Calcium Flashcards
State two ways in which calcium is lost from the body.
From the kidneys in the urine and also in the GI as it is secreted into this tract.
How is calcium carried in the serum?
Some is in its biologically active form, some is bound to plasma proteins and some forms complexes with citrate.
What are the two substances that work to increase calcium levels?
Parathyroid hormone and vitamin D.
What three functions does parathyroid hormone carry out?
It stimulates reabsorption in the kidneys and excretion of phosphate. It also stimulates osteoclasts and stimulates hydroxylation of vitamin D into its active form.
What is the action of Vitamin D?
This stimulates intestinal and renal absorption, and also increases bone reabsorption.
When is the action of calcitonin thought to be of importance?
It is normally thought that the body can survive without calcitonin, but in pregnancy it may play a role in maintaining the maternal skeleton.
What is PTH?
This is a polypeptide hormone, which is produced by the parathyroid gland and is cleaved in the liver after secretion.
State two ways in which PTH is regulated.
Transcriptional level - low calcium increases transcription, high calcium reduces. It is also controlled by an unknown mechanism post transcriptionally where low calcium leads to prolonged survival of mRNA.
Explain the effect of negative feedback on calcium levels.
When calcium is high, it binds to receptors on the parathyroid inhibits release of PTH.
What is the priority of the body in terms of calcium?
Serum calcium is the most important thing. Sometimes at the detriment of bone in some diseases.
What does reabsorption of bone increase in the blood plasma?
Both phosphate and calcium levels, as in the bone calcium is found as calcium phosphate crystals in collagen fibrils.
What is excreted in the kidney when calcium is reabsorbed and why?
Phosphate. Prevents stone formation.
What can be said about gut secretions and calcium?
Many gut secretions are rich in calcium.
What is calcitrol?
This is the active form of vitamin D.
Where do we source vitamin D from?
We obtain it from our diet and it is also produced by the action of Uv light on Cholestrol.
What is cholecalciferol?
This is vitamin D3. It is hydroxylated in the liver and then the kidney to give calcitrol.
What is the serum carrier of vitamin D3?
Trancalcferin.
What is the effect of hypercalcaemia?
Stones, moans and groans. It can lead to kidney damage, constipation, dehydration, tiredness, depression.
What can cause hypercalcaemia?
Either over secretion of PTH from a tumour or parathyroid hormone related peptide from other tumours.
What is the initial treatment for hypercalcaemia?
Fluids to replace excess water lost in kidney due to calcium excretion.
What is the effect of hypocalcaemia?
This leads to excitability of the Neuromuscular junctions which can lead to tremor, convulsions, pins and needles and paralysis
What is the most common cause of hypoglycaemia?
Insufficient dietary intake. Serum calcium is maintained as a priority so this can leads to weak bones –> rickets in children.
Why is PTH deficiency such a big problem?
This means that calcium levels are not regulated, and this leads to hypocalcaemia which is life threatening if respiratory muscles become involved in contractions.
Where in the body is most calcium stored and what is its purpose here?
Skeleton. It provides structural support and acts as a calcium reserve.
