calcium and phosphate regulation

Question 1

overview of calcium regulation DIAGRAM

Answer 1

PTH and VIT D- PTH secreted by parathyroid gland embedded in thyroid- causes reabsorption from BONE and reabsorption of KIDNEY vit D causes LIVER to produce inactive form of it (calcidiol)- PTH then causes KIDNEY to produce active form called calcitriol (1,25OH2), which causes reabosorption via SMALL INTESTINE

Question 2

overview phosphate regulation DIAGRAM

Answer 2

Na/PO4 transporter on apical membrane of proximal tubular cell allows PO4 into cell from urine, then into blood PTH INHIBITS this transporter, as well as FGF23 from osteocytes- FGF23 also inhibits CALCITRIOL= less phosphate reabsorption from gut (vit D needed for phosphate reabsorption)

Question 3

regulation of PTH secretion

Answer 3

high Ca2+ in ECF binds to receptor in PTH cell, inhibiting PTH secretion- low does opposite

Question 4

VIT D production and effects, and control DIAGRAM

Answer 4

vit D from diet (ergocalciferol) converted to inactive form (25 OH D3) in liver via hydroxylation- OR skin converts 7-dehydrocholesterol into Vit D3 using sun, which is converted into inactive form via liver to become active, 2nd hydroxylation step in kidney required- PTH stimulates 1alpha-hydroxylase to do this to produce calcitiriol, causing Ca2+ absorption in gut, but also bone and kidney- then has -feedback on PTH

Question 5

causes of vit D deficiency DIAGRAM

Answer 5

using pathway- lack of UV light, dietary issues/malabsorption eg coeliac, liver disease, renal disease, and vit D receptor defects

Question 6

how calcium affects nerve/skeletal muscle excitability

Answer 6

high calcium (hypercalcaemia) competes with Na+, blocking influx= LOW excitability low calcium does the opposite

Question 7

symptoms of hypocalcaemia

Answer 7

parasthesia, convulsions (seizures), arrhythmias (heart needs calcium) and tetany

Question 8

clinical signs of hypocalcaemia

Answer 8

CHVOSTEK’S sign- tap facial nerve just below zygomatic arch (cheek bone)- causes twitching of facial muscles TROUSSEAUS sign- inflate BP cuff for few minutes= carpopedal spasm (of hand)

Question 9

causes of hypocalcaemia

Answer 9

vit D deficiency, low PTH (neck surgery as thyroid damage, autoimmune or Mg 2+ deficiency, as needed to make PTH), PTH resistance (pseudohypoparathyroidism), and renal disease

Question 10

effects of hypercalcaemia,

Answer 10

STONES, ABDOMINAL MOANS AND PSYCHIC GROANS kidney- absorbing too much Ca2+ which can deposit to form stones= renal colic GI- less muscle contraction= constipation, nausea+ anorexia CNS- fatigue, depression, coma

Question 11

causes of hypercalcaemia

Answer 11

primary hyperparathyroidism malignancy- eg ectopic PTH conditions with high bone turnover eg Paget’s disease of bone vitamin D excess

Question 12

diagnostic approach to hypercalcaemia- hyperparathyroidism

Answer 12

if Ca2+ high, should do -feedback to PTH, but if PTH high as well eg due to tumour in PTH gland, indicates primary hyperthyroidism as no feedback- thus high Ca2+, low PO and high PTH

Question 13

diagnostic approach to hypercalcaemia- hypercalcaemia of malignancy

Answer 13

Ca2+ high again, and no problem with PTH gland, so PTH low= cancer somewhere else

Question 14

vit D deficiency- define, and effects

Answer 14

lack of mineralisation in bone= bone softening, pain and proximal myopathy (rickets in kids, osteomalacia in adults)

Question 15

treatment of primary hyperparathyroidism

Answer 15

remove PTH gland

Question 16

secondary hyperparathyroidism

Answer 16

unlike primary, Ca2+ low due to VIT D DEFICIENCY, hence PTH increases to try and counteract this

often due to poor renal function

Question 17

levels of different things during VIT D deficiency

Answer 17

plasma 25(OH)D3 low (active form not measured as difficult) Ca2+ low, PO43- low (less gut absorption), and PTH high

Question 18

treatment of vit D deficiency

Answer 18

with normal renal function- 25(OH)D3 (cholecalciferol) or ergocalciferol renal failure- no point giving inactive form, so, active form of vit D (ALFACALCIDOL)

Question 19

vit D excess

Answer 19

can occur due to excess treatment or GRANULOMATOUS disease= hypercalcaemia