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Calcium Flashcards

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1
Q

Is acute low or high serum calcium more dangerous

A

Low

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2
Q

Are endocrine mechanisms for preventing hypocalcemia or hypercalcemia stronger

A

Hypocalcemia

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3
Q

dietary sources of calcium

A

Dairy products

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4
Q

How does calcium enter the circulation

A

dietary sources, or occasionally an IV infusion

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5
Q

Where is calcium stored

A

skeleton

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6
Q

How is calcium removed

A

via kidneys

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7
Q

Where is calcium stored

A

Skeleton

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8
Q

What percentage of skeletal calcium is interchangeable with free extracellular calcium

A

1%

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9
Q

What forms can calcium be in in the body

A

Protein bound
Ionised
Complexed

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10
Q

What proteins is some calcium bound to

A

Albumin
Globulin

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11
Q

What is the biologically active form of calcium

A

Ionised calcium

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12
Q

When does ionised calcium level change when total body calcium stays the same

A

Acid base status change

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13
Q

Why does serum ionised calcium decrease in alkalosis

A

Ca2+ binds to same site on albumin as H+ so more calcium is bound

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14
Q

What symptoms is felt when serum calcium falls

A

Lip tingling

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15
Q

Roles of calcium in the body

A

Muscle contraction
Neurotransmitter
Hormone release
Maintaining electrochemical gradient across cell membrane

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16
Q

What can low serum calcium lead to

A

Tachyarrhythmia
Tetany

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17
Q

How does hypocalcemia cause tachyarrhythmia and tetany

A

Ca stabilises voltage gated na channels
Hypocalcemia Increases permeability of excitable membranes in nerves and muscles to Na+, reducing threshold for action potential firing

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18
Q

What form is almost all serum calcium in

A

Ionised

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19
Q

Responding to low serum calcium is the primary role of which gland

A

Parathyroid

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20
Q

How does the parathyroid hormone increase serum calcium

A

Mobilises calcium form bone
Reduces calcium lost at kidneys
Increases proportion of dietary calcium absorbed via activation of vitamin D

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21
Q

What other ion is released when calcium is released from bone

A

Phosphate

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22
Q

Why does parathyroid hormone cause phosphate loss in urine

A

Allow excretion of phosphate released from bones with calcium

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23
Q

What cell types make up the parathyroid gland

A

Chief cells
Oxyphil cells

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24
Q

What do chief cells secrete in the parathyroid

A

Parathyroid hormone

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25
What imaging is used to assess parathyroid pathologies
Technetium sestamibi scintigraphy
26
How long is the half life of PTH in circulation
2 mins
27
What is the major stimulus for PTH secretion
Fall in conc of serum ionised calcium
28
Where are calcium sensing receptors which detect low serum calcium
Cell surface
29
How does magnesium impact PTH secretion
Small decrease - stimulate PTH release Chronic severe decrease - blocks PTH secretion + causes cellular resistance to PTH
30
How can magnesium decrease cause hypocalcemia
Severe magnesium decrease blocks PTH secretion and causes tissue level PTH resistance
31
How does normal/high serum calcium affect PTH
Decreases PTH secretion Breaks down stored PTH suppresses transcription of PTH gene
32
Familial hypocalciuric hypercalcemia
Condition caused by an inactivating mutation of the calcium sensing receptor in cells, resetting the normal range of serum calcium at a higher level with no significant clinical effects
33
Cinacalcet
Drug - Allosteric modulator of calcium sensing receptor to decrease PTH
34
What drug can be given to patients with hyperparathyroidism to decrease PTH secretion
Cinacalcet
35
Why does vitamin D deficiency elevate PTH levels
Vitamin D suppresses PTH transcription
36
How does PTH affect bones
Increases calcium and phosphate resorption
37
How does PTH affect intestines
Increases calcium and phosphate absorption
38
How does PTH affect kidneys
Decreases calcium excretion and increases phosphate excretion
39
Where in the kidney tubule is calcium reabsorbed
Proximal tubule and loop of henle
40
What are the 2 routes of calcium reabsorption in the kidney
Paracellular route Trans cellular route
41
What drives calcium reabsorption in the kidney
Voltage gradient across cells
42
How do loop diuretics decrease calcium reabsorption
Impair voltage gradient across tubule cells by binding to NAK2Cl channels in loop of henle
43
How does PTH increase kidney calcium reabsorption
Upregulates channels and transporters - TRPV calcium channels, calcium ATPase, Na/Ca exchanger
44
How do loop diuretics affect serum calcium level
Decrease
45
How do thiazide diuretics affect serum calcium level
Increase
46
Why does PTH Downregulate NaPi transporters
Reduce phosphate reabsorption
47
Why does PTH upregulates 1 alpha hydroxylase
To activate vitamin D
48
How does PTH effect Na H2O and HCO3 resorption
Inhibits
49
How does PTH effect glucose metabolism
Causes proximal tubule Gluconeogenesis
50
How does PTH activate osteoclasts
Increases RANK ligand production Decreases OPG production
51
What are the main constituents of bone
Collagen Hydroxyapatite
52
What is the main effect of vitamin D on bone
Provides calcium from gut to facilitate mineralisation
53
What type of molecule is vitamin D
Hormone - not a vitamin
54
Where is basic vitamin D converted to 25(OH)D
Liver
55
Which enzyme is needed to convert 25OH)D3 to the calcitriol
1 alpha hydroxylase
56
Why does kidney damage cause hypocalcemia
Decr calcium absorbtion from food due to Lack of activated vitamin D as kidney produces 1 alpha hydroxylase
57
Where are vitamin D receptors
Mostly on nucleus Some on cell membrane
58
How does activation of the vitamin D receptor cause negative feedback
Inhibits 1 alpha hydroxylase preventing production of more activated vitamin D
59
When does activation of the vitamin D receptor cause positive feedback and serum hypercalcemia
In macrophages fighting granulomatous disease eg TB
60
Calcitriol
Active form of vitamin D
61
What is the major role of calcitriol
Increase gut absorption of calcium and phosphate
62
How does vitamin D deficiency affect bones
Impairs remineralisation making bones soft
63
What conditions are caused by vitamin D deficiency in adults and children
Children - rickets Adults - osteomalacia
64
What causes osteoporosis
Long term elevated PTH release
65
Which hormone is the most important in phosphate level regulation
FGF23
66
How does low phosphate affect bones
Impairs bone mineralisation
67
What can cause osteomalacia
Vitamin D deficiency Low serum phosphate
68
What type of mutation causes familial rickets
FGF23 actuvating Mutation
69
What marker is released when thyroid C cells become neoplasticism in medullary thyroid cancer
Calcitonin
70
What causes hypercalcemia of malignancy
PTH-related peptide paraneoplastic release from cancers
71
What can hypercalcemia cause
Constipation Depression Kidney stones Nephrogenic diabetes insipidus
72
Main cause of hypocalcemia
Hypoparathyroidism
73
Causes of hypoparathyroidism
Removal of glands in neck surgery Autoimmune conditions Genetic conditions Severe vitamin D deficiency Chronic kidney disease - decr activated vit D
74
Causes of hypercalcemia
Hyperparathyroidism Malignancy
75
What causes primary hyperparathyroidism
Parathyroid tumour releasing excess PTH
76
What causes secondary hyperparathyroidism
Natural response to low calcium or vit d deficiency
77
What causes tertiary hyperparathyroidism
Parathyroid hyperplasia, usually due to CKD Autonomous PTH production following secondary hyperparathyroidism

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