Calcium homeostasis Flashcards
(29 cards)
Where is calcium found?
Mostly in the skeleton and teeth. Also in the cells and a very small amount in the extracellular fluid
what form is calcium in the Skelton in
IN the form of hydroxyapatite which is crystallised calcium phosphate salt known as bone mineral
What is calcium in cells used for
a cofactor in enzyme reactions
calcium in extracellular fluid
only 50% in free biologically active form . 41% protein bound calcium can’t diffuse across capillary membranes
What is the role of calcium in bones
to provide structural strength and make bones hard
What is the role of calcium in the nervous system
release of neurotransmitters from presynaptic Nerone at neuromuscular junctions triggered by calcium ions
what is the role of calcium in the endocrine system
movement of calcium to endocrine cells triggers release of hydrophilic hormones such as adrenaline
what is the role of calcium in the blood
calcium is a cofactor in blood clotting
What is the role of calcium in intracellular processes
calcium functions as a second messenger in cell signalling pathways and as a cofactor for enzyme function in chemical reactions
How do bones regulate calcium levels
bone acts as a sink for buffering ECF calcium concentration as well as calcium in bones providing internal structural rigidity needed for locomotion
What happens if there is a decrease in calcium reserve in bones
leads to a decrease in bone strength
Where is the parathyroid hormone produced
by the parathyroid gland
How does the parathyroid hormone regulate calcium levels.
main response to too low calcium levels is to promote the transfer of calcium ions from bone fluid into plasma
What does the parathyroid hormone do in chronic hypocalcaemia
stimulates dissolution of bone
what does the parathyroid hormone do
causes rapid release of calcium from bone fluid into plasma
What is the 6 steps for the mechanism of parathyroid hormone
- PTH binds to PTH receptor on osteoblasts
- Osteoblasts secrete RANKL
- RANKL binds to RANKL receptor on osteoclast
- Osteoclast stimulated to gobble bone and release calcium and phosphate ions
- PTH stimulates cells of DCT of kidney to reabsorb calcium ions during urine formation
- This distorts the ratio of calcium and phosphate ions in the blood and prevents recrystallisation of hydroxyapatite crystals
What enzyme does PTH Target
1 alpha hydroxylase which coverts calcidiol to calcitriol
What does calcitriol do
stimulate Gi tract to absorb calcium and phosphates and PCT to reabsorb calcium ions from urine
what is vitamin d
a hormone initially synthised from cholesterol in skin keratinocytes exposed to UVB radiation
what is vitamin d converted to in the liver
calcidiol
what is calcidiol converter to in the kidney
calcitriol
what does active calcitriol do
increases the absorption of calcium into plasma in the intestine
what does calcitonin do
1) it protects against hypercalceimia by opposing actions of PTH when calcium ion concentration levels become too high
2) inhibits the activity of osteoclasts in bone
what hormones increase calcium ion concentration in blood plasma
PTH and vitamin D
