Calcium

Question 1

State two ways in which calcium is lost from the body.

Answer 1

From the kidneys in the urine and also in the GI as it is secreted into this tract.

Question 2

How is calcium carried in the serum?

Answer 2

Some is in its biologically active form, some is bound to plasma proteins and some forms complexes with citrate.

Question 3

What are the two substances that work to increase calcium levels?

Answer 3

Parathyroid hormone and vitamin D.

Question 4

What three functions does parathyroid hormone carry out?

Answer 4

It stimulates reabsorption in the kidneys and excretion of phosphate. It also stimulates osteoclasts and stimulates hydroxylation of vitamin D into its active form.

Question 5

What is the action of Vitamin D?

Answer 5

This stimulates intestinal and renal absorption, and also increases bone reabsorption.

Question 6

When is the action of calcitonin thought to be of importance?

Answer 6

It is normally thought that the body can survive without calcitonin, but in pregnancy it may play a role in maintaining the maternal skeleton.

Question 7

What is PTH?

Answer 7

This is a polypeptide hormone, which is produced by the parathyroid gland and is cleaved in the liver after secretion.

Question 8

State two ways in which PTH is regulated.

Answer 8

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.

Question 9

Explain the effect of negative feedback on calcium levels.

Answer 9

When calcium is high, it binds to receptors on the parathyroid inhibits release of PTH.

Question 10

What is the priority of the body in terms of calcium?

Answer 10

Serum calcium is the most important thing. Sometimes at the detriment of bone in some diseases.

Question 11

What does reabsorption of bone increase in the blood plasma?

Answer 11

Both phosphate and calcium levels, as in the bone calcium is found as calcium phosphate crystals in collagen fibrils.

Question 12

What is excreted in the kidney when calcium is reabsorbed and why?

Answer 12

Phosphate. Prevents stone formation.

Question 13

What can be said about gut secretions and calcium?

Answer 13

Many gut secretions are rich in calcium.

Question 14

What is calcitrol?

Answer 14

This is the active form of vitamin D.

Question 15

Where do we source vitamin D from?

Answer 15

We obtain it from our diet and it is also produced by the action of Uv light on Cholestrol.

Question 16

What is cholecalciferol?

Answer 16

This is vitamin D3. It is hydroxylated in the liver and then the kidney to give calcitrol.

Question 17

What is the serum carrier of vitamin D3?

Answer 17

Trancalcferin.

Question 18

What is the effect of hypercalcaemia?

Answer 18

Stones, moans and groans. It can lead to kidney damage, constipation, dehydration, tiredness, depression.

Question 19

What can cause hypercalcaemia?

Answer 19

Either over secretion of PTH from a tumour or parathyroid hormone related peptide from other tumours.

Question 20

What is the initial treatment for hypercalcaemia?

Answer 20

Fluids to replace excess water lost in kidney due to calcium excretion.

Question 21

What is the effect of hypocalcaemia?

Answer 21

This leads to excitability of the Neuromuscular junctions which can lead to tremor, convulsions, pins and needles and paralysis

Question 22

What is the most common cause of hypoglycaemia?

Answer 22

Insufficient dietary intake. Serum calcium is maintained as a priority so this can leads to weak bones –> rickets in children.

Question 23

Why is PTH deficiency such a big problem?

Answer 23

This means that calcium levels are not regulated, and this leads to hypocalcaemia which is life threatening if respiratory muscles become involved in contractions.

Question 24

Where in the body is most calcium stored and what is its purpose here?

Answer 24

Skeleton. It provides structural support and acts as a calcium reserve.