Lecture 14 - Calcium metabolism Flashcards
What is the parathyroid gland formed from embryologically?
Third and fourth brachial artery
Where and how many PTH glands?
- Behind thyroid glands
- x4
What are some importance of calcium?
- Hormone secretion (insulin)
- Muscle contraction
- Nerve conduction
- Exocytosis
How is calcium vital for bone formation?
Ca+K: Hydroxyapatite crystals, a major component of bone
What regulates Ca conc. in blood?
- PTH + calcitriol
How does PTH affect calcium and K homeostasis?
- PTH ⬆️, K ⬇️
- ⬆️Ca reabsorption from kidney
- ⬆️osteoclast resoption –> increase bone turnover
- ⬆️absorption of Ca from food (small intestine)
What types of Vit. D are present in the diet?
- Ergocalciferol (D2): obtain from mushrooms (less potent version of vit D
- Cholecalciferol (D3): Liver of fatty fish
How does Vit D act in Ca & K homeostasis?
- Decrease PTH production
- ⬆️Ca reabsorption from kidney
- ⬆️mineralisation of Ca to bone
- ⬆️absorption of Ca and K from food (small intestine)
What parameters define hypercalcaemia?
- Serum calcium >2.51mmol/L
>3 is severe
What are some symptoms of hypercalcaemia?
- Moans –> Constipation
- Bones –> bone aches
- Stones –> Kidney stones
- Groans –> Confusion
- Thirst and polyuria
What indication does high calcium and low PTH show?
N.B PTH can drive hypercalcaemia
- High Ca due to diff factor (not PTH from parathyroid gland)
- Most likely= cancer –> produce PTH like peptide
What are some examples of cancers with high calcium?
- Myeloma (blood cancer)
- Bone metastases (Bronchus, Thyroid, Breast, Kidney)
Other than cancers what can be a cause of high Ca and low PTH?
- TB
- Sarcoidosis: growth of tiny cancers in lung
- Granulomas that secrete calcitriol
What does high Ca and high PTH suggest?
- Not cancer
- Primary hyperparathyroidism: benign parathyroid adenoma
What are the effects of primary hyperparathyroidism?
- High Ca, Low K
- ⬆️bone turnover
What is the treatment for acute severe hypercalcaemia (medical emergency–> SEVERE DEHYDRATION)?
- Fluid into veins (normal saline 0.9%)
- Treat underlying cause
What are the parameters of hypocalcaemia?
- Serum Ca <1.9mmol/L
- Symptoms severe if sudden drop
What does hypocalcaemia result in?
- Hyperexcitability of NS (neuromuscular junction)
- Leads to paraesthesia (pins & needles), tetany (involuntary muscle contraction), paralysis, convulsions
What are some causes of hypocalcaemia?
- Vit D deficiency
- Hypoparathyroidism
How does low vit D result in secondary hyper-PTH?
- Low Vit D –> low Ca/K –> High PTH
- Stimulation of Ca sensing receptors reduces PTH
What are some causes of Vit D deficiency? And what does it result in adults or children if severe?
- Lack of sunlight
- Dietary deficiency
- GI disease
- Kidney disease
- Pigmented or covered skin
- Result in rickets in children, osteomalacia in adults
What is the diff. btw osteoporosis and osteomalacia?
- Osteomalacia = normal structure of bone but under mineralised
- Osteoporosis= structurally degraded but fully mineralised
What does osteomalacia result in?
Low Ca
- Gluteal muscle weakness leads to waddling gait (bend legs)
- Multiple fractures
What is the levels of substances in hypo-PTH?
- Low Ca & PTH
- High K
What are some causes of hypo-PTH?
look out for scar in neck
- Surgical removal/damage of PTH gland
- Pathology of PTH gland
- Failure of 3rd or 4th brachial artery
How to treat acute severe hypo-PTH?
a med emergency
- Assess airway and conscious level
- ECG monitor for heart
- Intravenous Ca and monitoring
List some risk factors for osteoporosis.
- Menopausal women
- Smoking and immobile
- Endocrine disease (hypo-PTH)
- Family history
What are some sources of Ca?
- Diet (Dairy products major source)= 800-1200mg per day
- Intestine net uptake is 175mg/day (same as Ca excreted in urine)
- Bone calcium deposition (controlled by K) is 280mg/day
- Kidney reabsorb Ca
How is free Ca (biologically active) measured?
- Total Ca measured: Free ionised/ Bound to albumin/ Bound to low-molecular weight organic anions (citrate)
- Levels adjusted depending on albumin
What are effects of PTHrP?
related peptide
- Increase Ca release from bone
- Reduce renal Ca excretion
- Reduce renal absorption
- X increase renal C-1 hydroxylase –> calcitriol X increase
How much Ca in body?
- 1kg
- Vast majority of this present in the skeleton and teeth. Soft tissues contain about 10g of calcium and approx 1g is present in the extracellular fluid.
How many PTH glands are there in a human body?
4
What type of hormone is PTH?
Peptide hormone
How does PTH exert its effects on the GI tract?
- Indirectly through promoting the formation of calcitriol
How do principal cells in these glands sense plasma calcium concentration?
GPCR activated by calcium
