Clinical Chemistry 3 - Divalent Ions Flashcards
What is the overall effect of PTH?
To increase calcium and decrease phosphate concentrations
The secretion of PTH from the parathyroid glands is triggered by what?
Low serum calcium
What effect does PTH have on bone?
Increases osteoclast activity to cause calcium and phosphate release from bone
What happens to phosphate once it has been taken out of bone?
It is excreted by the kidneys
What effect does PTH have on the kidneys?
Increased calcium reabsorption and decreased phosphate reabsorption
In addition to altering reabsorption of calcium and phosphate, what other action does PTH have at the level of the kidneys?
Increases production of calcitriol
Where is vitamin D hydroxylated?
First in the liver, then in the kidneys
1, 25-dihydroxy-vitamin D3 is the active form of vitamin D. What is this known as?
Calcitriol
Calcitriol production is stimulated by what?
PTH release
What is the major action of calcitriol?
Increased calcium and phosphate absorption from the gut
In addition to the gut, calcitriol also causes calcium and phosphate to be absorbed from where?
Kidneys
What effect does calcitriol have on bone?
Increased bone turnover
What effect does calcitriol have on PTH?
Inhibition of its release
Disordered regulation of calcitriol underlies which clinical condition?
Familial normocalcaemic hypercalciuria
Familial normocalcaemic hypercalciuria is a major cause of the formation of which type of renal stone?
Calcium oxalate
Where is calcitonin produced?
C-cells (parafollicular cells) of the thyroid
When does calcitonin have an effect on calcium metabolism?
When there is hypercalcaemia
How does calcitonin decrease serum calcium levels in response to hypercalcaemia?
Reduces osteoclastic activity
Calcitonin levels can be used as a tumour marker for what?
Medullary thyroid cancer
A low level of which electrolyte prevents PTH release, and therefore may cause hypocalcaemia?
Magnesium
‘Stones, bones, groans and psychic moans’ classically describes the symptoms of which electrolyte imbalance?
Hypercalcaemia
What will an ECG of hypercalcaemia show?
Shortened QT interval
What are the two most common causes of hypercalcaemia?
Primary hyperparathyroidism and hypercalcaemia of malignancy
What are some reasons that malignancies may cause hypercalcaemia?
Bony metastases, myeloma, PTH-related-peptide release
What happens to phosphate and ALP levels in hypercalcaemia of malignancy?
Increased
If a patient has a calcium level > 3.5mmol/l and is symptomatic, how should they be treated?
Saline and bisphosphonates
What are some mild features of hypocalcaemia?
Cramps and peri-oral numbness
What are some severe features of hypocalcaemia?
Carpo-pedal spasm, laryngospasm, seizures
Trousseau’s and Chvostek’s signs indicate what electrolyte abnormality?
Hypocalcaemia
What does Trousseau’s sign show?
On inflating a BP cuff, the wrist and fingers draw together
What does Chvostek’s sign show?
The corner of the mouth twitches when the facial nerve is tapped over the parotid gland
What does an ECG of hypocalcaemia show?
Prolonged QT interval
What happens to phosphate levels in patients with hypocalcaemia due to CKD, hypoparathyroidism, hypomagesaemia or vitamin D deficiency?
High
What are some causes of hypocalcaemia with a low or normal phosphate level?
Osteomalacia, respiratory alkalosis, over-hydration, pancreatitis
How should mild symptoms of hypocalcaemia be treated?
Oral calcium supplements
In hypocalcaemia due to CKD, supplementation of what else as well as calcium may be necessary?
Vitamin D
How should severe symptoms of hypocalcaemia be treated?
10mls 10% calcium gluconate IV over 30 minutes (and repeated as necessary)
Hyperphosphataemia is most commonly caused by what?
CKD
How is hypophosphataemia treated?
Oral or IV phosphate supplementation
IV phosphate supplementation should never be given to which patients?
Those who are hypercalcaemic or oliguric
Plasma concentrations of magnesium tend to follow those of which other ions?
Calcium and potassium
What is the main cause of hypermagnesaemia?
CKD
If hypermagnesaemia is severe, what kind of symptoms does it cause?
Symptoms due to CNS and respiratory depression
Other than hypokalaemia, what other electrolyte abnormality also enhances digoxin toxicity?
Hypomagnesaemia
How does a zinc deficiency usually occur?
Parenteral nutrition or very poor diet
What are some symptoms of zinc deficiency?
Alopecia, dermatitis, night blindness and diarrhoea
