2. Calcium And Phosphate

Question 1

What is diffusible calcium?

Answer 1

Free ionised Ca2+ (cellular processes)

Complexed calcium - bound to negatively charged molecules like oxalate

Question 2

What is not diffusible calcium?

Answer 2

Ca2+ bound to negatively charged proteins e.g. albumin

Question 3

Where is calcium reabsorbed?

Answer 3

65% in PCT
25% in Thick ascending limb
8% in DCT
1.5% in CD
Excrete 0.5%

Question 4

How does reabsorption of PO4 3- occur?

Answer 4

With Na+ ions at apical membrane of tubular cells

Question 5

What is the relationship between concentrations of Ca2+ and PO4 3- in the body?

Answer 5

Concentrations are inversely proportional

Question 6

What happens in hypocalcemia?

Answer 6

Decreased Ca2+ results in neuromuscular excitability leading to tetany with convulsions, hand and feet muscle cramps and cardiac arrhythmias

Question 7

What are the causes of hypocalcemia?

Answer 7

CKD due to hyperphosphatasemia and low levels of activated vit D
Hypoparathyroidism
Rickets and osteomalacia
Tissue injury
Alkalosis

Question 8

How can alkalosis cause hypocalcemia?

Answer 8

Reduces amount of H+ available to bind to protein, so more Ca2+ can bind to protein
Results in decreased ionised Ca2+, although total Ca2+ remains the same

Question 9

What is the treatment for hypocalcemia?

Answer 9

Oral or IV calcium and patients with CKD will benefit form alfacalcidol (vit D analogue)

Question 10

What happens in hypercalcaemia?

Answer 10

Makes cells less excitable resulting in slow reflexes, muscle weakness and constipation

Question 11

What are the signs and symptoms of hypercalcaemia?

Answer 11

Polyuria
Polydipsia
Bones (bone pain and fractures)
Stones (real calculi)
Groans (abdominal pain, vomiting, constipation)
Moans (depression or confusion)

Question 12

What is the treatment for hypocalcemia?

Answer 12

Treat underlying cause with fluids for rehydration and bisphosphonates

Question 13

What are the causes of hypercalcaemia?

Answer 13

Primary hyperparathyroidism
Sudden acidosis
Increase intestinal absorption due to excess vit D or ingestion of calcium
Bone destruction 
Granulomatous disease
Drugs
Tertiary hyperparathyroidism in CKD
Hypermagnesemia

Question 14

What is hypohosphatemia?

Answer 14

Excessive loss of PO4 3-

Question 15

What are the causes of hypophosphatemia?

Answer 15

Hyperparathyroidism
Reduced absorption from GI
Significantly reduced intake - malnourished, anorexia nervosa
Refeeding syndrome
Diabetic ketoacidosis
Respiratory alkalosis

Question 16

What are the signs of hypophosphatemia?

Answer 16

Stones (kidney and gallbladder)
Thrones (polyuria)
Bones (pain)
Groans (constipation and muscle weakness)
Psychiatric overtones (depressed mood and confusion)

Question 17

What is the treatment for hypophosphatemia?

Answer 17

Oral or IV phosphate and close monitoring of blood vessels

Question 18

What are the causes of hyperphosphatemia?

Answer 18

CKD
Secondary hyperparathyroidism
Pseudohypoparathyroidism (kidneys don’t respond to PTH)
Hypoparathyroidism
Excessive intake
Cell death
Respiratory acidosis
Diabetic ketoacidosis

Question 19

What are the symptoms of hyperphosphatemia?

Answer 19

No symptoms with mild

Severe: spontaneous firing of neurons, tetany, involuntary contraction of muscles, kidney stones

Question 20

What is the treatment for hyperphosphatemia?

Answer 20

Phosphate binders and forced diuresis