L16 - Disorders of calcium metabolism

Question 1

summarise the bone remodelling cycle

Answer 1

1. resorption
2. reversal
3. formation
4. quiescence

Question 2

resorption initiated by….

Answer 2

osteoclasts

———————-> secretion of HCl

Question 3

what occurs during reversal…

Answer 3

• osteoblasts come and lay new bone : osteoid
• osteoblasts on top of osteoid
• move up to bone surface

Question 4

osteoid

Answer 4

unmineralised bone

Question 5

what occurs during formation in the bone making cycle?

Answer 5

• osteoid gets mineralised
• osteoblasts get trapped in matrix
• longer process

Question 6

primary role of 1,25, hydroxy vitamin D

Answer 6

• activate calcium transport in intestine, increase intestinal calcium absorption
• inhibits kidney from calcium excretion

Question 7

features of hypercalcaemia

Answer 7

• lethargy and general aches
• polyuria, polydipsia
• anorexia, nausea, vomitting
• dehydration
• constipation
• psychosis
• bradycardia and heart block
• kidney failure

Question 8

PTH-dependent hypercalcaemia

Answer 8

PTH normal or raised

Question 9

PTH-independent hypercalcaemia

Answer 9

low PTH

• thyrotoxicosis

Question 10

what might be witnessed in primary hyperparathyroidism as a result of excessive bone resorption?

Answer 10

• osteoporosis / fractures
• subperiosteal resorption
• osteitis fibrosa cystica
• brown tumour

Question 11

osteitis fibrosa cystica

Answer 11

• cystic expansions of bone

Question 12

brown tumour

Answer 12

• due to increased haemosiderin deposition
• The brown tumor is a bone lesion that arises in settings of excess osteoclast activity
• such as hyperparathyroidism.

Question 13

subperiosteal resorption

Answer 13

• increased action of osteoclasts

Question 14

definition of secondary hyperparathyroidism

Answer 14

• elevated PTH
• but normal calcium
• Secondary hyperparathyroidism is a condition in which a disease outside of the parathyroid glands causes all of the parathyroid glands to become enlarged and hyperactive.
• most common causes : are kidney failure and vitamin D deficiency.

Question 15

describe tertiary hyperparathyroidism?

Answer 15

• chronic hypocalcaemia
• parathyroid responds with elevated PTH
• but if it goes unchecked the gland enlarge and become autonomous
• secrete PTH in the absence of hypocalcaemia

Question 16

trousseau’s sign

Answer 16

• inflate BP cuff to 10mmHG about systolic BP
• leave cuff on to induce local hypoxia
• observe flexion at wrist, occurs slowly
• present in 94% of hypocalcaemia cases

Question 17

chvostek’s sign

Answer 17

• tap over the area of facial nerve
• observe twitching of facial muscles, twitching of lip to spasm of all facial muscles
• absent in 1/3rd of hypocalcaemia cases

Question 18

How may sepsis lead to hypocalcaemia in patients?

Answer 18

1. increased cytokine production
   a) reduced parathyroid gland activity
   b) reduced renal 1-a-hydroxylation
   c) resistance to 1,25(OH)2D
2. LEADS TO LOW IONISED Ca2+

Question 19

psuedohypocalcaemia

Answer 19

• contamination of blood sample with EDTA