Chem path 1 - calcium metabolism

Question 1

What % of calcium is in the serum?

Answer 1

1%, the other 99% in the bone

Question 2

What are the 3 forms in which calcium can be found?

Answer 2

Free, ionised (50%) (biologically active, maintained at a fixed level)
Albumin bound (40%)
Complexed with citrate/phosphate (10%)

Question 3

What is the equation for corrected calcium?

Answer 3

Corrected calcium = Serum Ca + 0.02 (40-albumin g/l)

Question 4

What can corrected calcium be used for?

Answer 4

To show if the problem with calcium is to do with albumin or not

Question 5

What will happen to calcium if albumin is low?

Answer 5

Bound calcium will be low but free calcium will be normal

Question 6

What are the actions of PTH?

Answer 6

1 alpha hydroxylation of vit D –> calcidiol to calcitriol –> increased gut absorption of calcium AND phosphate
Bone: osteoclast activation
Direct renal calcium resorption and phosphate excretion

Question 7

Two main hormones involved in calcium homeostasis

Answer 7

PTH and VitD

Question 8

What kind of hormone is vitamin D?

Answer 8

Steroid hormone (any hormone derived from cholesterol)

Question 9

What are the 2 forms of vitamin D?

Answer 9

Vitamin D2 - ergocalciferol (plants)

Vitamin D3 - cholecalciferol (humans).

Question 10

When measuring vitamin D levels, which form of vitamin D is detected?

Answer 10

25-hydroxycholecalciferol

Question 11

Outline the process of vitaminD synthesis

Answer 11

7-dehydrocholesterol + UVB–> cholecalciferol –> 25-hydroxycholecalciferol (liver 25-hydroxylase enzyme) –> activated by 1a-hydroxylase (under PTH control) –> 1,25-dihydroxycholecalciferol (Calcitriol)

Question 12

What three elements is bone a reservoir of?

Answer 12

Calcium
Phosphate
Magnesium (important in the synthesis of PTH)

Question 13

Radiological feature of osteomalacia

Answer 13

Looser’s zones (pseudofractures)

Question 14

Features of rickets

Answer 14

Bowing of legs
Costochondral swelling
Myopathy
Widened epiphyses at the wrist

Question 15

Whcih class of drugs induce the breakdown of vitamin D?

Answer 15

Anticonvulsants e.g. phenytoin

Question 16

Why do chappatis cause vit D deficiency?

Answer 16

Contain a high level of phytic acid which chelates vitD in the gut and reduces absorption

Question 17

Diagnosis of osteoporosis

Answer 17

T-score (

Question 18

Example of a SERM

Answer 18

Raloxifene

Question 19

What is the commonest cause of hypercalcaemia?

Answer 19

Primary hyperparathyroidism

Question 20

How does the parathyroid gland detect calcium levels?

Answer 20

Through the CaSR

Question 21

Name of condition with mutation in CaSR

Answer 21

Familial hypocalcuric/benign hypercalcaemia (AD)

Question 22

Outlline brief pathophys of FHH/FBH

Answer 22

CaSR mutation, loss of sensitivity to calcium levels, higher setpoint for PTH release, mild hypercalcaemia, reduced urine Ca

Clinically normal as all bodily receptors do not detect calcium

Question 23

3 types of hypercalcaemia in malignancy

Answer 23

Humoral hypercalcaemia of malignancy (PTHrp e.g. SCLC)
Bone mets e.g. breast Ca
Haematological malignancy e.g. myeloma

Question 24

Which drug activates CaSR?

Answer 24

Cinacalcet acid

Question 25

Other causes of non-PTH driven hypercalcaemia

Answer 25

Sarcoidosis
Thyrotoxicosis (bone resorption) 
Hypoadrenalism
Thiazide diuretics
Excess vit D (sun beds)

Question 26

Which 2 signs are seen in hypocalcaemia?

Answer 26

Chvostek’s (Face)

Trousseau’s (Carpopedal spasm)

Question 27

Hypocalcaemia ECG changes

Answer 27

Long QT interval

Question 28

What syndrome has congenital absence of parathyroids?

Answer 28

DiGeorge’s

Question 29

What physical characteristic is pseudohypoparathyroidism associated with?

Answer 29

SHORT 4TH METACARPAL (Albright’s hereditary osteodystrophy)

Question 30

Deficiency in which electrolyte can cause hypoparathyroidism?

Answer 30

Magnesium

Question 31

What drug can reduce your Mg2+ levels?

Answer 31

Omeprazole

Question 32

What investigation is done for Paget’s?

Answer 32

Nuclear med scan

Question 33

If primary hyperparathyroidism is left for years, what secondary condition develops?

Answer 33

Osteitis fibrosa cystica