Chapter 3 Calcium, Phosphorus, Magnesium, and Kidney Stones Flashcards Preview

Nephrology and Hypertension Board Review > Chapter 3 Calcium, Phosphorus, Magnesium, and Kidney Stones > Flashcards

Flashcards in Chapter 3 Calcium, Phosphorus, Magnesium, and Kidney Stones Deck (66)
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1

What percentage of total body calcium is stored in bones and teeth?

99% of total body calcium is stored in bones and teeth.

2

Outside of bones and teeth, where else is calcium stored in the body?

1% of total body calcium is found in the intracellular fluid compartment.

0.1% of total body calcium is found in the extracellular fluid compartment.

3

How is calcium in plasma stored?

Calcium in plasma comes as:
- Ionised calcium (40 - 50%)
- Protein bound, mainly to albumin (40 - 50%)
- Complexed (to phosphate, citrate and bicarbonate) (10%).

4

What changes the distribution of plasma calcium?

pH and levels of albumin change the distribution of plasma calcium.

5

How does acidaemia change the distribution of plasma calcium?

Acidaemia increases the percentage of ionized calcium at the expense of calcium bound to proteins.

* Increased hydrogen ions in acidaemia bind to plasma proteins, displacing calcium from plasma proteins and increasing the relative concentration of ionised calcium.

6

How does alkalaemia change the distribution of plasma calcium?

Alkalemia decreases the percentage of ionized calcium.

* Decreased hydrogen ions in alkalaemia results in some dissociating from plasma proteins, in exchange for calcium, thereby decreasing the plasma concentration of ionized calcium.


]. Hypoalbuminemia increases the ionized [Ca ++ ], whereas hyperalbuminemia decreases ionized plasma [Ca ++

7

Are individuals with alkalaemia or acidaemia more susceptible to tetany with hypocalcaemia?

Alkalaemia

Individuals with alkalemia are susceptible to tetany (tonic muscular spasms), whereas individuals with acidemia are less susceptible to tetany with hypocalcaemia.

8

How does the proportion of ionised calcium change with differing levels of albumin?

Ionised calcium increases with hypoalbuminaemia.

Ionised calcium decreases with hyperalbuminaemia.

9

In brief, what are the four physiological functions of calcium?

1. Skeletal composition
2. Neuromuscular excitation
3. Skeletal muscle contraction
4. Cardiac muscle contraction

10

What is normal dietary calcium intake per day?

Normal dietary calcium intake is 1g per day.

11

What percentage of dietary calcium is absorbed by the gastrointestinal tract?

20% of dietary calcium is absorbed by the gastrointestinal tract.

12

What does calcitriol do?

Calcitriol (1,25 vitamin D) binds to its VDR receptor and:
- Increases TRPV6 expression
- Increases calbindin D9K
- Increases Calcium ATPase

These all increase calcium absorption from the gut.

13

In brief, what is TRPV6?

TRPV6 (transient receptor potential) is a calcium channel that facilitates apical uptake of calcium by enterocytes.

14

What increases intestinal calcium absorption?

Increased intestinal calcium absorption occurs in:
- Acromegaly
- Excess vitamin D ingestion

15

What decreases intestinal calcium absorption?

Decreased intestinal calcium absorption occurs in:
- High vegetable fibre diet
- Low calcium/phosphate ratio diets
- High fat diet
- Older patients
- Oestrogen deficiency
- Corticosteroid use
- Diabetes
- Kidney disease
- Gastrectomy
- Bowel malabsorption

16

What percentage of calcium is ultra filterable?

55% of calcium is ultrafilterable (diffusible) - ionised calcium and complexed calcium.

17

What factors influence the load of ultrafilterable calcium?

The factors that influence the ultrafilterable calcium load are:
- Glomerular filtration rate
- Glomerular surface
- Ultrafiltration coefficient Kf
- Ultrafilterable calcium load.

18

What does PTH do to the ultrafiltration coefficient Kf?

PTH reduced the ultrafiltration coefficient Kf.

19

What hormones increase distal calcium reabsorption?

PTH and calcitriol increase distal calcium reabsorption.

20

What drugs increase calcium reabsorption in the distal tubules?

Amiloride and thiazides increase calcium reabsorption in the distal tubules.

21

What is the daily urinary excretion of calcium?

The daily urinary excretion of calcium is <0.3g/d, which is minimal given the amount that is filtered and this is due to its effective reabsorption along the entire nephron.

22

What is the most biologically active form of vitamin D?

1,25 vitamin D is the most biologically active form of vitamin D.

23

What does 1,25 vitamin D do?

1,25 vitamin D:
- Increases GI absorption of calcium and phosphate
- Stimulates FGF-23 and 24-hydroxylase
- Provides negative feedback on PTH.

24

What is the primary function of PTH?

The primary function of PTH is to increase ionised calcium levels in response to hypocalcaemia.

25

In brief, what are the function of PTH?

PTH:
- Induces phosphaturia
- Increases 1,25 vitamin D.

26

How is FGF-23 produced?

FGF-23 is a peptide produced by osteocytes and osteoblasts.

27

In brief, what are the main actions of FGF-23?

1. Phosphaturia
2. Inhibition of PTH
3. Reduces 1,25 vitamin D activity

28

How does FGF-23 cause phosphaturia?

FGF-23 suppresses two genes that encode sodium-phosphate transporters in the proximal tubules.

FGF-23 suppresses NPT2a and NPT2b.

29

What causes upregulation of FGF-23?

FGF-23 is upregulated by phosphate, although not necessarily hyperphosphataemia, and 1,25 vitamin D.

30

In brief, what are the causes of hypercalcaemia?

1. Excess calcium ingestion
2. Excessive vitamin D ingestion
3. Bone metastatic disease
4. Osteoclastic activating factors from malignancy
5. Immobilisation
6. Primary hyperparathyroidism
7. Granulomatous disease
8. Medications
9. Familial hypocalciuric hypercalcaemia
10. Jansen disease
11. Paget disease
12. Loss of function of vitamin D-24-hydroxylase