11. Calcium abnormalities

Question 1

what is the effect of hypo- and hyper-calcaemia on nerve APs

Answer 1

Ca raises threshold for nerve membrane depolarisation and thus dev. on an AP

• hypocalcaemia: reduced membrane depolarisation threshold… increased excitability at neuromuscular junctions
• hypercalcaemia: increased membrane depolarisation threshold… reduced neuronal activity

Question 2

what is the main cause of hypocalcaemia

Answer 2

thyrectomy and inadvertant removal/ischaemia of parathyroid glands

Question 3

what are the symptoms of hypocalcaemia

Answer 3

CATs go Numb:

• convulsions
• arrhythmias
• tetany
• numbness/paraesthesia

Question 4

name 2 signs of hypocalcaemia

Answer 4

• carpopedal spasm

- Chvostek’s sign (twitching of mouth when tapping cheek)

Question 5

why can hypocalcaemia be fatal

Answer 5

laryngeal muscle paralysis

Question 6

what is the treatment for hypocalcaemia

Answer 6

IV calcium

Question 7

what are the consequences of decreased neuronal activity in hypercalcaemia

Answer 7

lethargy, depression, confusion and coma

Question 8

name 3 effects of hypercalcaemia at the kidneys

Answer 8

1. kidney stones
2. polyuria due to impaired Na+ and H2O reabsorption… dehydration
3. renal failure

Question 9

name the 3 main causes of calcium dysregulation

Answer 9

1. malignant hypercalcaemia
2. primary hyperparathyroidism
3. secondary hyperparathyroidism

Question 10

what are the 3 types of malignant hypercalcaemia

Answer 10

1. multiple myleoma (plasma cell neoplasm)
2. osteolytic bone metastases: breast, lung, renal, thyroid
3. squamous tumours of lung, head and neck - secrete PTH-related peptide which acts at PTH Rs

Question 11

what is the main difference between PTH and PTHrP

Answer 11

PTHrP does not cause a calcitriol increase as does not incresaed renal 1a-hydroxylase activity

Question 12

what is primary hyperparathyroidism

Answer 12

parathyroid adenoma causing excessive PTH secretion - increased serum Ca and decreased Pi

Question 13

which condition arises due to primary hyperparathyroidism

Answer 13

parathyroid bone disease, i.e. OSTEOPOROSIS

Question 14

what is secondary hyperparathyroidism

Answer 14

parathyroid hyperplasia (all 4 glands) as a result of vitD deficiency

Question 15

what are the effects of vitD deficiency on serum calcium and PTH

Answer 15

low calcitriol… decreased Ca absorption from GI tract… decreased serum Ca… increased PTH… increased osteoclast activity in order to mobilise Ca from bone

Question 16

what are the 2 main causes of vitD deficiency and which condition does each cause

Answer 16

• inadequate diet… RICKETS/OSTEOMALACIA

- chronic renal failure (causing failure of 1a-hydroxylation of vitD3)… renal osteodystrophy, i.e. OSTEOMALACIA

Question 17

what is alkaline phosphatase and in which condition would it be increased

Answer 17

enzyme released during bone activity

increased levels in all 3 causes but esp. in malignant hypercalcaemia

Question 18

why does prostate cancer metastasis not cause hypercalcaemia

Answer 18

causes osteoblastic metastases rather than osteoclastic metastases