26 - Calcium

Question 1

Hypocalcinaemia

Answer 1

Causes irritable nerves

Question 2

Why tachyarrhythmia in hypocalcinaemia

Answer 2

o Calcium stabilises Na+ channels so if not enough = reduces threshold for AP to fire –> tetany, tachyarrhythmias

Question 3

Which cells in parathyroid gland secrete PTH

Answer 3

Chief cells

Question 4

What dye do oxyphils take up

Answer 4

technetium

Question 5

Effects of PTH

Answer 5

o BONE: PTH enhances Ca release from bones + phosphate ( don’t need more phosphate hence excreted by kidney)
o INTESTINE: Enhances the absorption of calcium and phosphate from the small intestine by activating 1,25D (calcitriol)
o KIDNEY: Decreases calcium excretion in urine and increases phosphate excretion in urine

Question 6

Formation of pth

Answer 6

polypeptide prohormone preproPTH (RER) → proPTH (Golgi)→ PTH (Vesicles)

Question 7

When is PTH released

Answer 7

When low serum calcium

Question 8

o PTH 1-84 has a circulation life

Answer 8

2 minutes

Question 9

Calcium sensing receptor

Answer 9

o GPCR – reduces PTH secretion → increases breakdown of stored PTH
 Supresses transcription of PTH gene
 Restrains PTH proliferation

Question 10

Familial hypocalciuric hypercalcemia (FHH)

Answer 10

Changes set point of calcium

Question 11

Calcitriol on PTH

Answer 11

Suppresses PTH gene transcription

Question 12

Phosphate on PTH

Answer 12

Stimulates PTH gene transcription

Question 13

Cinacalcet

Answer 13

activates the CASR and reduces calcium levels

Question 14

Reabsorption in proximal tube

Answer 14

65% reabsorption – PTH independent (voltage gradient)

Question 15

Reabsorption in loop of henle

Answer 15

% reabsorption – PTH independent - Loop diuretics inhibit- CASR downregulates Na/K/2Cl

Question 16

Reabsorption in distal tubule

Answer 16

10% reabsorption – PTH upregulates Ca channels, calcium ATPase and Na/Ca exchanger, TPRV

Question 17

Other renal PTH effects

Answer 17

o Down-regulation of NaPi transporters - Reduced phosphate reabsorption
o Vitamin D Activation
 Stimulation of 25(OH) D3 –> 1,25(OH)2 D3

Question 18

Function of opg

Answer 18

inhibits osteoclastogenesis

Question 19

Bone made of

Answer 19

Collagen + Hydroxyapatite

when mineralised = + Phosphate and alkaline phosphate

Question 20

What can inactivate vitamin D

Answer 20

hydroxylated at the 24

Question 21

Vitamin D receptor

Answer 21

o Nuclear and membrane bound

o VDR inihibits 1 α hydroxylase (negative feedback)

Question 22

FGF 23

Answer 22

hormone that reduces serum phosphate
o Activating mutation in FGF23 - Autosomal dominant hypophosphataemic rickets
o Tumour induced osteomalacia - paraneoplastic FGF23
o Familial tumoral calcinosis - low levels FGF23

Question 23

Calcitonin prodiced

Answer 23

Thyroid C cells

Question 24

Primary hyperparathyroidism

Answer 24

o Rugger Jersey Spine
o Terminal Tuft Erosion
o Brown tumour

Question 25

What causes primary hyperparathyroidism

Answer 25

Parathyroid tumour

Question 26

Primary hypercalcaemia

Answer 26

o	Kidney stones
o	Osteoporosis
o	Mood disorder – depression
o	Diabetes- Polyuria and polydipsia
o	MIBI SCAN

Question 27

Hypocalcaemia symptoms

Answer 27

o Convulsions
o Arrhythmia
o Tetany
o Kidney stones (both hyper and hypo)

Question 28

Tx of hypocalcaemia

Answer 28

IV oral calcium
chronic - alfacalcidol (1,25 vitamin D3) orally – increase gut absorption of Ca but lack of PTH means Ca will be lost from kidneys at a high rate