Lecture 20- Parathyroid And Calcium Regulation

Question 1

What are serum calcium levels?

Answer 1

2.2-2.6mM

ECF calcium accounts for very small amount of bodies calcium. Vast majority is in bone

Question 2

Role of calcium?

Answer 2

Blood clotting 
Bone and teeth structure 
Regulates heart rhythm 
Intracellular signalling 
Nerve transmission at neuromuscular junction

Question 3

Why need to give calcium infusion with big blood transfusion?

Answer 3

Citrate in blood transfusion chelates calcium ions

Question 4

Hormones involved in calcium and phosphate regulation and where are they made?

Answer 4

Parathyroid hormone(chief cells) and calcitriol (active form of vit D made in kidneys) raise calcium levels

Calcitonin (parafollicular cells of thyroid gland) lowers it

Question 5

When does parathyroid hormone need to be carefully monitored?

Answer 5

After neck or thyroid surgery. Decrease in parathyroid hormone will cause hypocalcaemia quickly

Question 6

PTH target organs?

Answer 6

Bone- calcium and phosphate release

Gut- increased calcium absorption

Kidneys- decrease loss to urine

Question 7

How does PTH increase gut calcium absorption?

Answer 7

Activates vitamin D which increases calcium uptake transcellularly

Question 8

Vitamin D and calcium?

Answer 8

Got mainly through sunlight and some through diet. Converted by kidneys to calcitriol which acts like a hormone on kidneys, bone and gut

Question 9

Feedback regulation of serum calcium?

Answer 9

Highplasma calcium results in decreased PTH secretion.

This leads to less calcitriol produced by kidneys and so less calcium absorbed from gut. Kidney also reabsorbs less calcium and bone building is increased while breakdown is reduced

Question 10

Hypercalcaemia?

Answer 10

High calcium makes depolarisation more difficult.

Get renal calculi
Kidney damage 
Dehydration
Constipation 
Tiredness and depression
“Stones, moans and groans”

Question 11

Hypocalcaemia?

Answer 11

Makes depolarisation easier.

Get hyperexcitability 
Pins and needles 
Tetany
Paralysis 
Convulsions

Question 12

Bone metastasis?

Answer 12

Commonly found in pelvis, ribs, skull etc and can cause calcium loss from bone

Question 13

Possible cause of hypercalcaemia?

Answer 13

Osteolytic bone metastasis

Question 14

Hyperparathyroidism?

Answer 14

Primary- adenoma in a parathyroid gland causes increased PTH

Secondary- all 4 become hyperplastic in response to vitamin D deficiency

Question 15

Effect of calcium on neuronal activity?

Answer 15

Raises threshold for nerve membrane depolarisation and so the development of an action potential

Hypercalcaemia suppresses neuronal activity while hypocalcaemia promotes it

Question 16

Severe hypercalcaemia?

Answer 16

Lethargy
Weakness 
Confusion
Coma 
Renal failure 

Treat with rehydration

Question 17

Hypocalcaemia?

Answer 17

Mainly in thyroidectomy patients

Can cause tingling, tetany of muscles and carpopedal spasm

Question 18

What causes osteomalacia or rickets in children?

Answer 18

Vitamins D deficiency

Question 19

Parathyroid hormone vs calcitriol?

Answer 19

Parathyroid generally increases calcium and decreased phosphate while calcitriol increases both and calcitonin reduces both

PTH has no direct effect on GI tract but does indirectly through causing vit D to be activated to calcitriol which does have an effect