Summary
Summary Calcium homeostasis
- Institution
- University Of East Anglia
Neurophysiology, synaptic pharmacology and endocrinology - 2nd semester Includes bullet points, key diagrams and images
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Calcium Homeostasis Low calcium increases sodium permeability and vice versa
Hypocalcaemia- increases muscle/nerve excitability causing spasms
Hypercalcaemia- decreases muscle/nerve excitability so can cause arrhythmias
Bones and teeth act as calcium reservoirs
Bone has crystalline hydroxyapatite which precipitates around collagen extra-
cellular matrix
High levels of calcium in bone fluid
Osteoblasts- deposit bone and secrete collagen matrix
Osteoclasts- bone resorption where enzymes and HCl dissolve bone
Parathyroid
Parathyroid hormone secretion increases when plasma levels of calcium are low
and acts to increase them
Parathyroid cells have calcium sensing receptors (GPCRs)
PTH acts on bone, kidneys and GIT
Causes calcium release from bone breakdown which increases levels in the
plasma
Fast Exchange
PTH causes rapid efflux of calcium from bone fluid
PTH receptors on osteoclasts and osteoblasts (GPCRs) which increase cAMP
Increased cAMP causes calcium to move from the bones fluid and into cells
Osteoblasts and osteocytes have gap junctions allowing calcium to move through
the osteocytes to the osteoblasts and into the plasma
Slow Exchange
Activated by prolonged hypocalcaemia
PTH causes osteoclasts to increase bone resorption to increase calcium plasma
conc
Osteoblasts activity is inhibited
Phosphate levels are also increased
Calcium levels are restored when dietary levels increase
PTH causes cavities in bone causing weakness
PTH Effect on Kidneys
PTH promotes calcium retention so reabsorption
Promotes phosphate excretion decrease calcium reabsorption
Activates vitamin D which increase calcium absorption in the GIT
Calcitonin
Antagonist to PTH
Secreted by C cells in the thyroid
Secretion increases when calcium plasma levels are high
Acts to decrease plasma levels
Inhibits reabsorption of calcium and phosphate in the kidney
Decreases bone resorption so inhibits osteoclasts activity
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