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s3 - MSK, Derm, Cardio, Neuro, Pharm > Ca2+ / Phosphate Balance > Flashcards

Ca2+ / Phosphate Balance Flashcards

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Dermatology Board Prep flashcards
1
Q

Where is phosphate reabsorbed?

By which transporter?

A

Proximal tubule

85% is reabsorbed via the NaPi2a/NaPi2c cotransporters here

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2
Q

5 Functions of Ca2+

A
  • bone growth/remodelling
  • secretion e.g. of NTs
  • muscle contraction
  • blood clotting
  • 2ndry messenger
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3
Q

4 steps of bone remodelling

A
  • stem cell differentiation to osteoclasts
  • reabsorption of bone
  • MO/Mononuclear cell mopping up debris
  • Laying down new osteoid by osteoblasts
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4
Q

3 hormones favouring osteoclast activation

3 hormones favouring osteoblast activation

A

osteoclast + : thyroxine, vit A, PTH

osteoblast + : oestrogens, androgens, PTH

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5
Q

Where in parathyoid glands is PTH made?

A

Chief cells

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6
Q

If calcium is low, the parathyroids detect this and respond by…

A

releasing more PTH

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7
Q

4 actions of PTH…

A
  • stimulates osteoblasts to produce M-CSF and RANK ligand to increase bone reabsorption
  • increases Ca2+ reabsorption in the DCT
  • increases phosphate excretion
  • stimulates conversion of cholecalciferol into active 1,25-dehydroxy vitamin D3 “calcitriol” in the kidney via increasing the enzyme 1 a hydroxylase
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8
Q

3 actions of Vitamin D in Calcium homeostasis…

A
  • increases Ca2+ absorption in the GUT
  • synergies with PTH on bone
  • stimulates CaBP synthesis (ca binding protein)
  • inhibits PTH synthesis and 1-a hydroxylase
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9
Q

Causes of Hypercalcemia

A
  • Hyperparathyroidism
  • Cancer
  • Hypervitaminosis (D)
  • Increased bone turnover
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10
Q

Cause of Primary Hyperparathyroidism

A
  • Chief cells no longer recognise calcium is high
  • due to single adenoma causing inability to switch off PTH
  • or diffuse hyperplasia
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11
Q

Secondary vs. Tertiary Hyperparathyroidism

A

2ndry is a compensatory hyperfunctioning of parathyroid glands due to hypocalemia, peripheral PTH resistance, renal insufficiency, vit D deficiency..

whereas 3ary is following 2ndry when despite the underlying abnormality having been corrected corrected, the glandular hyperfunctioning continues

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12
Q

Hormonal causes of Hypercalcemia due to malignancy: 3 examples

A
  • metastatic solid tumours
  • osteoclast activating factor (lymphoma, myeloma)
  • PTH-RP from lung tumours, lymphoma, myeloma
  • PTH from small cell lung carcinoma
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13
Q

How may inflammatory markers e.g. from granulomatous diseases, lead to raised calcium?

A

Macrophages express 1-a hydroxylase which activates vitamin D3 consequently Ca2+ levels rise

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14
Q

How can immobilisation cause hypercalcemia?

A

Bone is laid down along lines of stress via release of piezoelectricity (from pressure+latent heat) which osteoblasts are sensitive to. Without this you get an imbalance of bone remodelling

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15
Q

Which asymptomatic condition is a loss of function mutation in CaSR (calcium sensing receptor) gene.

A

FHH-Familial Hypocalciuric Hypercalcemia

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16
Q

List 5 classic hypercalcemia symptoms.

A
  • Neurologic: decreased conc, confusion, fatigue
  • Renal: polyuria, nephrocalcinosis, DI
  • MSK: weakness, bone pain, osteoporosis
  • CVS: short QT interval, HT, bradycardia
  • GIT: anorexia, nausea, constipation, peptic ulcer
17
Q

Hypercalcemia sign in the eye

A

Keratinosis-milky calcium deposit ring around pupil

18
Q

Hypercalcemia, 3 scan investigations

A
  • SestaMBI Scan (localise adenoma both - thyroid = para)
  • Neck Ultrasound, Renal Tract Ultrasound
  • DEXA (bone density)
19
Q

5 Hypercalcemia treatments

A
  • saline rehydration (dilute so kidneys can clear Ca)
  • furosemide (Ca excretion)
  • pamidronate infusion (binds to hydroxyapetite crystals so osteoclasts cant)
  • calcitonin
  • prednisolone (steroid to decrease infammatory causes)
  • dialysis
20
Q

Where is calcitonin made and what is its action?

A

C cells of thyroid gland

oppose action of PTH (decrease Ca)

21
Q

What is the calcimimetic cinacelet used to treat?

A

Hypercalcemia e.g. for 2dry hyperPTH as it binds to the parathyroid calcium sensing receptor and decreases calcium release

22
Q

3 Causes of HYPOcalcemia with Low PTH

A
  • hypoparathyroidism
  • pseudohypoparathyroidism
  • activating mutation of the Ca Sensing R
23
Q

3 Causes of HYPOcalcemia with High PTH

A
  • vitamin D deficiency (renal/liver disease or resistance)
  • poor dietary calcium
  • malabsorbtion
24
Q

1 and 2dry HYPOparathyroidism

A

1ary can be congenital/autoimmune

2nry can be post neck surgery/trauma or from radioiodine

25
Q

3 factors contributing to low vit D due to poor sunlight exposure

A
  • suncream
  • obesity
  • lattitde
  • skin pigmentation
26
Q

What is calcium chelation/precipitation?

A

Citrate in blood (e.g.transfusions) is a cheletic agent so it binds to Ca2+ and takes it out of circulation having an anti-coagulant effect and lowering plasma calcium levels.

(calcium is vital in the clotting cascade, ^this decreases chance of clot formation)

27
Q

5 common symptoms of HYPOcalcemia

2 Acute manifestations

2 Chronic Manifestations

A

Common: muscle cramps, paraesthesia, SOB due to bronchospasm, confusion, seizures, Chvostek’s (facial nerve tap->contraction) and Trosseau’s sign

Acute: Syncope, congestive HF

Chronic: Dry skin, coarse hair, itching

28
Q

3 signs/symptoms of vit D3 deficiency

A
  • aches/pains in bones
  • proximal myopathy
  • low phosphate
  • children: knocked knees/bow legs

s3 - MSK, Derm, Cardio, Neuro, Pharm (9 decks)

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