calcium metabolism

Question 1

roles of calcium

Answer 1

neuromuscular excitability, muscle contraction, strength in bones, intracellular second messenger, intracellular co-factor, hormone/neurotransmitter stimulus-secretion coupling, blood coagulation (factor IV)

Question 2

calcium presence in body

Answer 2

most as calcium salts; mainly found in bone as completed hydrated calcium salt; in blood, some present as ionised Ca2+, some bound to protein and some left as soluble salts

Question 3

which type of calcium is bioactive

Answer 3

free (unbound) Ca2+

Question 4

calcium in blood

Answer 4

50% unbound is ionised and 45% bound to plasma proteins (5% as diffusible salts)

Question 5

calcium handling by the body: intake, absorbance, use and excretion

Answer 5

intake via GIT (to faeces) → absorbed in bloodstream (invisible loss to dead cells, hair, nails) → balance with bone and all cells → kidneys and urine

Question 6

define hypocalcaemia

Answer 6

low blood [Ca2+]

Question 7

what does hypocalcaemia cause

Answer 7

tetany (intermittent muscular spasms)

Question 8

what two signs are associated with hypocalcaemia

Answer 8

Trousseau’s sign and Chvostek’s sign

Question 9

what is Trousseau’s sign

Answer 9

carpopedal spasm

Question 10

what is Chvostek’s sign

Answer 10

facial spasm

Question 11

endocrine causes of hypocalcaemia

Answer 11

hypoparathyroidism, pseudohypoparathyroidism, vitamin D deficiency

Question 12

define hypoparathyroidism

Answer 12

decreased secretion or activity of parathyroid hormone (PTH)

Question 13

causes of hypoparathyroidism

Answer 13

idiopathic (low PTH), hypomagnesaemia (low [Mg2+]), suppression of PTH by raised plasma [Ca2+] (still low unbound [Ca2+])

Question 14

define pseudohypoparathyroidism

Answer 14

target organ is resistant to PTH due to defective Gs protein so no cAMP effect

Question 15

clinical features of pseudohypoparathyroidism

Answer 15

short stature, round face, low IQ, subcutaneous calcification and various bone abnormalities, associated endocrine disorders (e.g. hypothyroidism, hypogonadism)

Question 16

what does vitamin D deficiency cause in children

Answer 16

rickets

Question 17

what does vitamin D deficiency cause in adults

Answer 17

osteomalacia

Question 18

clinical features of vitamin D deficiency

Answer 18

decreased calcification of bone matrix resulting in softening of bone, causing bowing of bones in children and fractures in adults

Question 19

differential diagnosis for hypocalcaemia: all in common

Answer 19

all low plasma [Ca2+]

Question 20

differential diagnosis for hypocalcaemia: determining if vitamin D deficiency

Answer 20

low plasma [PO4 3-] (others are normal)

Question 21

differential diagnosis for hypocalcaemia: determining if hypoparathyroidism

Answer 21

low [PTH] (others are normal)

Question 22

define hypercalcaemia

Answer 22

high blood [Ca2+]

Question 23

endocrine causes of hypercalcaemia

Answer 23

primary hyperparathyroidism, tertiary hyperparathyroidism, vitamin D toxicosis

Question 24

clinical features of hypercalcaemia

Answer 24

polyuria and polydypsia

Question 25

what can hypercalcaemia cause

Answer 25

renal calculi