Physiology of Bone and Calcium Homeostasis Flashcards
What is hydroxyapatite?
the calcium phosphate which preciptates to the collagen matrix to make bone
What are the two types of bone?
trabecular bone and compact bone
What is the role of osteoblasts?
to build bone by producing collagen, proteins and enzymes
How do bones grow in length?
at the epiphyseal plate chondrocytes divide and then disintegrate leaving a space for osteoblasts to synthesise bone
What type of cell are osteoblasts like?
fibroblasts
Where are osteoclasts derived from?
haematopoetic stem cells
What is the function of osteoclasts?
secretes acid and proteases to dissolve the calcium and collagen matrix of bone
What are the roles of calcium?
intracellular signalling, bone matrix, tight junctions, cofactor in coagulation, neuron and muscle excitability
Which organs are involved in calcium homeostasis?
bone, kidney and intestine
What is the concentration of calcium in the ECF?
2.5mM
What is the concentration of calcium in the ICF?
0.001mM
What is the role of PTH?
calcium and phosphate release from bone, increases calcium reabsorption in the kidney, decreases phosphate reabsorption in the kidney, activates vitamin D hydroxylation in the kidney
What stimulates PTH release?
low plasma calcium
What is the chemical nature of PTH?
peptide
What is the role of calcitonin?
decreases bone resorption and increases calcium excretion in the kidney
What stimulates the release of calcitonin?
high plasma calcium - is not released in normal physiology
Where is calcitonin released from?
C cells of the thymus
What is the chemical nature of calcitonin?
peptide
What steps are required to activate vitamin D?
sunlight in the skin, hydroxylation in the liver and hydroxylation in the kidney
What stimulates hydroxylation of vitamin D in the kidney?
PTH and high plasma phosphate
What is calcitriol?
1,25-dihydroxycholecalciferol (activated vitamin D3)
What are the roles of phosphate?
energy transfer and storage (ATP, cAMP), control of enzymes, transporters and ion channels, DNA and RNA
How are calcium and phosphate related?
calcium and phosphate need to be controlled in the blood because if both their levels are high they will precipitate - this is maintained by PTH opposing their reabsorption and excretion in the kidney
What causes hyperparathyroidism?
tumour
What causes hypoparathyroidism?
autoimmune attack of parathyroid glands or surgical ressection
What are the symptoms of hypoparathyroidism?
hypocalcaemia and hyperphosphataemia, neuromuscular excitability - fatal
What are the symptoms of vitamin D deficiency?
rickets in children and osteomalacia in adults
