calcium homeostasis Flashcards
how much calcium is ionised in the body
60%
how much calcium in body
1kg
99 % in bone
how much calcium intracellular
100nM basal
what is calcium involved in
intracellular signalling
where is calcium stored in cells
ER or ribosomes
calcium in response to electrical signal
in muscles
calcium’s released from the sarcoplasmic reticulum to lead to muscle contraction via tin and myosin
symptoms if calcium is not balanced
reduced blood flow
neuromuscular irritability
hypocalceamia causes Na influx
tetanic contraction
recommended calcium intake
700mg per day
children more due to laying down of bone
uptake oc calcium routes
transcellular
paracellular
transcellular uptake
low intake
active transport
required binding of proteins, use of aTP to transport small amounts of Ca2+
paracellular
high intake
passive
i.e. high intake from gut into cells
homeostasis
- high calcium levels may lead to excretion via the kidney, most calcium is reabsorbed though
- bone is a major reservoir for calcium
- needs to be net mineralisation for bone growth to occur
what has an influence on calcium
parathyroid and thyroid
Vit D
what do parathyroid and thyroid do
regulate homeostatic calcium elvesl
paththyroud secretes parathyroid hormone
thryoid releases calcitonin
parathyroid hormone
medium size peptide chain (84aa peptide)
- Ca2+ inhibits release
- low levels the hormone is released, causing breakdown of bone (osteolytic osteolysis) by osteoclasts
- causes increased synthesis of Vit D formation in kidney
calcitonin released by
parafollicular cells
calcitonin
- 32 aa peptide
- released when calcium levels are too high
- inhibits bone resorption
- stops calcium being removed from bone into the plasma
- may not really have a role in normal homeostasis, unknown
Vit D
Allows SL absorption
- has to be hydroxylated 2 sides to make it an active hormone (1 AND 25 SIDE)
- upregulates carriers
- changes junctions (makes them more permeable to calcium)
how can we synthesise Vit D
- can be formed from cholesterol
- therefore Vit D might not be considered a vitamin
- the receptor is a transcription factor, therefore can cause the activation and down regulation of other genes
- UV light allows us to synthesise vit D
what does Vit D affect development and how
receptors present in developing bone
insufficient calcium prevents sufficient mineralisation of the bone
Vit D and teeth
insufficient Vit D enamel hypoplasia enlarged pulp horns elayed eruption caries risk
prevention
- vit D and fluoride)
how does Vit D affect burn turonver
Vit D able to ascite osteocalsts
increase plasma calcium levels
Vit D act indirectly with osteoblasts
osteoblasts release RANK ligand
non skeletal roles of calcium
- cancer
- autoimmune disease
- hypertension and CVS disease
- diabetes
- muscle strength
- schizophrenia and depression
osteomalacia and consequnces
lack of remineralisation
- pathological amount of callus matrix
- pseudo fractures
- bone pain
- muscle weakness
- periodontitis
osteoporisis
low bone density in adults
what is used to assess bone density
T score
0 is normal
lower the score lower the density
pathogenesis of osteoporiris
reduced uptake of dietary calcium
imbalance of bone turnover
reduced bone density
oestrogen in signalling (osteoporosis)
reduced inhibiton of osteoclasts
therefore bone broken down more
prevention/treatment of osteoporosis
calcium and vit D tablets
alendrotnic acid can be prescribed (blocks osteoclast acvitivty)
weight bearing activity
Vit D supplement amount
1000 IU/day
