Calcium Homeostasis Flashcards
What are the 5 roles of calcium in the body?
Signalling - exocytosis of synaptic vesicles in the body Blood clotting Apoptosis Skeletal strength Membrane excitability
What is the consequence of hypocalcaemia?
Increase the neuronal sodium permeability increasing excitation and can cause tetany
What is the outcome of hypercalcaemia?
Decrease neuronal sodium permeability and decrease neuromuslcar activity leading to cardiac arrhythmias
What 3 compartments of the body is calcium stored within?
The extracellular matrix of the bones -99%
Intracellular fluid -0.9%
The extracellular fluid 0.1%
How is calcium stored within the bones?
As hydroxyapatite crystals
What element other than calcium does hydroxyapatite contain and why is this important?
Phosphorus, important role in calcium homeostasis because without it calcium cannot be laid down in the bones
What is the calcium contained within in the ICF?
Mitochondria and sarcoplasmic reticulum
What percentage overall is free calcium?
0.05% and this is all that is physiologically active
In what state is calcium in the extracellular fluid?
40% bound to carrier proteins
50% free, ionised and physiologically active
10% are bound to plasma anions forming complexes
What two protein carriers hold calcium?
Albumin - 80%
Globulin - 20%
What increases the binding capacity of calcium to carrier proteins
An increased pH, alkaline environments
When would we be able to create an alkaline environment in the body?
Hyperventilation
What acts as a reservoir for plasma calcium?
Bones
What cells form bone?
Osteoblasts
What cells degrade bone?
Osteoclasts
What two hormones increase calcium concentration in the blood?
Parathyroid hormone and calcitriol
What causes a release of PTH?
Decreased calcium concentration in the blood
What mechanisms does PTH to restore plasma calcium?
Inhibits osteoblasts to reduce bone formation
Stimulating osteoclasts to increase resorption
Increasing reabsorption of Ca2+ from the kidney tubule
Increasing renal excretion of phosphate. This elevates free [Ca2+ ] by preventing it from being deposited back into bone
timulates the kidney to synthesise calcitriol
What are the 2 alternative names fro calcitriol?
Vitamin D or 1,25 dihydroxycholecalciferol
What type of hormone is calcitriol?
Steroid hormone
What is calcitriol’s main function?
Increase calcium absorption in the gut
What is the classification of a vitamin D deficiency?
Levels less than 20ng/ml
What can vitamin D deficiency lead to?
Rickets in children and
Osteomalacia in adults
What is the effect of cortisol on osteoblasts?
Decreases plasma calcium levels
