L21 - calcium metabolism

Question 1

Where is most of the calcium in the body stored?

Answer 1

In the skeleton as hydroxyapatite crystals (calcium phosphate)

Question 2

Name three functions calcium has in the body.

Answer 2

Maintanence of bones and teeth/a factor in the blood clotting cascade/reduces blood pressure/ essential for muscle contraction and nerve transmission/essential for normal renal function/essential for ion movement between cells.

Question 3

What three hormones are involved in the regulation of serum calcium and phosphate levels/

Answer 3

-Parathyroid hormone/calcitriol (activated metabolite of vitamin D)/calcitonin (from parafollicular cells in thyroid gland)

Question 4

Why is phosphate important?

Answer 4

Essential for ATP and thus metabolism

Question 5

What organs does PTH act on? And what happens at each organ?

Answer 5

The bones - PTH increases bone resorption and thus the release of calcium
The intestine - activates vitamin D (to calcitriol - has a role in dietary absorption and kidney reabsorption of calcium) and thus causes an increase in Ca uptake from the intestine
Kidney - Increases reabsorption of calcium here and activation of calcitriol

Question 6

The total plasma concentration of all three forms of calcium is 2.2 - 2.7 mmol/L however the free calcium is between 1 and 3. T/F

Answer 6

T

Question 7

What activates PTH synthesis?

Answer 7

Low serum calcium

Question 8

What cell continually synthesis PTH and what organ clears it?

Answer 8

Chief cells synthesise it and degrade it. The liver is the main clearance organs

Question 9

Where do the parathyroid glands sit?

Answer 9

behind the thyroid gland, usually 4 of them.

Question 10

During thyroid surgery why do we have to be careful?

Answer 10

Can disrupt blood supply or actual parathyroid gland -> would cause a massive hypocalcaemia –> death

Question 11

There is a calcium receptor on the chief cells which is sensitive to serum calcium. If calcium levels were to rise -> ca binds the CaR. What pathway is followed to inhibit PTH secretion in response?

Answer 11

Gaq. The cells constitutively release PTH to cause calcium secretion unless the receptor causes an inhibition

Question 12

PTH increases serum calcium but what effect does it have on phosphate and why?

Answer 12

Increases loss of phosphate so kidney stones don’t form.

NOTE - PTH affects Mg too thats all we need to know though

Question 13

PTH decreases _____ activity and increases _____activity

Answer 13

osteoblast/osteoclast

Question 14

Whilst PTH manages the short term regulation of calcium homeostasis, what does the long term regulation?

Answer 14

Calcitriol (from vitamin D)

Question 15

Good dietary sources of vitamin D include meat and fish, diet is a minor source though, what is the major source?

Answer 15

The sun

Question 16

PTH causes the final hydroxylation of vitamin D to calcitriol in the kidney but vitamin D has already been modified a few times by this point, where do these initial modifications occur?

Answer 16

liver and is absorbed in the intestine

Question 17

Where is calcitionin made and released from?

Answer 17

parafollicular cells (C cells)

Question 18

What is the action of calcitonin?

Answer 18

Decreases plasma levels of calcium (doesn’t seem to be that important in humans as thyroidectomy patients seem to be fine)

Question 19

What is bad if we get excessive calcium resorption in regard to stature?

Answer 19

Loss of skeleton which can cause functional problems.

Question 20

What are the symptoms of chronic hypercalcaemia and hypocalcaemia

Answer 20

Hypercalcaemia - ‘STONES, MOANS, GROANS, BONES’
Kidney stones/bone and muscle pain/depression/also dehydration and constipation/lethargy and coma

hypocalcaemia - pins and needles, convulsions, tetany(intermittent muscular spasms)

Question 21

What can cause chronic hypercalcaemia/

Answer 21

Bone metastases (very important)/primary hyperparathyroidism (parathyroid adenoma)/ small cell carcinoma of the lung releasing parathyroif hormone related peptide/secondary hyperparathyroidism (e.g. vitamin D deficiency)

Question 22

What is the treatment for hypercalcaemia (if possible)

Answer 22

Rehydration (due to bodys attempt to correct with polyuria)

Question 23

What is the treatment for hypocalcaemia?

Answer 23

oral calcium/vitamin D supplements

Question 24

Osteoporosis does NOT increase serum calcium (lowered bone density) , in osteomalacia (rickets in children due to vitamin D deficiency) there is an undermineralisation of the bone. What are the symptoms in kids?

Answer 24

Bending of long bones

Question 25

Distinguish between primary and secondary hyperparathyroidism

Answer 25

primary - parathyroid tumour

secondary - vitamin D deficiency -> poor calcium absorption -> low serum calcium -> PTH release