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Calcium Flashcards

1
Q

What are the functions of calcium?

A

bone and tooth structure, mineral store, action potentials, membrane excitability, second messenger, co-factor in metabolic pathways, blood clotting factor

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2
Q

How can we be certain that cause of tooth weakness after development is not due to Ca deficiency?

A

detine/enamel cannot be broken down to recover Ca because odontoclasts/ameloclasts do not exist

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3
Q

Examples of Ca acting as a second messenger

A

muscle (excitation-contraction coupling), gland secretion, non-steroid hormone action (non-steroid therefore cannot penetrate membrane)

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4
Q

What is meant by diffusible calcium?

A

calcium that is available - it is either ionised or bound to citrate

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5
Q

What is the concentration of ionised calcium?

A

1.2 mmol/l

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6
Q

What is the concentration of diffusible calcium bound to citrate?

A

0.2mmol/l

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7
Q

What is non-diffusible calcium?

A

calcium that’s bound to proteins

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8
Q

What is the concentration of calcium bound to protein (non-diffusible)?

A

1.2 mmol/l

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9
Q

What is the total concentration of calcium in the body?

A

2.6 mmol/l (diffusible 1.4 + non-diffusible 1.2)

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10
Q

Where do we get calcium from?

A

our diet

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11
Q

Where is calcium absorbed from our diet?

A

GI tract

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12
Q

What happens to the calcium that is not absorbed in the GIT?

A

the calcium is excreted in faeces

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13
Q

What is the name of the type of bone that is remodelled to achieve Ca balance?

A

exchangeable bone

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14
Q

What is the name of the type of bone that is not demineralised/remodelled?

A

stable bone

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15
Q

Where does the Ca that is absorbed from the GIT go?

A

Ca enters the plasma and interstitial fluid

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16
Q

How is excess Ca excreted from the plasma?

A

blood is filtered by the kidneys and excess Ca is excreted in urine

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17
Q

How does Ca become incorporated into bone?

A

Ca from the plasma/interstitial fluid is used to mineralise osteoid of exchangeable bone which then becomes stable bone

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18
Q

Which substances are required for calcium homeostasis?

A

parathyroid hormone, calcitonin, vitamin D

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19
Q

Where is PTH secreted from?

A

parathyroid glands

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20
Q

When in PTH secreted?

A

when plasma [Ca2+] is low

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21
Q

Function of PTH

A

increases plasma calcium

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22
Q

How does PTH increase plasma calcium?

A

increased bone resorption, increased Ca2+ resorption in kidney (in exchange with decreased PO4 resorption), increased Ca2+ uptake from intestines (assisted by vit D)

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23
Q

Which cells carry out bone resorption?

A

osteoclasts

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24
Q

What is the effect of PTH on the kidney?

A

increases Ca2+ resorption, increases PO4 excretion, increases 1,25 (OH)2 vit D (calcitriol) formation

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25
What is the effect of PTH on bone?
bone resorption - releases Ca2+ and PO4
26
What is the overall effect of PTH on PO4 concentration?
no effect - although there is increased PO4 excretion from kidney, bone resorption releases PO4
27
How is absorption of Ca from the intestines increased?
PTH increases the formation of 1,25 (OH)2 vit D (calcitriol) in the kidneys which aids the absorption of Ca from the GIT
28
Where is calcitonin secreted from?
C cells (parafollicular) in the thyroid gland
29
When is calcitonin released?
When plasma [Ca2+] is high
30
What is the function of calcitonin?
reduces plasma [Ca2+]
31
How does calcitonin lower plasma calcium?
increases bone formation and decreases Ca2+ resorption in the kidneys
32
Which cells are involved in bone formation?
osteoblasts
33
Why does it seem that calcitonin does not play a major role in calcium homeostasis?
a lack of calcitonin has no pathological effects
34
What is the effect of calcitonin on kidneys?
increases Ca2+ excretion
35
What is the effect of calcitonin on bone?
increases bone deposition
36
Where is vitamin D derived from?
dietary vitamin D and 7-dehydrocholesterol synthesised in the skin
37
What is the name of the precursor to vitamin D synthesised in the skin in sunlight?
7-dehydrocholesterol
38
What is the first product from dietary vitamin D and 7-dehydrocholesterol?
vitamin D3 (cholecalciferol)
39
What is vitamin D3 (cholecalciferol) converted into?
25 (OH) cholecalciferol
40
How is vitamin D3 (cholecalciferol) converted into 25 (OH) cholecalciferol?
vitamin D3 (cholecalciferol) is hydroxylated by 25-hydroxylase in the liver
41
Where is vitamin D3 (cholecalciferol) hydroxylated into 25 (OH) cholecalciferol?
in the liver by 25-hydroxylase
42
What is 25 (OH) cholecalciferol converted into?
1,25 (OH)2 cholecalciferol (calcitriol)
43
How is 25 (OH) cholecalciferol converted into 1,25 (OH)2 cholecalciferol?
hydroxylated by 1a (alpha) hydroxylase in the kidney
44
Which enzyme converts 25 (OH) cholecalciferol into 1,25 (OH)2 cholecalciferol (calcitriol)?
1 alpha hydroxylase (in the kidney)
45
Which hormone regulates the hydroxylation of 25 (OH) cholecalciferol into 1,25 (OH)2 cholecalciferol in the kidney?
PTH
46
What is the active form of vitamin D?
1,25 (OH)2 cholecalciferol (calcitriol)
47
What is the overall function of 1,25 (OH)2 cholecalciferol (calcitriol)?
increase plasma Ca and PO4
48
How does 1,25 (OH)2 cholecalciferol (calcitriol) increase plasma Ca and PO4?
increases Ca absorption from intestines, increase Ca and PO4 retention in kidneys, and increases Ca and PO4 release from bone
49
What is the effect of 1,25 (OH)2 cholecalciferol (calcitriol) on the intestine?
increases Ca absorption in intestine
50
What is the effect of 1,25 (OH)2 cholecalciferol (calcitriol) on the kidneys?
increases Ca and PO4 retention
51
What is the effect of 1,25 (OH)2 cholecalciferol (calcitriol) on bone?
increases Ca and PO4 release
52
What is a similarity in the effects of vitamin D (calcitriol) and PTH?
both increase plasma [Ca]
53
What is a difference between the effects of PTH and vitamin D (calcitriol)?
PTH doesn't affect [PO4] as PO4 excretion from kidney is increased whereas calcitriol increases PO4 retention in the kidneys resulting in an overall [PO4] increase (bone resorption increases PO4 too)
54
Which hormones increase bone formation/mass?
calcitonin, growth hormone, IGF-1, insulin, oestrogen, testosterone
55
Which hormones increase bone resorption and therefore decrease bone mass?
cortisol, parathyroid hormone, thyroid hormones
56
Function of osteoblasts
synthesis and secrete collagen fibres forming a matrix (osteoid) which is later mineralised by calcium salts
57
How do osteocytes arise?
when osteoblasts become trapped in the matrix they mature into osteocytes
58
Where are osteocytes found?
in bony lacunae
59
How do osteocytes communicate?
via long cytoplasmic processes
60
Describe the structure of an osteoclast
a large, multinucleate cell
61
What cells are osteoclasts derived from?
monocyte/macrophage lineage
62
Function of osteoclasts
resorb bone
63
Where are osteoclasts found?
in depressions called Howship's lacunae
64
What concept underpins orthodontic treatment?
bone remodelling
65
Function of bone remodelling
allows a constant source of Ca
66
What is the term for raised [Ca2+]?
hypercalcaemia
67
What is the term for reduced [Ca2+]?
hypocalcaemia
68
What condition may result from low calcium levels in the blood?
Hypocalcaemic tetany
69
What does hypocalcaemic tetany cause?
involuntary muscle contractions
70
What are the causes of hypocalcaemic tetany?
decreased Ca2+ intake, excessive Ca2+ loss, alkalosis
71
What is alkalosis?
condition where blood plasma pH is too high
72
How can alkalosis contribute to hypocalcaemia?
a high blood plasma pH increases protein binding of calcium which decreases ionised calcium (diffusible)
73
How does low [Ca2+] impact nerve excitability?
low [Ca2+] increases nerve excitability
74
What are the symptoms of low [Ca2+]?
pins and needles, muscle spasms
75
What are the 2 clinical indicators of hypocalcaemia?
Trousseau's sign and Chvostek's sign
76
What is Trousseau's sign?
involuntary contractions of muscles in hand and wrist due to hypocalcaemia
77
What is Chvostek's sign?
tapping of the facial nerve resulting in muscle contraction due to hypocalcaemia
78
What can cause alkalosis?
hyperventilation (increase in O2 which expels more CO2 causing increase alkalinity of blood)
79
What is the treatment for alkalosis due to hyperventilation?
trapping CO2 in the lungs by rebreathing expired air from a bag
80
Which hormones can cause calcium regulation disorders if they are over or under secreted?
parathyroid hormone, vitamin D, calcitonin
81
What is the consequence of hyperparathyroidism?
increased bone resorption
82
Which condition can result from hyperparathyroidism?
osteitis fibrosa cystica
83
What is osteitis fibrosa cystica?
areas of demineralisation in skull and leg bones
84
What is unusual about the name of the disease, osteitis fibrosa cystica?
it names features that do not occur in the condition - there is no inflammation of the bone, no fibrous tissue or cysts
85
How would osteitis fibrosa cystica be diagnosed?
no infection, no cysts, teeth vital. Panoramic radiograph of the skull shows other areas of radiolucency / lesions. Refer to GP to test [Ca2+]
86
What consequence does hypoparathyroidism have on teeth?
defective teeth mineralisation due to low blood [Ca2+] from under secretion of PTH (congenital as enamel is not broken down following development)
87
What is the cause of vitamin D deficiency?
dietary deficiency results in failure to synthesise 1,25 (OH)2 cholecalciferol (calcitriol)
88
What are the consequences of vitamin D deficiency?
decreased Ca uptake from GIT, undermineralised bone causing a lack of rigidity
89
What is the condition of a lack of bone rigidity in children?
rickets
90
What is the name of the condition in which adults lack bone rigidity?
osteomalacia
91
Cause of rickets / osteomalacia
vitamin D deficiency
92
What are the symptoms of rickets?
bowlegged, cowboy walk, flexible bones
93
What are the consequences of increased or decreased calcitonin levels?
no obvious clinical consequences - so calcitonin is likely not essential for plasma [Ca2+] regulation
94
Which bone disease results in a decreased bone mass and density?
osteoporosis
95
Which bone disease results in an increased bone mass and density?
osteopetrosis
96
Which part of the population is more affected by osteoporosis?
elderly
97
Although osteoporosis affects both men and women, why is it evident earlier in women?
due to menopause (decreased oestrogen)
98
Causes of osteoporosis
menopause, corticosteroids (cortisol increases bone resorption), nutritional deficiency
99
How does osteopetrosis affect blood supply?
osteopetrosis reduces blood supply
100
What are the consequences of osteopetrosis?
bone is prone to fracture and chronic infection, difficult extractions and healing
101
Why is bone healing reduced in osteopetrosis?
due to reduced blood vessels
102
Why are tooth roots indistinct from bone on radiographs in patients with osteopetrosis?
osteopetrosis results in more radiopaque bone which is difficult to distinguish from teeth
103
How do the maxilla and mandible compare in osteopetrosis?
mandible is enlarged and has a greater density than mandible

BDS1 (105 decks)

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