Calcium Metabolism Flashcards Preview

Z OLD ESA 1- Metabolism > Calcium Metabolism > Flashcards

Flashcards in Calcium Metabolism Deck (75):
1

What regulate calcium balance?

Gut, Kidneys, Bone

2

What is the importance of calcium?

In plays a critical role in many cellular processes

3

Give 6 roles of calcium

- Hormone secretion 
- Muscle contraction 
- Nerve conduction 
- Exocytosis 
- Activation of many enzymes
- Intracellular second messenger

4

How does Ca 2+ serve as an intracellular second messenger?

By carrying information from the cell membrane to the interior of the cel

5

What is it important that the body regulates very tightly?

The plasma concentration of free ionised calcium ([Ca 2+ ])

6

Why is free ionised calcium concentration controlled?

Because this is the physiologically active form of the metal

7

At what level is free plasma [Ca 2+ ] maintained?

Within the narrow range of 1.0-1.3mmol/L

8

Where does phosphate play a critical role?

In cellular energy metabolism

9

Why does phosphate play a critical role in cellular energy metabolism?

Because it’s part of the adenosine triphosphate molecule

10

Other than in ATP, where else does phosphate play a crucial role?

In activation and deactivation of enzymes

11

How does regulation of plasma phosphate differ from calcium?

It is less tightly regulated, and the levels fluctuate throughout the day, particularly after means

12

Why are calcium homeostasis and phosphate homeostasis intimately linked?

- Because calcium and phosphate are the principal components of hydroxyapatite crystals 
- They are regulated by the same hormones

13

What is the formula for hydroxyapatite crystals?

Ca 10 (PO 4 ) 6 (OH) 2

14

What do hydroxyapatite crystals constitute?

The major portion of the mineral phase of bone

15

What hormones regulate calcium and phosphate?

Primarily parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D (calcitrol), and, to a lesser extent, calcitonin

16

Where do PTH, calcitriol and calcitonin act?

The organ systems of bone, kidney and GI tract

17

What is the purpose of PTH, calcitriol and calcitonin?

To control the levels of calcium and phosphate ions in the plasma

18

Why are the actions PTH, calcitriol and calcitonin on calcium and phosphate typically said to be opposed?

A particular hormone may elevate the level of one ion while lowering the other

19

Where is calcium location?

Within bone

20

How much calcium is in the bone?

~1kg

21

What is the total amount of calcium in the extracellular pool?

Only a fraction of the amount in bone, about 1g

22

What is the typical daily dietary intake of calcium?

~800 to 1200mg

23

What are the major dietary sources of calcium?

Dairy products

24

What do the intestines do regarding calcium?

- Absorb ~half of the dietary calcium (~500mg/day) 
- Secrete calcium for removal from body (~325mg/day)

25

What is the net intestinal uptake of calcium?

About 175mg/day

26

What happens to bone in a steady state?

Calcium deposition in bone of about 280mg/day is matched by an equal amount of calcium reabsorption

27

How much calcium to the kidneys filter a day?

10 times the total extracellular pool of calcium, about 10,000mg/day

28

What happens to 98% of the pool that is filtered by the kidneys?

It’s reabsorbed

29

What is the net renal excretion of Ca 2+ ?

Less than 2% of the filtered load

30

What happens regarding kidney filtering in a person in calcium balance?

Urinary excretion (~175mg/day) is the same as net absorption by the GI tract

31

How does calcium exist in plasma?

- As free ionised species 
- Associated with anionic sites on serum proteins, especially albumin 
- Complexed with a low-molecular-weight organic anion

32

Give 2 examples of low-molecular-weight organic anions calcium may be complexed with?

#NAME?

33

What is the total concentration of all three physiochemical forms of calcium in the plasma?

Normally 2.2-2.7mmol/L

34

How much calcium is free in healthy individuals?

~45%

35

How much calcium is bound to proteins in healthy individuals?

~45%

36

How much calcium is bound to small organic anions in healthy individuals?

10%

37

What form of calcium is most important with regard to regulating the secretion of PTH?

Ionised form

38

What is the ionised form of calcium involved in?

Most of the biological actions of calcium

39

What do common laboratory tests measuring calcium usually measure?

Total calcium, including not only physiologically active free ionised calcium, but calcium bound to albumin and other proteins

40

How is it determined if free calcium is in the correct range or not?

The levels are corrected depending on the level of albumin

41

What is hypocalcaemia?

When calcium levels are too low

42

What is the consequence of hypocalcaemia?

Hyper-excitablity of the nervous system, including the neuromuscular junction, leading to parasthesia

43

What does paraesthesia lead to?

Tetany, paralysis and convulsions

44

What is hypercalcaemia?

Calcium too high

45

What are the consequences of hypercalcaemia?

Formation of kidney stones, constipation, dehydration, kidney damage, tiredness and depression

46

What is it clear from the consequences of dysregulation of serum calcium?

That it’s very important that levels are maintained within set limits

47

What are the two key hormones in calcium regulation?

- PTH 
- Calcitriol

48

What do PTH and calcitriol both act to do?

Raise serum calcium concentrations

49

How do PTH and calcitriol differ?

They act by different mechanisms, and over different time scales

50

What is the short term regulation of serum calcium under control of?

PTH

51

What is long term regulation of serum calcium under control of?

Calcitriol

52

What is vitamin D?

A collective term for a group of prohormones

53

What are the 2 major forms of vitamin D?

- D2 (ergocalciferol) 
- D3 (cholecalciferol)

54

Where is vitamin D obtained from?

#NAME?

55

Is vitamin D reactive?

No, it’s biologically inert

56

What must happen for vitamin D to be activated in the body?

Two hydroxylation reactions

57

What is calcitriol?

An active form of vitamin D found in the body, involved in calcium regulation

58

Other than the prohormones, what else is the term vitamin D used to refer to?

The metabolites of vitamin D, and other analogues of these substances

59

What is parathyroid hormone related peptide (PTHrP)?

A peptide

60

What produces PTHrP produced by?

Tumours

61

What may production of PTHrP lead to?

Hypercalcaemia

62

Where can the measurement of PTHrP be useful?

In determining the cause of an otherwise unexplained hypercalcaemia

63

What does the secretion of PTHrP from cancer cells lead to?

Humeral hypercalcaemia of malignancy (HHM)

64

Where is PTHrP commonly produced?

In patients with breast or prostate cancer, and occasionally in patients wiht myeloma

65

What does PTHrP share with PTH

Many actions

66

What does the similarities in action of PTH and PTHrP lead to?

- Increased calcium release from bone 
- Reduced renal calcium excretion 
- Reduced renal phosphate reabsorption

67

What activity does PTHrP not increase?

C-1 hydroxylase

68

What is the result of PTHrP not increasing renal C-1 hydroxylase activity?

It doesn’t increase calcitrol concentration, unlike PTH

69

What does calcitonin do?

In an animal, lowers serum calcium levels

70

What does calcitonin do in humans?

Little function

71

What suggests that calcitonin has little function in humans?

It appears to lack pathology associated with either hypo or hyper secretion

72

Where is calcitonin secreted from?

Thyroid gland

73

What happens if the thyroid gland is removed or destroyed, regarding calcitonin?

The lack of secretion appears to have no effect on calcium homeostasis

74

Where might calcitonin be important?

In pregnancy

75

Why may calcitonin be important in pregnancy?

May serve to preserve maternal skeleton