Flashcards in Calcium and Phosphate Metabolism Deck (54)
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1

What does bone turnover achieve?

➝ homeostasis of serum calcium and phosphate
➝ with PTH, vitamin D, calcitonin and FGF-23

2

What two things increase calcium?

➝ PTH
➝ Vitamin D

3

What decreases calcium?

➝ calcitonin

4

What lowers serum phosphate?

➝ FGF-23

5

How much calcium is in bone?

➝ 99%

6

How much calcium is intracellular?

➝ 1%

7

What is the concentration of extracellular calcium?

➝ 2.2-2.6mmol

8

What is the distribution of extracellular calcium?

➝ half is free
➝ half is albumin bound

9

At low concentrations what effect does PTH have?

➝ anabolic
➝ promotes formation of bone

10

What do prolonged high levels of PTH do?

➝ lead to an excess of bone resorption over formation and a rise in extracellular calcium

11

If PTH levels are persistently raised what do you have?

➝ pathological hypercalcaemia

12

What does PTH promote?

➝ resorption of calcium from the kidney tubule and increases in the excretion of phosphate

13

What % of phosphorous is in bone and in what form?

➝ 85%
➝ Hydroxyapatite

14

Where is the remainder of phosphate?

➝ intracellular

15

What is the concentration of extracellular H2PO4?

➝ 2.5-4.5mg/ dL

16

What are the clinical features of hypercalcaemia?

➝ Depression
➝ Fatigue
➝ anorexia
➝ vomiting
➝ nausea
➝ abdominal pain
➝ renal calcification
➝ bone pain

17

What are the severe clinical features of hypercalcaemia?

➝ cardiac arrythmias
➝ cardiac arrest
➝ death

18

What are the causes of hypercalcaemia in ambulatory patients?

➝ primary hyperparathyroidism

19

What is the cause of hypercalcaemia in hospitalised patients?

➝ malignancy

20

What are two less common causes of hypercalcemia?

➝ hyperthyroidism
➝ excessive intake of vitamin D

21

What are the serum biochemistry levels of
calcium, phosphate, alkaline phosphatase and creatinine in hypercalcemia?

➝ calcium : modest to marked increase
➝ phosphate : low or low normal
➝ alkaline phosphatase : raised in 20% of cases
➝ creatinine : elevated in long standing disease due to kidney damage

22

What is alkaline phosphatase?

➝ Enzyme found in the liver, bone and other tissues

23

Why is alkaline phosphatase increased in the presence of bone disease?

➝ it is a rough marker of bone turnover
➝ it can be elevated due to an increase in bone turnover

24

What is abnormal about these lab results and why?

Total calcium 2.85 mmol/L (2.20-2.52)
PTH 6.8pmol/L (1-6.9)

➝ the PTH levels are within the normal range but inappropriately normal
➝ the calcium levels are high
➝as calcium rises the PTH should decrease
➝ elevated calcium without suppressed PTH can still be a sign of hyperparathyroidism

25

What are the 3 categories of hypercalcemia of malignancy?

➝ Humoral
➝ metastatic
➝ Haematological

26

What is an example of humoral hypercalcemia of malignancy?

➝ lung carcinoma secreting PTHrp (PTH related peptide)
➝ actual PTH levels would be low
➝ parathyroid glands are responding appropriately to the raised calcium but they are not the source of it

27

How does metastatic hypercalcemia of malignancy arise?

➝ if the tumors metastasize to bone the tumor cells secrete cytokines which increase osteoclast formation over osteoblast and release calcium such as RANK-L

28

What is a haematological cause of hypercalcemia of malignancy?

➝ myeloma

29

What are the two most common causes of hypocalcaemia?

➝ vitamin D deficiency
➝ renal failure

30

What effect does renal failure have on vitamin D?

➝ impaired ability to produce vitamin D because the converting enzyme is in the kidney