive stimulation of the parathyroid glands, leading to parathyroid hyperplasia

The parathyroid cells begin to reduce expression of calcium-sensing receptors (CSR) and Vitamin D receptors (VDR) and become autonomous (tertiary)

This causes hypercalcaemia

Musc- OBG (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions