3. Calcium Metabolism Flashcards
7 calcium dependant processes
1) Bone formation
2) Muscle contraction
3) Nerve conduction
4) Hormone release
5) Blood coagulation
6) Cell signalling
7) Enzyme cofactor
3 hormones that control bone endocrinology
1) Parathyroid (PTH) 2) Vitamin D 3)Calcitonin
Hydroxyapatite
Major Mineral of bone complex of Ca2+ and PO43-
What cell Builds bones
OsteoBlasts
What cell is responsible for bone resorption/breakdown?
Osteoclasts
5 roles of Vitamin D
1) Increases serum Ca2+
2) Facilitates intestinal absorption of calcium and phosphates
3) Increases bone resorption
4) Enhances PTH to promote renal tubular calcium reabsorption
Parathyroid hormone (PTH)
When extra cellular calcium falls PTH restores calcium level
Action of PTH on bone
High levels of PTH in response to low serum Ca2+ = inhibits osteoblasts and stimulates osteoclasts ( bone resorption) Low levels of PTH in response to high serum Ca2+ stimulates osteoblasts and inhibits osteoclasts ( bone formation)
Action of Calcitonin
released when calcium levels rise
decreases osteoclast activity
Phosphate %
bone = 84.97%
intracellular = 5%
extracellular = 0.03%
Factors increasing bone production
1) Growth hormone
2) Insulin-like growth factor
3) Local growth factors
4) Testosterone
5) Vitamin D
Factors reducing bone production
1) Corticosteroids 2) Staying in bed
Factors causing bone breakdown
1) PTH 2) Thyroid hormones
Factors reducing bone breakdown
1) Calcitonin 2) Oestrogen
Hypercalcaemia (high Ca2+ levels in serum) Symptoms
“Bones, moans and abdominal groans”
Causes of hypercalcaemia
1) Hyperparathyroidism
2) Vitamin D excess
3) Kidney Failure (secondary Failure)
4) Sarcoidosis – vitamin D sensitivity
Emergency management of hypercalcaemia
Calcium 2.6 to 2.9 mmol/L: - Send to outpatients If Calcium > 2.9 mmol/L - Urgent referral - Rehydrate with 0.9% saline - IV bisphosphonates*
Hypocalcaemia symptoms
1) Tingling of fingers, toes, lips 2) Painful bones 3) Tetany (muscle spasm) 4) Seizures
Causes of hypocalcaemia
1) Hypoparathyroidism
2) Vitamin D deficiency/ resistance
3) Magnesium deficiency
4) Pancreatitis
5) Hungry bone syndrome
Causes of Hypoparathyroidism
1) Destruction of the glands 2) Surgical removal
Treatment of hypocalcaemia
1) Calcium supplements
2) Vitamin D
Changes in bone density
- Increases until age 30 year - 10 % bone turnover per year - 0.5% bone loss per year - 1.5 % after menopause
Treatment of Osteoporosis in Women
- Bisphosphonate – first line - Oestrogen replacement - Calcitriol (Vit D) - Teriparatide
Treatment of Osteoporosis in Men
- Bisphosphonate – first line - Testosterone - Calcitriol
Osteomalacia
softening of the bones
caused by impaired bone metabolism
Causes of Osteomalacia
Vitamin D deficiency
Liver disease
Kidney disease
Malabsorption
Genetic causes
In children = RICKETS
In adults = OSTEOMALACIA
Paget’s disease
excessive breakdown of bone
followed by disorganized bone remodelling
Symptoms of Paget’s disease
Fractures
Bowed legs
Deformed skull
Deafness
Osteogenesis imperfecta
- a group of genetic disorders that mainly affect the bones
- results in bones that break easily
- white of the eye is blue! (bluish)
- hypermobility (double jointed)
- short height
- problems with the teeth
T-cell tolerance
T-cells that react with self too strongly in the thymus are eliminated
B-cell tolerance
B-cells with an antibody (receptor) that reacts with self are deleted in the bone marrow
Peripheral tolerance
results in non-responsiveness of B- and T- cells to peripheral antigens not expressed in the thymus/bone marrow
Anergy
functional non-responsiveness of a lymphocyte to antigen
Suppressor/Regulatory T-cells
CD4+
CD25+
Ankylosing Spondylitis
What secretes PTH
parathyroid glands
4 in the neck (primarily)
What secretes Calcitonin?
perifollicular cells of the thyroid gland
