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MEH > Calcium Metabolism > Flashcards

Calcium Metabolism Flashcards

1
Q

How much Ca is in the body?
How much is in the bone?
What about the rest?

A

1kg approx.

99% in bone, as Hydroxyapatite crystals

The rest is extracellular (Serum)

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2
Q

What is the total Serum Ca concentration?

In what 3 forms does Ca travel in the plasma?
Which form is physiologically active?

A

2.2-2.7 mmol/L

  • Free ions, Physiologically active (45%)
  • Bound to plasma proteins (45%)
  • Complexed with organic anions, such as citrate (10%)
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3
Q

What is the normal range of free Ca ions in plasma?

Describe the regulation of plasma phosphate levels

A

1.0 to 1.3 mmol/L

Not strictly regulated, so levels fluctuate especially after a meal

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4
Q

In what 2 ways are Ca and PO4 homeostasis linked to each other

A
  • Primary comments of hydroxyapatite crystals

- Regulated by same hormones

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5
Q

Which 3 hormones are involved in Ca and phosphate homeostasis

Which 3 organ systems do they act on?

Compare the hormones’ actions on Ca and Phosphate

A
  • Parathyroid Hormone (PTH)
  • Calcitriol (Activated Vitamin D)
  • Calcitonin (Lesser extent)
  • Bone
  • Kidneys
  • GI tract (Indirectly)

Actions on Ca and phosphate are typically opposed

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6
Q

State the net Ca uptake of the Intestines per day

State the net Ca uptake of Bone per day

State the net Ca excretion of Kidney per day

A

Intestines: 175mg (Absorb 500, secrete 325)

Bone: 0 (280mg deposition, 280mg resorption)

Kidney: (Filter 10kg) <2% of filtered loads

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7
Q

In a pension who is in Ca balance, how does urinary excretion of Ca compare to net absorption of Ca?

A

They are the same

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8
Q
  1. Where is PTH made?
  2. What is 1,25(OH)2D or 1,25(OH)2D3 also called?
  3. Where is Calcitonin made?
A
  1. Chief cells of parathyroid gland
  2. Calcitriol
  3. Parafollicular/ C Cells of Thyroid Gland
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9
Q

PTH is a straight chain polypeptide hormone.

How do Low and High serum Calcium affect its synthesis and degradation?

A

Low serum Ca;

  • Up regulates gene transcription
  • Prolongs mRNA survival

High serum Ca;

  • Down regulates gene transcription
  • Accelerates degradation
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10
Q

What cells make and degrade PTH?

What PTH’s half life?

When is PTH synthesised?

A

Chief cells do both

Half life of 4 mins

Continuously synthesised

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11
Q

What are the effects of PTH on the Kidney, Intestines and Bone?

A

Kidney: Increased Ca reabsorption and Phopshate excretion

Bone: Increased resorption (More Ca enters blood)

Intestines: Activated Vit D-> Increased Ca absorption

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12
Q

How are laboratory Ca tests corrected and why?

A

Levels are corrected depending on amount of Albumin, as the tests measure TOTAL Calcium, not just the free ions

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13
Q

Outline how Sunlight is used to make Calcitriol

A
  1. Sunlight converts cholesterol to Vit D3 (Cholecalciferol)
  2. In liver, Vit D3 hydroxylated-> 25(OH)D
  3. In kidney, 25(OH)D hydroxylated-> 1,25(OH)2D (Calcitriol)
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14
Q

Compare the functions and time scales of PTH and Calcitriol (Activated Vit D)

A

PTH;

  • Increases serum Ca
  • Short term serum Ca regulation

Calcitriol;

  • Increases serum Ca
  • Long term serum Ca regulation

(Act via different mechanisms)

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15
Q

What are the 2 major forms of Vitamin D?

A 
Vit D3 (Cholecalciferol) (Animal sourced foods)
Vit D2 (Ergocalciferol)(Plant sourced foods)
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16
Q

What are the effects of Calcitriol on the Kidney, Intestines and Bone?

A

Kidney: Increased reabsoprtion of Ca

Intestines: Increased Ca absorption

Bone: Increased resorption

17
Q

What is PTHrP? What can it lead to?

What tumours can make it?

A

Parathyroid Hormone related Peptide is a peptide produced by tumours

Can cause hypercalcaemia

Squamous tumours of Lung, Head and Neck

18
Q

What 3 types of cancer commonly prove PTHrP

A

Breast
Prostate
Occasionally Myeloma

19
Q

What are 3 common effects of PTH and PTHrP

What is difference?

A
  • Increased Resorption of bone
  • Reduced Ca excretion in kidney
  • Reduced Phosphate reabsorption in kidney

Unlike PTH, PTHrP doesn’t increase Calcitriol (by increasing renal C-1 hydroxylase activity)

20
Q

What does Calcitonin do?

How important is this hormone?

Suggest 1 possible use

A

Lowers serum Ca levels

Not very important, no apparent effect on Ca homeostasis

Preservation of maternal skeleton during pregnancy

21
Q

Name 4 common cancers that metastasise to bone and cause hypercalcaemia

A

Breast
Lung
Kidney
Thyroid

22
Q

What are 6 common sites for bone metastasis

A
  • Skull
  • Ribs
  • Vertebrae
  • Pelvis
  • Proximal femur
  • Proximal humerus
23
Q

Explain the symptoms of Hypocalcaemia (Give 4 symptoms)

A

Calcium raises the threshold for nerve membrane depolarisation

Hyper excitability in nervous system;

  • Parasthesia
  • Tetany (muscle spasms)
  • Paralysis
  • Convulsions
24
Q

What are 6 symptoms of chronic hypercalcaemia

A
  • Kidney stones (renal caniculi)
  • Constipation
  • Dehydration
  • Kidney damage
  • Tiredness
  • Depression
25
Q

What are 5 symptoms of severe hypercalcaemia?

A
  • Lethargy
  • Weakness
  • Confusion
  • Coma
  • Renal failure (+Polyuria)
26
Q

At what serum Ca level, do you get SEVERE hypercalcaemia

How is it treated?

A

> 3 mmol/L

Rehydration

27
Q

Why is EDTA/ Citrate used during blood donations?

A
  • EDTA/ Citrate is used to chelate calcium ion
  • Ca ions have a role in blood clotting
  • Prevents donated blood from clotting
28
Q

Why are massive blood transfusion recipients given IV calcium?

A

Citrate in donated blood binds with Ca, decreasing free Ca ions in serum

IV Ca gluconate restores free Ca ion levels

29
Q

Compare Osteoporosis and Osteomalacia in terms of;

  1. Mineral:Matrix
  2. Physiological process
  3. Consequences
  4. Causes/ risk factors
A

Osteoporosis:

  1. Normal mineral:matrix, decreased bone density
  2. Degeneration of already constructed bone
  3. Brittle bones, prone to fracture
  4. Post menopause/ Smoking/ Low BMI/ Immobility

Osteomalacia:

  1. Decreased mineral:matrix
  2. Abnormality of bone building in children/ mineralisation in adults
  3. Soft bones, prone to bending
  4. Vit D deficiency

MEH (20 decks)

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