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CEP > Parathyroid Gland > Flashcards

Parathyroid Gland Flashcards

1
Q

List 3 types of functions of the skeleton.

A

1 - Mechanical.

2 - Protective.

3 - Metabolic.

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2
Q

List 4 substances involved in calcium homeostasis.

A

1 - Parathyroid hormone (PTH).

2 - Vitamin D.

3 - Calcitonin.

4 - Fibroblast growth factor 23 (FGF23).

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3
Q

List 3 diseases of bone.

A

1 - Hyperparathyroidism.

2 - Osteomalacia.

3 - Osteoporosis.

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4
Q

What proportion of serum calcium is free?

To which molecule is the rest of the calcium bound?

A
  • 50%.

- The rest is bound to albumin.

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5
Q

How many parathyroid glands are there?

A

4.

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6
Q

List the factors that stimulate the parathyroid gland to secrete parathyroid hormone.

A

1 - Low calcium.

2 - High phosphate.

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7
Q

List 4 actions of parathyroid hormone.

A

1 - Increases calcium reabsorption and decreases phosphate reabsorption in the renal distal tubule.

2 - Increases both calcium and phosphate reabsorption in the intestine via activation of vitamin D.

3 - Increases calcium release from bone via activation of osteoclasts.

4 - Decreases phosphate reabsorption.

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8
Q

How many amino acids comprise the parathyroid hormone?

Which of these amino acids are responsible for its biological activity?

A
  • 84 amino acids in total.

- The first 34 amino acids are responsible for its biological activity.

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9
Q

What is the normal adult reference range for parathyroid hormone?

A

1.6-6.9 pmol/L.

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10
Q

To which receptors does parathyroid hormone bind?

Where in the body are these receptors found?

A

Parathyroid hormone binds to GPCRs mainly in the kidney and osteoblasts.

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11
Q

Describe the negative feedback mechanism for parathyroid hormone.

A
  • PTH transcription is inhibited by 1,25-(OH)2 D3.

- PTH transcription is also inhibited by increased serum calcium.

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12
Q

What is the difference between vitamin D2 and vitamin D3?

A

Vitamin D2 is of plant origin whereas vitamin D3 is of animal origin.

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13
Q

Are vitamin D receptors extracellular or intracellular?

A

Intracellular (vitamin D is a steroid).

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14
Q

List 2 dietary sources of vitamin D

A

1 - Eggs.

2 - Fish.

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15
Q

What is the precursor to vitamin D?

A

7-dehydrocholesterol.

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16
Q

What is vitamin D3 converted into?

A

25-hydroxyvitamin D3.

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17
Q

What role does the liver play in vitamin D synthesis?

A

It is responsible for the conversion of vitamin D3 into 25-hydroxyvitamin D3.

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18
Q

What role does the kidney play in vitamin D synthesis?

Which hormone stimulates the kidney to carry out this role?

A
  • It is responsible for the conversion of 25-hydroxyvitamin D3 into 1,25-dihydroxyvitamin D3.
  • PTH stimulates the kidney to do this.
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19
Q

Which form of vitamin D binds to the vitamin D receptor?

A

1,25-dihydroxyvitamin D3.

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20
Q

What is the function of vitamin D3?

A

To increase calcium and phosphate reabsorption at the intestine.

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21
Q

Which form of vitamin D is measured clinically?

A

25-hydroxyvitamin D3.

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22
Q

What is the normal adult reference range for vitamin D?

A

7.5 - 50 nmol/L.

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23
Q

List the names of each form of vitamin D by which they are commonly known.

A
  • Vitamin D: Calciferol.
  • 25-(OH) D: Calcidiol.
  • 1,25-(OH)2 D: Calcitriol.
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24
Q

Which cells produce calcitonin?

A

Thyroid c-cells.

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25
Q

What stimulates calcitonin release?

A

Hypercalcaemia.

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26
Q

What is the action of calcitonin?

A

Inhibition of bone breakdown via direct effect on osteoclasts.

27
Q

List 3 actions of parathyroid hormone on the kidney.

A

1 - Increases urinary phosphate.

2 - Decreases urinary calcium.

3 - Stimulates 1,25-hydroxyvitamin D3 production.

28
Q

Where is fibroblast growth factor 23 produced?

A

Osteocytes and osteoblasts.

29
Q

What stimulates fibroblast growth factor 23 production?

A

High serum phosphate.

30
Q

List 2 functions of fibroblast growth factor 23.

A

1 - To increase renal excretion of phosphate.

2 - To suppress renal synthesis of vitamin D (further reducing serum phosphate).

31
Q

Of which disease is high fibroblast growth factor 23 an indicator?

A

Renal disease.

32
Q

List 3 non-collagenous proteins that are essential to bone function.

A

1 - Osteocalcin.

2 - Osteonectin.

3 - Osteopontin.

33
Q

How is the extracellular matrix of bone calcified?

A

With the formation of hydroxyapatite crystals (containing both calcium and phosphate).

34
Q

List 3 cell types within bone.

A

1 - Osteocytes.

2 - Osteoblasts.

3 - Osteoclasts.

35
Q

What is the primary function of osteocytes?

A

Maintenance of the strength of the extracellular matrix of bone.

36
Q

Describe the location and structure of osteocytes.

A
  • They are embedded in the calcified bone matrix that they produce.
  • They have a stellate shape with long processes that contact other osteocytes and osteoblasts.
37
Q

From which cells do osteoblasts originate?

A

Mesenchymal stem cells.

38
Q

List 2 functions of osteoblasts.

A

1 - To form the extracellular matrix of bone.

2 - To aid calcification.

39
Q

What is the function of osteoclasts?

A

To reabsorb the contents of bone into the blood.

40
Q

Where are osteoclasts found?

A

In contact with calcified bone surfaces (e.g. in lacunae / depressions).

41
Q

How do osteoclasts reabsorb the contents of bone?

A

By producing acid (to resorb the minerals) and enzymes (to resorb the matrix).

42
Q

Give an example of a histologically distinctive characteristic of osteoclasts.

A

They are multinucleated.

43
Q

Via which proteins do osteoclasts attach to the bone surface?

A

Integrins.

44
Q

Describe the process of bone remodelling.

A

1 - Reversal phase (creating an osteogenic environment at the apex of the lacuna).

2 - Osteoid formation (unmineralised bone).

3 - Mineralisation of the osteoid.

45
Q

What is a metabolic bone disease?

A

Any of:

1 - Hyperparathyroidism.

2 - Rickets (osteomalacia).

3 - Renal osteodystrophy.

4 - Osteoporosis.

46
Q

What might cause primary hyperparathyroidism?

A

A parathyroid tumour.

47
Q

List 2 complications of hyperparathyroidism.

A

1 - Hypercalcaemia.

2 - Hypophosphataemia.

48
Q

What might cause secondary hyperparathyroidism?

How?

A
  • Renal disease.

- Renal disease would increase serum phosphate and decrease activation of vitamin D.

49
Q

How can secondary hyperparathyroidism be treated?

A
  • Phosphate binders.

- Vitamin D analogues.

50
Q

What is tertiary hyperparathyroidism?

A

Where long-standing secondary hyperparathyroidism leads to irreversible parathyroid hyperplasia.

51
Q

How can tertiary hyperparathyroidism be treated?

A

Surgery.

52
Q

What is the difference between osteoporosis and osteomalacia?

A
  • Osteomalacia is characterised by poor mineralisation of bone (leading to soft bone).
  • Osteoporosis is characterised by low bone density, although the composition of bone is normal (leading to porous and brittle bone).
53
Q

What is the difference between rickets and osteomalacia?

A

Osteomalacia in children is known as rickets.

54
Q

Describe renal osteodystrophy.

A
  • A renal disease resulting in osteomalacia (a cause of secondary hyperparathyroidism).
  • Urinary phosphate decreases, urinary calcium increases and 1,25-(OH)2 D3 decreases.
55
Q

List 3 causes of rickets / osteomalacia.

A

1 - Failure to absorb sufficient Ca2+ from the GI tract.

2 - Lack of sunlight.

3 - Lack of dietary Ca2+.

56
Q

What is necessary to convert 7-dehydrocholesterol into vitamin D3?

A

UV light.

57
Q

What causes the bowed legs seen with rickets?

A

A weak osteoid at the growth plates.

58
Q

What causes the swollen joints seen with rickets?

A

Excess growth of growth plates as a compensatory mechanism for weak growth plates.

59
Q

Where in a long bone are the growth plates found?

A

Between the epiphyses and metaphyses.

60
Q

List 2 signs and symptoms of osteomalacia.

A

1 - Bone pain.

2 - Pseudofractures.

61
Q

How is rickets / osteomalacia treated?

A

Vitamin D replacement.

62
Q

What causes postmenopausal osteoporosis?

A

A decline in oestrogen, which increases the rate of bone remodelling and bone reabsorption (breakdown).

63
Q

What are the long-term consequences of spinal osteoporosis?

A

A kyphotic spine.

64
Q

What is the importance of phosphate?

A

It is necessary for bone calcification (as the hydroxyapatite crystals contain both calcium and phosphate).

CEP (15 decks)

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