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Endocrine > Calcium homeostasis > Flashcards

Calcium homeostasis Flashcards

1
Q

where is the majority of calcium stored?

A
  • 99% is stored in the skeleton (1.0kg)
  • 1mmol/l is in the ECF
  • 0.1mmol/l intracellular
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2
Q

what are the three major factors of calcium control?

A

•Parathyroid hormone (PTH)

•

dihydroxyvitamin D

  • and
  • Calcitonin (minor role in control)
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3
Q

At what time of day is the circadian rhythm highest?

A

Circadian rhythm highest at night, lowest in the morning.

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4
Q

when calcium level is high, what happens to the parathyroid hormone?

A

parathyroid hormone is inhibited with high caclium

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5
Q

What effect does phosphate, Aluminium, and magnesium have on parathyroid hormone?

A

Magnesium = has a similar effect as calacium, however low magnesium disallows calcium to raise - so you must correct Mg levels if you’re going to correct calcium levels

Aluminium - inhibits PTH

Phosphate- increases secretion of PTH

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6
Q

Does PTH have a direct effect on the GI system?

A

no - indirectly it effects it through vitamin D

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7
Q

What is the effect of PTH on bones, kidneys and gut?

A

Bones

  • increase bone resorption
  • stimulate the osteoclast
  • increase calcium and phosphate release from bone

Kidney

  • enhance renal calcium re-absorption
  • increase renal phosphate excretion
  • promote conversion of 25 OH-vitamin D to the active metabolite 1,25 dihydroxyvitamin D

GI

  • increase calcium absorption indirectly
  • enhance the action of 1,25 dihydroxyvitamin D in the gut
  • increase calcium + phosphate absorption
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8
Q

What are some reasons for Vit. D deficiency?

A

lack of sunlight

poor diet

liver disfunciton

malabsorption

kidney disease

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9
Q

What is the effect of Calcitonin?

A

•Reduces blood calcium levels

•

  • Suppresses the osteoclast
  • Inhibits urinary reabsorption of calcium and phosphate
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10
Q

What cells release Calcitonin?

A

•Released by parafollicular C cells of the thyroid gland

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11
Q

Hypercalcaemia has what sort of symptoms?

A

In order of descending frequency

–Fatigue

–Polydipsia- due to nephrogenic diabetes insipidus (low vasopressin)

–Confusion

–Anorexia

–Depression

–Polyuria

–Nausea

–Proximal myopathy

–Constipation

–Nephrolithiasis

–Pancreatitis

–Peptic ulcer disease

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12
Q

What is the most likely reason for hypercalcaemia?

A

Overactive thyroid gland (hyperparathyroidism) – 50%

  • Malignancy (of thyroid, blood, bone, breast (not prostate)) – 45%
  • Others

–Granulomatous disease

–Drugs - thiazides, lithium, vitamin A (bone resorption) and D (high phosphate + high calcium)

–Renal failure

–Pagets disease, thyrotoxicosis, immobilisation

–FHH

–Addisons disease, milk alkali, hypophosphatasia

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13
Q

Why does Addison’s disease cause high calcium?

A

not sure why may be due to enhanced renal tubular calcium reabsoprtion due to volume depletion and increased calcium mobilisation from the bone into the serum

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14
Q

Why does prostate cancer cause HYPOcalcaemia?

A

prostate cancer releases osteoBLASTS instead of osteoclasts - lead to bone building and more calcium absorption by bones

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15
Q

what can hyperparathyroidism often be confused with?

A

FHH - familial … something… hypercalcaemia

  • to differentiate between the two, check if calcium level is high AND PTH is high - then check if the patient has a high or low calcium urine excretion rate - if it is low, then it is FHH. If it is high then it is hyperparathyroidism

*your first step to find cause of hypercalcaemia should be testing the PTH level *

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16
Q

How can lung cancer cause hypercalcaemia?

A

lung cancer may have metasticized into bone…

Small cell tumours can release a peptide which has similar properties as the PTH

tumour can release cytokines which stimulate osteoclasts - lead to excessive bone turnover and hypercalcaemia

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17
Q

hyperparthyroidism is more commmon in men or women?

A

women

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18
Q

in 85% of hyperparathyroisim, how many of the glands are enlarged?

A

majority of cases, only one of the parathyroid glands are enlarged

19
Q

if you have high calcium hyperparathyroidism- what is your phsophate level likely to be?

A

low phosphate b/c of excessive phsophate excresion in the kidneys

20
Q

if your alkaline phsophatase is high… you have a problem with what?

A

either liver or bone

  • to decide which one, look at other liver function markers like Gamma GT (if also high then likely the liver)
21
Q

Why might you have a high level of calcium in the urine even if there is increased calcium reabsorption from the kidneys?

A

just b/c there is an overall huge amount of calcium in the body

22
Q

what is cinacalcet?

A

used in patients with hypercalcaemia - it is a calcimimetic that binds to the calcium sensing receptor on the Para thyroid gland and suppressis the hormone release

23
Q

What is Familial Hypocalciuric Hypercalcaemia?

A

this presents similarly to hyperparathyroidism - where you get a high calcium and a high PTH - but these people get a low urine calcium excression rate

24
Q

what are the cuases of low parathyroid hormone levels?

A

parathyroid agenesis

parathyroid destruction (surgery-often actually in the first 24 hours, radiation, infiltration by metastases or systemic disease)

  • autoimmune

reduced parathyroid funciton

25
Q

hypocalcaemia is related to what level of Vitmain D?

A

low levels of vitamin D

26
Q

if there is a low calcium and low PTH level- what is the likely diagnosis?

A

damage to the parathyroid gland - most likely from recent surgery

27
Q

severe hypocalcaemia can potentially cause what?

A

MI due to prolonged QT interval

28
Q

Waht are the two signs of hypocalcaemia?

A

Trousseaus sign

and

Chvostek’s sign

29
Q

What is the likely diagnosis in low calcium and high phosphate and PTH is undetectable?

A

hypoparathyroidism

30
Q

what is the likely diagnosis if low serum calcium, low phosphate, high alkaline phsophate and elevated PTH ?

A

Osteomalacia

31
Q

What is the main consideration when treating hypocalcaemia?

A

protect the heart - give calcium gluconate immediately, and correct low magnesium

32
Q

In endocrinology .. too much of something does what to the hormone that produces it?

A

too much of a hormone inhibits the gland that produces it

too little increases the activity of the gland that produces it

  • if it doesn’t, there is somethign wrong-
33
Q

peak bone mass is at what age?

A

25 years of age

34
Q

in females, when does bone mass start to drop off?

A

after menopause - estrogen is bone protector (same with men with testosterone)

35
Q

describe bone remodelling

A

osteoclasts - eat away chunk of bone - and then your osteoblasts come in and make a new bone structural unit

*in a healthy individual, osteoclast/osteoblast activity should be equivalent

36
Q

Where does the DXA scan look at?

A

Hip, wrist and back

37
Q

What is a T score/Z score?

A

T score refers to the number of standard deviations below or above the average peak bone mass in young premenopausal adults of the same sex (if more than -2.5 standard deviations below that, then it’s classified as osteoporosis)

Z score indicates the number of standard deviations below or above the average bone mass in an age and gender matched population. (use Z score to diagnose osteoporosis in PREMENOPAUSAL women)

38
Q

treatments for osteoporosis act on what?

A

they either stimulate bone production (rhPTH-parathyroid hormone stimulates bone formation, but we don’t use more than 2 yr b/c studies show it increases risk for osteosarcomas)

or

inhibit bone destruction (bisophsphates - inhibit osteoclasts from binding to the bone -

39
Q

What is the 1st line of treatment for osteoporosis?

A

Bisphosphonates - old people take it in the morning b4 mass due to risk of reflux

40
Q

Teriparatide.. what is this?

A

treatment for osteoporosis- recombinant human parathyroid hormone - runs risk of hypercalcuria - do not use with bisphosphates

41
Q

What is RANK ligand ?

A

RANK ligand binds to RANK - to stimulate the precursor osteolast to become a mature osteoclast -

*osteoprotagan inhibits the RANK ligand from binding*- Denosumab works by imitating this osteoprotagan

42
Q

Paget disease is a disease of what?

A

disease of the osteoclasts - they increase bone reabsorption and then when the osteoblasts remake the bone, they are poor quality and increase risk of fracture - so bones get big but htey’re weak

*this disease is associated with hearing loss and blindness due to increase in ear bones pressing on cochlea, associated with osteosarcomas due to increased bone turnover - also associated with heart failure due to requirement of blood to reach the new bone - so you’ll actually hear a trill in the bone

43
Q

how do you treat paget’s disease?

A

With bisphosphonates - worksvery well nearly cure them

Endocrine (16 decks)

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