Calcium Metabolism 1 Flashcards
(29 cards)
Function of Calcium?
Calcium causes depolarisation and is therefore essential for
- > Nervous activity
- > Muscle Control
Describe the flow of Calcium through the body?
Calcium enters through the gut.
Calcium is excreted in the urine.
Describe how Calcium is stored in the body?
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
What is Corrected Calcium?
Corrected Calcium = Measured total Ca + (0.02*40-Albumin)
-> Normal Albumin is 40g/L, and each g/L carries 0.02mmol/L
What level of serum calcium will be there in a patient with chronic liver disease and why?
- > 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
What is the most reliable way to measure Serum Free Calcium?
Arterial Blood Gas
How does pH affect Calcium?
- > 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
What are the 2 key hormones in calcium homeostasis?`
Vitamin D and PTH
What is Vitamin D2 – Ergocalciferol?
The plant version of Vitamin D3
How can 1-alpha hydroxylase be aberrantly produced?
Physiologically – Kidney (under PTH)
Pathologically – Lung (Sarcoidosis
What does Osteoblast activity cause?
Raised ALP
- Post Fracture
- Certain Bone Diseases
What is Osteoporosis?
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
Risk factors for osteoporosis?
- > 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
What is usually the first presenting complaint of someone with osteoporosis?
-> Fracture is usually first symptom (Neck of femur, vertebral, Wrist i.e. Colle’s)
Investigations for osteoporosis?
- > 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)
Management of osteoporosis
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
What is osteomalacia?
Metabolic bone disorder caused by Vitamin D Deficiency
-> Abnormal decalcified bone [Demineralised]
Risk factors and epidemiology of osteomalacia
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
What are the features of osteomalacia?
- > 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
What is osteomalacia known as in childhood? and what are some features/
In Childhood - Osteomalacia is known as Rickets
- > bowed legs
- > costochondral swellings
- > widened epiphyses at the wrists
- > myopathy
What is Paget’s disease?
Focal disorder of bone remodelling
-> Unknown aetiology i.e. may be due to a virus
What are the main presenting symptoms of paget’s disease?
-> Pain, warmth, deformity
-> Nerve compression, malignancy, and cardiac failure
Typically Affects;
-> Pelvis, Femur, Skull, Tibia
What are the investigations for paget’s?
- > Bloods; Raised ALP
- > Radioactive bisphosphonate injection – Technetium Bisphosphonate Scan.
What is the treatment for paget’s?
-> Treated with Bisphosphonates i.e. Alendronate
