Calcium and the Bone

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Calcium
A mineral needed to make up bones, teeth and connective tissue. It's also used in blood clotting, as a second messenger, muscle contraction and in nerve transmission at neuromuscular junctions
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Hydroxyapetite
Crystals of bound calcium and phosphate that make up most of the body's supply
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Parathyroid
Four glands embedded in the posterior side of the thyroid which release PTH. They are essential for life
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Chief cells
Cells of the parathyroid that contain calcium-sensing G-protein coupled receptors. They are switched off at high levels of calcium and become active when there is less calcium interacting with the receptors, causing released of pre-stored PTH
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Rapid mobilisation
PTH acts on the osteocyte membrane, making it more leaky towards calcium phosphate so that more can be released into the blood
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Slow mobilisation
PTH binds to osteoblasts, releasing RANK-L which stimulates differentiation of osteoclasts. Osteoclasts destroy bone collagen, releasing hydroxyproline as a biomarker
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Kidney
The organ where PTH blocks the sodium-phosphate cotransporter, preventing uptake of phosphate in the PCT. PTH increases Ca2+ATPase activity, increasing Ca2+ uptake in the DCT
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Photolysis
UV-dependent reaction that converts 7-dehydrocholesterol to cholecalciferol on the skin
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Liver
The organ where cholecalciferol is transported to and converted to 25(OH)2D3
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Kidney
The organ where 25(OH)2D3 is converted to 1,25(OH)2D3 in the PCT by 1 alpha hydroxylase (PTH increases expression of this enzyme)
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Vitamin D
1,25(OH)2D3 - a vitamin which increases calcium and phosphate absorption, increases synthesis of calbindin in intestinal cells, facilitates remodelling of bone. It acts on nuclear receptors
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Calcitonin
Hormone secreted by parafollicular cells which decrease calcium levels by binding to osteoblasts to increase bone formation
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Hypercalcaemia
A disorder where a malignant tumour produces excess PTH, causing kidney stones, constipation, dehydration, tiredness and depression. Reverse with parathyroidectomy
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Hypocalcaemia
A disorder due to vitamin D deficiency, PTH deficiency or renal disease. This causes numbness, muscle cramps and wheezing. Treat with vitamin D replacement therapy
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Osteomalacia
(Rickets in children). A disorder due to vitamin D deficiency as a result of poor diet, lack of sunlight or renal failure. It causes bowing of legs, muscle weakness and bone fractures. Treat with vitamin D replacement therapy
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Osteoclasts
Bone resorption cells. Their differentiation is stimulated by the release of RANK-L from osteoblasts. It sits on and seals off bone, secretes H+ and phosphotases to create an acidic environment to break apart mineralised collagen
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Osteoblasts
Bone forming cells - they are precursors of bone lining cells and osteocytes, and they regulate osteoclast differentiation. Differentiated from mesenchymal cells
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Bone lining cells
Specialist inactive osteoblasts involved in the initiation of bone remodelling
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Osteocytes
Cells involved in mechanosensing microfractures in the bone. They stimulate osteoblast differentiation
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OPG
A dummy receptor found on osteoclasts alongside RANK receptors. It blocks osteoclast differentiation
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Osteopetrosis
A disease caused by a decrease in bone resorption leading to very dense but fragile bone. It may be due to overexpression of OPG, less RANK, less RANK-L
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Osteoporosis
A disease caused by a massive increase in bone resorption leading to fragility due to loss of bone density. It may be due to absence of OPG, overexpression of RANK-L
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Oestrogen
A decrease in this hormone in post-menopausal women leads to an increase in RANK-L production. This overwhelms the OPG dummy receptors, activating more osteoclasts, causing more bone resorption, leading to a loss of bone density (osteoporosis)
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Other cards in this set

Card 2

Front

Crystals of bound calcium and phosphate that make up most of the body's supply

Back

Hydroxyapetite

Card 3

Front

Four glands embedded in the posterior side of the thyroid which release PTH. They are essential for life

Back

Preview of the back of card 3

Card 4

Front

Cells of the parathyroid that contain calcium-sensing G-protein coupled receptors. They are switched off at high levels of calcium and become active when there is less calcium interacting with the receptors, causing released of pre-stored PTH

Back

Preview of the back of card 4

Card 5

Front

PTH acts on the osteocyte membrane, making it more leaky towards calcium phosphate so that more can be released into the blood

Back

Preview of the back of card 5
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