1.99 Calcium Homeostasis Flashcards
What are calcium ions essential for?
Neurotransmitter release in synapse Blood coagulation Hormonal secretion - insulin and adrenal release Enzymatic regulation - glycolysis Muscle contraction
What percentage of calcium is found in bone?
99% in bone
9g bound intracellular
2g free intracellular - needs to be low or triggers biochemical reaction
1g extracellullar
What happens when extracellular calcium falls bellow normal?
The nervous system becomes hyper excitable - because of increased permeability of neuronal membranes to Na+ - this i because calcium is required for proteins in ECm to stick together - when calcium isn’t present, they don’t stick together and allow sodium to pass
What does hyper excitability cause?
Tetanic contrations
What is Troussaeu’s sign?
Hypocalceamic tetani
Inflate BP cuff above systolic for 90s, look for carpal spasm
In what forms is extracellular calcium present?
Protein bound - albumin 90%, globulins 10%
Anion complex - bicarcbonate, citrate and phosphate
Ionised
Which calcium is filterable at the kidney?
free plus anion calcium
How much calcium is excreted daily?
Diet - 1000mg
4/5 is excreted (foecal) - 800mg
How much calcium is absorbed from our daily diet?
35%
How much is lost through GI excretion?
15%
What percentage is lost from urine from what is absorbed in the GI?
Remaining 20% is lost in the urine
How much of the calcium filtered by the kidney is excreted?
only 2% of total filtered load of the kidney is lost in the urine - out of all the calcium that is filtered through the kidney - 98% is reabsorbed
What is the rapidly exchangeable pool?
Rapidly exchangeable pool - ca that exists on the surface of the bones - doesn’t remain there for very long - moving one way or another - either from ECM into bone (formation), or from bone to ECM (remodelling)
What are the major target organs?
Intestine - absorption/secretion
Kidney - filtration/absorption
Bone - formation/resorption
what are the two absorption pathways in the intestine?
Ilieum - paracellular - passive - follows concentration gradient
Transcellular - higher up in GI - active - calcium enters down the gradient - buffered by calcium binding proteins or intracellular organelles - slowly comes off these proteins and gets pumped into the blood stream by CaATPase - against conc gradient
What are the pros and cons of active and passive processes?
Passive - no rate limiting step and is not saturable - the higher conc the faster rate of transport - if theres no gradient the passive mechanism stops
Active - It has a rate limitiing step so it is saturable - the pump is the rate limiting step, cant go faster no matter how much calcium there is - however the advantage is that there will always be gradient from gi tract into the cells so it will never stop -
What can regulate the transcellular absorption of calcium in the gut?
it can be regulated by hormones - vitamin D metabolites increase CaBP
What percentage of total plasma calcium enters the kidney?
60% of total plasma calcium
How is calcium absorbed in the kidney?
Transcellular the same was GI
30% absorbed through a passive process
Which is the most important site of reabsorption in kidney?
The most important site of reabsorption is the distal tubule - because it can be regulated by the hormones
PTH and vitamin D metabolites
In what form is calcium found in the bone?
Most is found in hydroxyapatite crystals - Ca10(PO4)6(OH)2
What percentage of calcium can be released from the bone?
Very little Ca2+ (
What does it mean by “bone is a dynamic tissue?
Bone is dynamic tissue. It is continually being formed and resorped - this is termed remodeling. 10-15% of total adult bone mass turns over each year during remodeling process
During growth, what happens to the bone remodelling process?
During growth, the rate of bone formation exceeds resorption and skeletal mass increases
