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CEP > Parathyroid Hormone, Calcium and Bone > Flashcards

Parathyroid Hormone, Calcium and Bone Flashcards

1
Q

What are the target serum calcium levels?

A

2.1-2.6mM/L

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2
Q

What can calcium be bound to in circulation?

A

Albumin

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3
Q

What percentages of calcium are free and bound to albumin?

A

50% each

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4
Q

What is the half life of PTH?

A

8mins

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5
Q

What type of receptor does PTH bind to?

A

GPCR

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6
Q

What effect does hypocalcaemia have on PTH secretion?

A

Increases it

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7
Q

What effect does increased PTH secretion have on bone (and what is caused)?

A
  • Increased bone resorption
  • Increased serum calcium
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8
Q

What effect does increased PTH secretion have on kidney (and what is caused)?

A
  • Increased urinary phosphate (inc. bone resorption –> inc. serum calcium)
  • Decreased urinary calcium (inc. serum calcium)
  • Increased 1,25D3 production (inc. calcium + phosphate absorption in intestine –> inc. serum calcium + phosphate)
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9
Q

What is the active form of vitamin D?

A

1,25-dihydroxyvitamin D3 (1,25D3)

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10
Q

How is 1,25D3 produced?

A
  • Either vitamin D3 made from 7-dehydrocholesterol when UV light hits skin or obtained from source (eg. fish, eggs)
  • Liver converts vitamin D3 into 25-hydroxyvitamin D3 (25D3)
  • Kidney (with PTH) converts 25D3 to 1,25D3 using 1α-hydroxylase
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11
Q

Where is calcitonin produced?

A

Thyroid c-cells (parafollicular cells)

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12
Q

What stimulates calcitonin release?

A

Hypercalcaemia

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13
Q

What is the effect of calcitonin?

A

Inhibit bone resorption

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14
Q

What effect does hypercalcaemia have on PTH secretion?

A

Decreases it

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15
Q

What effect does decreased PTH secretion have on bone (and what is caused)?

A

Decreased bone resorption (dec. serum calcium)

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16
Q

What effect does decreased PTH secretion have on kidney (and what is caused)?

A
  • Decreased urinary phosphate (dec. bone resorption –> dec. serum calcium)
  • Increased urinary calcium (dec. serum calcium)
  • Decreased 1,25D3 production (dec. calcium + phosphate absorption in intestine –> dec. serum calcium + phosphate)
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17
Q

Where is fibroblast growth factor 23 (FGF23) produced?

A

Osteocytes

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18
Q

What effects does increased FGF23 have?

A
  • Increased urinary phosphate
  • Decreased urinary calcium
  • Suppresses renal synthesis of 1,25D3
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19
Q

What effect does hyperphosphataemia have on PTH secretion?

A

Increases it

20
Q

By action of what substances is serum phosphate reduced in hyperphosphataemia?

A
  • Mainly FGF23
  • Some PTH
21
Q

What is primary hyperparathyroidism?

A

Raised serum PTH due to a parathyroid tumour

22
Q

What does primary hyperparathyroidism cause?

A
  • Hypercalcaemia
  • Low serum phosphate
  • Loss of negative feedback from hypercalcaemia
23
Q

Symptoms of primary hyperparathyroidism

A
  • Lethargy/confusion
  • Thirst/polyuria
  • Renal stones
  • Constipation
  • Pancreatitis
  • Joint pain
  • Fracture
  • Depression
  • Hypertension
24
Q

How is primary hyperparathyroidism treated?

A

Surgery

25
Q

Difference between rickets and osteomalacia

A
  • Rickets affects growing skeleton (children)
  • Osteomalacia affects adult skeleton
26
Q

What is rickets/osteomalacia?

A

Deficiency of vitamin D (and/or calcium)

27
Q

What causes rickets/osteomalacia?

A
  • Lack of mineralisation of osteoid
  • Failure to absorb sufficient calcium from GIT
28
Q

What is osteoid?

A

Collagen component of bone

29
Q

Symptoms of rickets

A
  • Bow legs
  • Swollen joints
30
Q

Symptoms of osteomalacia

A
  • Bone pain
  • Pseudofractures
31
Q

How is rickets/osteomalacia treated?

A

Vitamin D replacement (dietary or through sunlight)

32
Q

What is secondary hyperparathyroidism?

A

Raised serum PTH secondary to renal disease

33
Q

Mechanism of how secondary hyperparathyroidism occurs

A
  • Abnormal kidney function (disease)
    > Dec. urinary phosphate
    > Inc. urinary calcium
    > Dec. 1,25D3 production
  • Bones sense raised serum phosphate levels and produce lots of FGF23
    > Further dec. 1,25D3 production
  • Intestine absorbs less calcium + phosphate
  • Hypocalcaemia feedback to parathyroid
    > Inc. PTH secretion
34
Q

How is secondary hyperparathyroidism treated?

A
  • Phosphate binders
  • Vitamin D analogues
35
Q

Symptoms of chronic kidney disease-mineral and bone disorder (CKD-MBD) and what causes them?

A
  • Osteomalacia-type symptoms
    > Dec. calcium and 1,25D3 after kidney disease (same as lead-up to secondary hyperparathyroidism)
  • Bone disease and increased fracture risk
    > Secondary hyperparathyroidism causes drastically increased PTH
    > Causes lots of bone resorption
36
Q

What is oncogenous osteomalacia (cause + result)

A
  • Caused by benign tumour secreting FGF23
  • Means high serum FGF23 and low serum 1,25D3
37
Q

What is X-linked hypophosphaemic rickets?

A

Mutations in PHEX gene lead to elevated FGF23 and suppressed 1,25D3

38
Q

What is osteoporosis?

A

Loss of bone mass/density (mineral and non-mineral bone decreased)

39
Q

Types of osteoporosis (description of each)

A
  • Osteoporosis of aging = gradual decline in bone density from early adult peak
  • Postmenopausal osteoporosis = rapid decline in female bone density following decline in estrogen at menopause
  • Steroid-induced osteoporosis = decline in bone density associated with use of steroids as therapy for inflammatory diseases
40
Q

Treatment options for osteoporosis

A
  • Hormone replacement therapy
    > Estrogen
  • Inhibition of osteoclast development
    > Denosumab is a RANK ligand antibody
    > Blocks RANK ligand on osteoblasts from interacting with RANK on osteoclasts
    > Decreased differentiation of pre-osteoclasts
  • Inhibition of osteoclast activity
    > Bisphosphonates disrupt intracellular enzymes required for osteoclast activity
  • Stimulation of osteoblast activity
    > Teriparatide is the first 34 AAs of PTH
    > Is anabolic stimulator of bone formation
41
Q

How can osteoporosis be prevented?

A
  • Exercise
  • Vitamin D and calcium
  • Avoid smoking
  • Avoid high alcohol intake
42
Q

Cell types in bone

A
  • Osteocytes
  • Osteoblasts
  • Osteoclasts
43
Q

Where are osteocytes found specifically?

A

Embedded in calcified bone matrix

44
Q

What do osteoblasts do?

A

Bone forming cells:
- Produce matrix constituents
- Aid calcification

45
Q

What do osteoclasts do?

A

Bone resorbing cells:
- Produce acid (resorbs mineral) and enzymes (resorb matrix)

46
Q

How are osteoclasts matured?

A
  • Originally osteoclast precursor
  • RANK ligand on osteoblast binds RANK on precursor
  • Makes mature osteoclast

CEP (14 decks)

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