Calcium Flashcards
Which three hormones are involved in regulating calcium and phosphate?
Vitamin D
Parathyroid hormone
Calcitonin
Which organs are involved in calcium homestasis?
Parathyroid gland Bone Kidney Gut Liver Skin
Why do calcium and phosphate levels need to be regulated?
Calcium is important for muscle contraction and nerve conduction.
Phosphate is needed for energy.
What stimulates release of parathyroid hormone from the parathyroid gland?
Low plasma calcium concentration
Describe the functions of parathyroid hormone
Acts to raise plasma calcium.
Stimulates release of calcium and phosphate from bone.
Stimulates 1-alpha-hydroxylase enzyme in the kidney (this enzyme converts vitamin D into its active form).
Increases reabsorption of calcium from the distal tubule of the kidney.
What is the active form of vitamin D?
Calcitriol
1,25-dihydroxy Vitamin D3
Describe the role of calcitriol
Stimulates bone to release calcium and phosphate into the blood.
Inhibits parathyroid gland (negative feedback).
Increases absorption of calcium and phosphate from the gut tube.
Increases reabsorption of calcium from the proximal tubule in the kidney.
Describe the role of calcitonin
Acts to decrease plasma calcium levels.
Released from thyroid gland in response to high plasma calcium concentration.
Role is less significant in humans than that of parathyroid hormone.
Describe the symptoms of hypocalcaemia
MSK: Paraesthesia, muscle spasms, seizures
CV: Prolonged QT interval, hypotension, heart failiure, papilloedema
Describe the symptoms of hypercalcaemia
MSK: Muscle weakness, bone pain, osteoporosis
CV: Short QT interval, hypertension
Renal: Polyuria, renal dysfunction, diabetes insipidus
GI: Anorexia, nausea, vomiting, constipation, pancreatitis
Confusion, fatigue
How is hypercalcaemia treated?
Rehydration
IV bisphosphonates
(Surgery)
What roles does calcium have in the body?
Acts as a signalling molecule
- required for neurotransmitters/hormones, muscle contraction and enzyme function
Blood clotting - part of the clotting cascade
Apoptosis
Skeletal strength
Influences neurone excitability - calcium makes membranes LESS permeable to sodium
Describe the effect of low calcium on membrane excitability
Hypocalcaemia increases neuronal sodium permeability, which leads to hyperexcitation of neurones.
- in extreme cases this causes tetany
- causes asphyxiation if tetany spreads to larynx and respiratory muscles
Describe the effect of hypercalcaemia
Decreases neuronal sodium permeability which reduces excitation.
- depressed neuromuscular activity
- can trigger cardiac arrhythmias
