Calcium Flashcards
What are the main functions of calcium?
builds and maintains bones and teeth
helps regulate passage of nutrients
assists in normal blood clotting
helps maintain proper nerve and muscle function
needed for intracellular signalling pathways
appropriate levels needed for nerve transmission
How is calcium stored in bone?
Hydroxyapatite crystals
Why don’t we want high levels of calcium and phosphate in the blood?
Crystals may form in the blood
What are the effects of PTH?
stimulates bone resorption and release of calcium
stimulates calcium reabsorption in kidney
increased excretion of phosphate
activates vitamin D by hydroxylation
What are the effects of dietary vitamin D?
increases intestinal absorption of calcium
increases renal reabsorption of calcium
increases bone resorption
What does calcitonin do?
Counteracts the effects of PTH to decrease serum calcium levels
Where is calcitonin released?
C cells in the thyroid gland
How many parathyroid glands are there?
4
Which cells secrete PTH?
Chief cells of the parathyroid gland
What type of hormone is PTH?
Peptide
How does low serum calcium affect the chief cells?
up-regulation of transcription of PTH
prolonged survival of PTH mRNA
Where is PTH degraded?
released PTH is degraded in the liver
non-released PTH is degraded in the chief cells
What kind of receptor is the calcium receptor on the chief cells?
G protein
How does increased serum calcium reduce PTH release?
binds to receptors
inhibits adenylate cyclase
reduced cAMP
reduced PTH release
When PTH release is decreased, is it due to increased degradation or decreased synthesis?
Increased degradation
How would high phosphate levels affect PTH secretion?
Increased PTH secretion
High would high magnesium levels affect PTH secretion?
decreased PTH secretion
How do osteoblasts work?
They produce collagen matrix which is mineralised by hydroxyapatite.
How do osteoclasts work?
They produce an acidic micro-environment which dissolves hydroxyapatite.
How does PTH increase bone resorption?
cytokines released
stimulates osteoclasts activity and reduces osteoblast activity
resorption of mineralised bone occurs
Where is calcium reabsorbed in the kidneys?
ascending limb
DCT
Where is the greatest uptake of calcium?
Duodenum and jejunum
Does the uptake of calcium require energy?
Yes
How is vitamin D made in the skin?
through the action of sunlight on cholesterol
What are the 2 forms of vitamin D and where do they come from?
D3 - made in skin and from dairy
D2 - from yeast and fungi
Which form of vitamin D is added to margarines?
D2
What does vitamin D form when activated?
calcitriol
How many hydroxylation reactions does it take to activate vitamin D and where do they occur?
2 hydroxylation reactions
first reaction = liver
second reaction = kidney
What is the half-life of calcitriol?
1/4 day
Which enzyme is required for hydroxylation of vitamin D?
1 alpha-hydroxylase
How does calcitriol work to increase calcium uptake in the gut?
Increases the sensitivity of microvilli calcium channels in the gut
What are the signs of hypocalcaemia?
pins and needles
paralysis
tetany (spasms)
convulsions
What are the signs of chronic hypercalcaemia?
renal stones kidney damage constipation dehydration tiredness depression
What is the treatment for hypercalcaemia?
fluids
check for tumour causing over-secretion of PTH
Where would PTH related peptide be released from?
Tumours in other places around the body
What would primary hyperparathyroidism be caused by?
A parathyroid adenoma
What is rickets?
a disease in children
long bone has failed to mineralise due to calcium/vitamin D deficiency
How does vitamin D regulate phosphate levels?
Stimulates the uptake of phosphate in the gut
How can calcium travel in theblood?
free calcium
bound to plasma proteins
complexed with citrate
