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Biochemistry > Calcium And Bone > Flashcards

Calcium And Bone Flashcards

1
Q

Where is calcium found?

A

99% in the bone, 0.9% in soft tissue and 0.1% in ECF

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2
Q

What is the basic unit of bone?

A

The osteon

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3
Q

What does the osteon consist of?

A

A hollow laminated rod of collagen and CaPO4

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4
Q

What is the Haversian canal?

A

it is a nutrient channel that runs through the osteon that contains a blood vessel and sometimes a nerve

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5
Q

How is bone formed?

A

Bone osteoblasts

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6
Q

What do you call layers of osteoblasts that build up around the central canal.

A

Lamellae

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7
Q

What are the small channels that connect the Lamellae and the central canal called?

A

Canaliculi

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8
Q

How are substances exchanged between the bone and the circulation?

A

Through none fluid in the canaliculi

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9
Q

What are the two main structures of the bone?

A

1) extracellularly matrix

2) cellular constituents

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10
Q

What are the main components of ECM?

A

Mineral

Colloid

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11
Q

What is the mineral component of ecm?

A

Mineral form of calcium
Calcium phosphate
Magnesium
Fluoride

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12
Q

What is the purpose of type 1 collagen in ecm?

A

Forms a fibrillar structure by cross linkage of the precursor peptide procollagen

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13
Q

What is the structure of lamellar bone?

A

Fibrils are arranged in parallel or concentric sheets

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14
Q

What is the structure of woven bone?

A

The arrangement of fibrils is more random and therefore weaker

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15
Q

What is the porosity of cortical (compact) bone and where is it found?

A

5-10% porosity - found in long bones

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16
Q

What is the porosity of trabecular bone (spongey/cancellous) and where is it found?

A

50-90%. Found in the ends of long bones, in vertebrae and flat bone eg. Pelvis

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17
Q

True or false: compact bone makes up 80% of skeletal mass but 20% of bone turnover?

A

True

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18
Q

What % of bone is made up of osteoblasts?

A

4-6% of skeletal cells

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19
Q

What percentage of skeletal cells are osteoclasts?

A

1-2%.

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20
Q

What are the 2 main roles of osteocytes?

A

Cross talk between osteocytes via cell extensions into canaliculi
Key role in bone remodelling in response to mechanical stress

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21
Q

What are the 3 main steps of resorption in bone remodelling?

A

1) osteoclasts bind to bone matrix
2) Osteoclast form and acidic micro environment which mobilises bone mineral
3) exposed osteoid is degraded by lysosomal enzymes

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22
Q

Main steps of remodelling?

A

Osteoblasts move to the reabsorption cavity.

2) unmineralised osteoid synthesised by osteoblasts fills the resorption cavity
3) osteoid is mineralised
4) osteoblasts trapped in bone become osteocytes and stop secreting osteoid
5) bone surface is covered by lining cells and a thin layer of unmineralised osteoid

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23
Q

What is normal plasma calcium?

A

2.2-2.6mmol/L

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24
Q

What percentage of plasma calcium is ionised, protein bound and complexed (with sulphate and phosphates)

A

Ionised =40-50%
Protein bound = 40-50%
Complexed= 5-10%

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25
Q

What hormone regulates calcium?

A

Parathyroid hormone

26
Q

How much albumin would bind to 0.02mmol/L of calcium?

A

1g/L

27
Q

How is vitamin d synthesised?

A

From cholesterol in skin exposed to sunlight

28
Q

How is vitamin D activated?

A

By hydroxylation of a carbon 1 in the kidneys and carbon 25 in the liver

29
Q

What % of calcium is reabsorbed in the tubules?

A

98%

30
Q

In the proximal tubule what is calcium reabsorption linked to?

A

Na reabsorption

31
Q

What regulates the 10% of ca reabsorbed in the distal tubule?

A

PTH. Higher the PTH the more that is reabsorbed

32
Q

What can hyperparathyroidism (mostly due to benign adenoma) cause?

A

Hypercalcaemia

33
Q

Why does hypercalcaemia of malignancy occur?

A

PTHrP released by malignancies - similar to PTH.

Also can be due to metastatic deposits in bone

34
Q

Why does polyurea and polydipsia occur in hypercalcaemia?

A

Renal tube becomes resistant to ADH

35
Q

Why cardiac arrest associated with hypercalcaemia?

A

Because of the role of ca in neuromuscular excitability

36
Q

Why is hypocalcaemia associated with renal failure?

A

Damage or loss of kidney parenchyma means a loss of activity of 1-alpha hydroxyl enzyme (required to activate vitamin d)

37
Q

Why is hypocalcaemia found in acute pancreatitis?

A

Lipase released from an inflamed pancreas may begin to auto digest fats in the abdominal cavity- form glycerol and fatty acids. The fatty acids Sponify calcium taking it out of circulation

38
Q

What would you expect of PTH and alk phos in hypocalcaemia?

A

High PTH and high alk phos(increased bone turnover)

39
Q

What are the symptoms of hypocalcaemia

A

Signs of neuromuscular excitability- cramps, convulsions

40
Q

What is it called when there is a problem with bone quantity?

A

Osteoporosis

41
Q

What is a disorder of bone mineralisation?

A

Rickets, osteomalacia

42
Q

What is a disorder of bone turnover

A

Paget’s disease

43
Q

What is osteoporosis?

A

An imbalance between resorption and formation of bone

44
Q

Who suffers for hypogonadism?

A

Post menopausal women
Anorexia nervous a
Athletes

45
Q

What bone disorder is hypogonadism and excess glucocorticoids associated with?

A

Osteoporosis

46
Q

Vertebral body osteoporosis is associated with osteoporosis secondary to what?

A

Hypogonadism or glucocorticoid excess

47
Q

What group are more susceptible to hip osteoporosis?

A

Usually >65 years

48
Q

What Dual energy X-Ray absorptiometry (DEXA) scan results show osteoporosis?

A

-2.5 SD of ref range

49
Q

What is osteomalacia?

A

A delay in mineralisation as osteoid is layed down.

50
Q

What are the main skeletal changes of rickets?

A

Affects growing ends of long bones

51
Q

Causes of rickets?

A

Vit d deficiency or abnormal Vit d metabolism (renal disease)

52
Q

What are the symptoms of rickets?

A

Malaise, bone pain, proximal muscle weakness

53
Q

In rickets what results do u expect from alkaline phosphatase, ca, phosphate, Vit d and PTH?

A 
Alk phos raised
Ca low or normal 
Phosphate low
Vit d low
PTH raised
54
Q

What is Paget’s disease?

A

Focal disorder of bone remodelling

55
Q

How many people with Paget’s disease have a family history of it?

A

40%

56
Q

What characterises Paget’s disease?

A

Accelerated bone turnover
Initiated by increased osteoclasts mediated resorption
Abnormal bone remodelling

57
Q

Neoplasticism complications are associated with what bone disorder?

A

Paget’s disease

58
Q

What test results would you expect from a patient with Paget’s disease?

A

Elevated alkaline phosphate
Normal everything else
Exclude alk phos due to liver disease

59
Q

What is a marker of bone formation?

A

Alkaline phosphatase (produced by osteoblasts)

60
Q

What is a marker for bone resorption?

A

CTX (carboxy-terminal collagen cross links)

Biochemistry (8 decks)

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