Calcium Metabolism 1

Question 1

Function of Calcium?

Answer 1

Calcium causes depolarisation and is therefore essential for

• > Nervous activity
• > Muscle Control

Question 2

Describe the flow of Calcium through the body?

Answer 2

Calcium enters through the gut.

Calcium is excreted in the urine.

Question 3

Describe how Calcium is stored in the body?

Answer 3

99% of Calcium is stored in the skeleton (Calcium Reservoir) - along with Phosphate and Magnesium.

The remaining 1% is exists in the Serum in 3 Forms - Total Serum Calcium is 2.2-2.6mmol/L

i) Free ‘ionised’, 50% BIOLOGICALLY ACTIVE
ii) Protein bound, 40% - Albumin
iii) Complexes, 10% i.e. Citrate*/Phosphate

*Blood transfusions with Citrate present can chelate the bloods calcium and cause a Hypocalcaemia

Question 4

What is Corrected Calcium?

Answer 4

Corrected Calcium = Measured total Ca + (0.02*40-Albumin)

-> Normal Albumin is 40g/L, and each g/L carries 0.02mmol/L

Question 5

What level of serum calcium will be there in a patient with chronic liver disease and why?

Answer 5

• > Many patients have Hypoalbuminaemia as a result of Chronic Liver Disease etc.
• > Their total serum calcium will therefore be lower, but the amount of Biologically Active, Free Ionised Calcium will be normal

Question 6

What is the most reliable way to measure Serum Free Calcium?

Answer 6

Arterial Blood Gas

Question 7

How does pH affect Calcium?

Answer 7

• > H+ and Ca+ both compete for Albumin
• > In Alkalosis, H+ leaves the Albumin and more Ca+ is taken up therefore reducing the amount of Serum Free Biologically Active Ca+ (Hypocalcaemic)
• > In Acidosis, H+ is taken up the Albumin, displacing Ca+ therefore the patient will show symptoms of Hypercalcaemia

Question 8

What are the 2 key hormones in calcium homeostasis?`

Answer 8

Vitamin D and PTH

Question 9

What is Vitamin D2 – Ergocalciferol?

Answer 9

The plant version of Vitamin D3

Question 10

How can 1-alpha hydroxylase be aberrantly produced?

Answer 10

Physiologically – Kidney (under PTH)

Pathologically – Lung (Sarcoidosis

Question 11

What does Osteoblast activity cause?

Answer 11

Raised ALP

• Post Fracture
• Certain Bone Diseases

Question 12

What is Osteoporosis?

Answer 12

Thinning of bones due to loss of bone density (normal mineralisation and structure)
-> Loss of bone mass
Physiological part of ageing i.e. loss of bone mass, but in Osteoporosis it occurs quicker

Question 13

Risk factors for osteoporosis?

Answer 13

• > Failure to attain peak bone mass in childhood
• > Early menopause (Earlier increased deceleration in bone mass)
• > Age
• > Lifestyle; Alcohol, Smoking, Poor Diet
• > Endocrine Causes – Thyrotoxicosis, Hyperprolactinaemia, Cushings
• > Iatrogenic - Steroids

Question 14

What is usually the first presenting complaint of someone with osteoporosis?

Answer 14

-> Fracture is usually first symptom (Neck of femur, vertebral, Wrist i.e. Colle’s)

Question 15

Investigations for osteoporosis?

Answer 15

• > Biochemistry, Ca and Phosphate normal
• > DEXA Scan

DEXA - Dual Energy X Ray Absorptiometry 
T - Score >-1 Normal
T - Score [-1 to -2.5] Ostepaenia
T - Score < -2.5 Osteoporosis
NB Raised Bone Density - Osteosclerosis

T Score – S.D. from mean of young healthy population (useful for #risk)
Z Score – S.D from mean of age-matched control (useful to identify accelerated bone loss)

Question 16

Management of osteoporosis

Answer 16

Conservative

• > Weight bearing exercises
• > Stop Smoking
• > Reduce alcohol

Medical

• > Vit D + Calcium
• > Bisphosphonates i.e. Alendronate -> Inhibits Osteoclast mediated bone-resorption
• > Teriparatide (PTH derivative)
• > Strontium Ranelate -> Stimulates Osteoblasts and Inhibits Osteoclasts
• > Raloxifene // HRT -> Oestrogen like effects

Question 17

What is osteomalacia?

Answer 17

Metabolic bone disorder caused by Vitamin D Deficiency

-> Abnormal decalcified bone [Demineralised]

Question 18

Risk factors and epidemiology of osteomalacia

Answer 18

Epidemiology
Over 50% of adults have a Vitamin D Deficiency
-> 16% are severely deficient during winter and spring

Risk Factors

• > Lack of sunlight
• > Dark Skin
• > Dietary / Gut Malabsorption
• > Renal Failure
• > Older AntiConvulsants i.e. Phenytoin induce Vitamin D breakdown
• > Chappati’s, Phytic Acid chelates Vitamin D

Question 19

What are the features of osteomalacia?

Answer 19

• > Bone and muscle pain
• > Increased Fracture Risk
• > LOW Ca, High PTH, LOW Phosphate, Raised ALP (Osteoblast function)
• > Looser Zones, Pseudofractures i.e. fracture secondary to insufficiency of bone

Question 20

What is osteomalacia known as in childhood? and what are some features/

Answer 20

In Childhood - Osteomalacia is known as Rickets

• > bowed legs
• > costochondral swellings
• > widened epiphyses at the wrists
• > myopathy

Question 21

What is Paget’s disease?

Answer 21

Focal disorder of bone remodelling

-> Unknown aetiology i.e. may be due to a virus

Question 22

What are the main presenting symptoms of paget’s disease?

Answer 22

-> Pain, warmth, deformity
-> Nerve compression, malignancy, and cardiac failure
Typically Affects;
-> Pelvis, Femur, Skull, Tibia

Question 23

What are the investigations for paget’s?

Answer 23

• > Bloods; Raised ALP

- > Radioactive bisphosphonate injection – Technetium Bisphosphonate Scan.

Question 24

What is the treatment for paget’s?

Answer 24

-> Treated with Bisphosphonates i.e. Alendronate

Question 25

What is Parathyroid Bone Disease?

Answer 25

o.e. Osteitis Fibrosa

Increased PTH, causing Bone Resorption; Loss of Cortical Bone

Question 26

What is Renal Osteodystrophy?

Answer 26

Aluminium Toxicity from Dialysis inhibits 1alpha Hydroxylase

-> Low Calcium, Secondary increased PTH.

Question 27

What is the normal total serum calcium?

Answer 27

2.2 - 2.6 mmol/L

Question 28

Why does Paget’s disease sometimes present as malignancy?

Answer 28

Fewer than 5% of patients with Paget’s disease will undergo malignant transformation to a sarcoma. The risk of a patient developing a sarcoma is greater the more extensive the Paget’s disease and the longer the patient has been affected.

Question 29

Why does Paget’s disease sometimes present with cardiac failure?

Answer 29

Paget’s disease causes increased blood flow to the bones, and sometimes it is difficult for the heart to keep up with the demand for increased blood flow. This can lead to heart failure.