Calcium Homeostasis Flashcards
(31 cards)
What are some of the roles of calcium in the body? (5)
Signalling Blood clotting Apoptosis Skeletal strength Membrane excitability
How does hypocalcaemia affect neurones?
Increases neuronal sodium permeability
Leads to hyperexcitability of neurones
Can cause tetany
How does hypercalcaemia affect neurones?
Decreases neuronal permeability
Reduces excitibility
Depresses neuromusclar activity
Can cause arhythmias
What are the calcium stores in the body? (3)
Bones (99%)
ICF - mitochondria and SR (0.9%)
ECF (0.1%)
What is the normal range of calcium in plasma?
2.2-2.6Mm
What is physiologically active calcium in the plasma?
Calcium ions that are free ionised and not bound to plasma proteins
What percentage of calcium in the plasma is bound to protein?
40%
What proteins may calcium be bound to in the blood?
Albumin
Globulin
What pH conditions increase calcium binding?
Alkalotic (can precipitate hypocalcaemic tetany)
Where is Ca2+ excreted in the body?
Faeces
Kidneys
How do osteoclasts mobilize bone?
Secrete H+ ions to dissolve calcium salts and proteolytic enzymes to digest the extracellular matrix
What are the two key enzymes that increase calcium in the plasma?
PTH
Calcitriol (active form of Vit D3)
How is calcitriol produced?
Produced from Vit D in the liver and kidneys
How many parathyroid glands do humans usually have?
4
How does PTH increase plasma calcium? (5)
Stimulate osetoclasts Inhibit osteoblasts Increase resorption of Ca2+ from kidneys Increasing renal excretion of phosphate Stimulates kidney to produce calcitriol
What hormone stimulates formation of calcitriol in lactating women?
Prolactin
What dietary sources are there for vitamin D?
Mackeral and tuna
Fish liver oils
Egg yolk
Fortified milk
What is 1,25(OH)2D3 also known as?
Calcitriol
How does PTH influence calcitriol formation?
Stimulates production of it in the kidneys
How does calcitriol increase plasma Ca2+?
Increase active transport of calcium from the gut
Facilitating renal absorption of calcium
Stimulates osteoclasts
What is classed as vitamin D deficiency?
Circulating levels fall below 20ng/ml
Which populations are most at risk of calcium and phosphate deficiency?
Elderly
Asian
Why are Asian populations are at risk of calcium deficiency?
Diet involving chapatti flour contains phytate which binds dietary calcium
Dietary deficiency of calcium
Pigmented skin less able to make vitamin D in response to UV light
What is the key hormone that decreases plasma Ca2+?
Calcitonin
