Endocrine Control Of Calcium

Question 1

Intracellular functions of calcium

Answer 1

second messenger in signal
transduction
exocytosis (of neurotransmitters,
hormones etc.)
endocytosis
mitosis, cell division
muscle fibre contraction
fertilisation
intracellular release stores (ER,
mitochondrion)
cytosolic [Ca2+]: 10-7 M (basic);
10-5 M (stimulated)

Question 2

Extracellular functions of calcium

Answer 2

bone and teeth formation as
(Ca5(PO4)3OH = Hydroxyapatite
Blood clotting
extracellular ionised [Ca2+] tightly
regulated: ~ 2.1 – 2.6 x 10-3 M
plasma [Ca2+] and [Pi] are regulated in a coordinated way through the same hormones.

Question 3

Where is most of the body’s calcium found?

Answer 3

In bones and teeth in an inorganic complex
99% of the body’s calcium

Question 4

3 major hormones involved in precise endocrine calcium regulation

Answer 4

Parathyroid hormone (PTH)
Vitamin D3 (calcitriol)
Calcitonin

Question 5

3 major organ targets for the calcium regulation hormones

Answer 5

Bone
Kidney
Intestine

Question 6

PTH

Answer 6

– peptide hormone from Parathyroid glands
acts to sustain plasma Ca2+ levels by stimulating
1) mobilisation of Ca2+ from bone 2) re-absorption of Ca2+ from kidney 3) production
of an active vitamin D3 metabolite.

Question 7

Parathyroid glands

Answer 7

4 small glands at the back of the thyroid
Produce PTH
Very important for sensing plasma calcium levels

Question 8

Vitamin D3 (cholecalciferol)

Answer 8

cholesterol (steroid) derivative.
taken up through diet or converted from precursor by UV light, and hydroxylated in liver
and kidney to active form (1,25 dihydroxycholecalciferol = calcitriol).
Acts on bone to mobilize calcium, and stimulates absorption of Ca2+ from gut lumen.

Question 9

Calcitonin

Answer 9

peptide hormone from thyroid C-cells.
lowers plasma Ca2+ by inhibiting mobilization from bone.
minor role in adults, but may protect maternal skeleton from Ca2+ resorption during
pregnancy & lactation.