Calcium Dysregulation Flashcards
What hormone(s) increases calcium levels?
Vitamin D
Parathyroid hormone
What hormone(s) decreases calcium levels?
Calcitonin
How is vitamin D mentabolised?
UVB light 7 dehydrocholesterol Pre vitamin D3 Vitamin D3 OR Vitamin D2 from diet 25 hydroxylase in liver makes it 25(OH) cholecalciferol 1 alpha hydroxylase in kidney makes it 1,25 dihydroxy cholecalciferol= calcitriol
What is the active form of vitamin D called?
Calcitriol
What vitamin D enzyme is found in the liver?
25 hydroxylase
What vitamin D enzyme is found in the kidney?
1 alpha hydroxylase
What are the effects of calcitriol?
Effects bone, kidney and gut
Increases osteoblast activity (vit D for bone strength)
Works to increase calcium by increasing calcium absorption by bone
Increases Ca2+ reabsorption from kidney and gut
Increases phosphate reabsorption from kidney and from gut
What are the effects of PTH?
Increases calcium reabsorption from bone
Increases calcium reabsorbtion from gut and kidney
Increases phosphate absorbtion from gut
Increases phosphate excretion in the kidney
Increases 1 alpha hydroxylase activity in kidney
What does FGF23 do?
Blocks sodium phosphate co transporter in PCT, encouraging excretion of phosphate in the urine
It also inhibits calcitriol
This leads to less phosphate reabsorption from gut
What is calcitriol inhibited by?
FGF23
How does hypocalcaemia present?
Cats go numb: Convulsions Arrythmias Tetany Paraesthesia
What are the 2 signs of hypocalcaemia?
Chovstek’s sign- facial paraesthesia when you tap the zygomatic branch of the facial nerve
Trousseau’s sign- carpopedal spasm
What are the causes of hypocalcaemia?
Low PTH levels (surgical, autoimmune, magnesium deficiency, congenital)
Low vitamin D (diet deficiency, UV light etc)
How does hypercalcaemia present?
Stones- renal effects (nephrocalcinosis: kidney stones)
Abdominal moans- GI effects (anorexia, nausea, dyspepsia, constipation, pancreatitis)
Psychic groans- CNS effects (fatigue, depression, impaired concentration, altered mentation, coma)
What are the causes of hypercalcaemia?
Primary hyperparathyroidism- too much PTH
Malignancy- produce local factors to activate osteoclasts or make peptide that acts on PTH receptors
Vitamin D excess
What is the normal relationship between calcium and PTH? Describe why this relationship arises
As calcium falls, PTH rises
This is because PTH increases levels of calcium so is only released when calcium levels are low
Describe what happens in primary hyperparathyroidism and what the hormone levels are
Parathyroid gland adenoma resulting in excess PTH secretion,
hypercalcaemia and high PTH
Describe what happens in secondary hyperparathyroidism and what the hormone levels are
Vitamin D deficiency (due to lack in diet or no sunlight) leading to excess PTH to compensate, low calcium, high PTH, low vit D
Describe what happens in tertiary hyperparathyroidism and what the hormone levels are
Complication of renal failure, unable to make calcitriol so parathyroid glands become hyperplasic and make lots of PTH, high PTH, low vit D, high calcium
How is primary hyperparathyroidism treated?
Parathyroidectomy/tumor removal
How is secondary hyperparathyroidism treated?
Vitamin D supplements (25 hydroxy vitamin D)`
How is tertiary hyperparathyroidism treated?
Parathyroidectomy
What is calcium resorption? How does it affect calcium levels?
The process of removing old bone tissue via osteoclasts and laying down new bone tissue via osteoblasts, it increases calcium levels
What is the difference between calcitonin and calcitriol?
Calcitriol is the active form of vitamin D
Calcitonin is a hormone that reduces levels of calcium
What are the 2 ways we can take in vitamin D? What specific type of vitamin D is associated with each?
Sunlight- this involves vitamin D3
Diet- this involves vitamin D2
What are calcium, phosphate and PTH levels in primary hyperparathyroidism? Explain each one
Calcium is high due to excess PTH
Phosphate is low as PTH causes increased renal phosphate excretion
PTH is high as it isn’t suppressed by hypercalcaemia as there is a pituitary adenoma
What is the main difference between primary and secondary hyperparathyroidism?
In primary calcium is high but in secondary it is low because the high PTH is secondary to low calcium
When taking a diagnostic approach to hypercalcaemia, what do we always have to look at?
PTH
What is the normal PTH response to hypercalcaemia? When this doesn’t occur what can you suspect?
Normal response is for PTH to fall, this may not happen in malignancy or chronic renal failure
If a patient presents with hypercalcaemia and high PTH what are the possible diagnoses?
Primary hypercalcaemia due to pituitary adenoma
Tertiary hypercalcaemia due to chronic renal failure
What is the diagnostic approach to vitamin D deficiency?
Measure calcium, it will be low or low/normal
PTH should be high when measured
Measure vitamin D as 25 (OH) vitamin D
What form of vitamin D is hard to measure?
Calcitriol
