Pharmacology and testing disorders of calcium metabolism

Question 1

Calcium homeostasis is controlled by which 3 factors?

Answer 1

1. Parathyroid hormone
2. Vitamin 3
3. Calcitonin

Question 2

Where in the body does calcium absorption/excretion take place?

Answer 2

• intestinal absorption
• renal excretion
• release and uptake from bone

Question 3

What is the effect of parathyroid hormone on urinary excretion of ions?

Answer 3

Decreases urinary excretion of calcium and increases urinary excretion of phosphate

Question 4

What are the clinical signs of milk fever?

Answer 4

• skeletal muscle weakness, tremors, ataxia, recumbency
• head tucked into flank
• hypothermia
• bloat
• constipation
• urine retention
• dystocia
• dilate pupils

Question 5

When can hypocalcaemia occur in sheep and dogs?

Answer 5

Sheep = late gestation in sheep with multiple foetuses
Dog = Peak lactation in small breeds with large litters

Question 6

What is the cause of chronic renal disease?

Answer 6

• less phosphate excreted in urine which leads to hyperphosphatemia
• decrease in normal kidney function
• renal secondary hyperparathyroidism causes bone demineralisation and rubber jaw

Question 7

What effect does hyperphosphatemia have on the body?

Answer 7

• Directly stimulates the release of PTH (parathyroid hormone)
• Forms a complex with ionised calcium causing hypocalcaemia and release of PTH
• Retained phosphate also decreases production of calcitriol (active form of vitamin D)

Question 8

What are the 3 different disorders of the parathyroid that can occur?

Answer 8

• Primary hyperparathyroidism
• Primary hypothyroidism
• Secondary hyperparathyroidism

Question 9

What can be measured on a blood test to look for a disturbance of calcium metabolism?

Answer 9

1. Total serum calcium = ionised calcium + protein bound calcium
   Normally a 50:50 ratio
   Only ionised calcium is physiologically active
2. PTH

Question 10

Which 2 factors can affect protein bound calcium?

Answer 10

Blood albumin concentration

Acid-base status

Question 11

What would be an indicator on a blood test for hyperparathyroidism?

Answer 11

• Increased PTH

- Increased blood calcium

Question 12

How would you differentiate the blood test result to determine between secondary hyperparathyroidism or PTH independent hypercalcaemia?

Answer 12

2ndary hyperparathyroidism = low/normal blood calcium levels with high blood PTH

Hypercalcaemia = High blood calcium and low plasma PTH

Question 13

Name 4 calcium salts

Answer 13

Calcium gluconate
Calcium carbonate
Calcium chloride
Calcium borogluconate

Question 14

What are vitamin D preparations used to treat?

Answer 14

• Iatrogenic hypoparathyroidism

- Renal secondary hyperparathyroidism

Question 15

Where is orally administered calcium absorbed from?

Answer 15

The small intestine

Question 16

What is the absorption of calcium facilitated by?

Answer 16

Vitamin D3
PTH
Acidic pH

Question 17

What is the absorption of calcium interfered by?

Answer 17

Dietary fibre
Phytates
Steatorrhea (fat in faeces)
Uraemia (raised level of blood urea)

Question 18

What are 2 adverse effects of calcium administration?

Answer 18

• Hypercalcaemia

- Rapid IV affects on the heart

Question 19

The increase of P increases the release of PTH by which 3 mechanisms?

Answer 19

• Direct effect on parathyroid gland to promote release
• Indirect effect by decreasing calcitriol production
• Formation of complex with ionised Ca which decreases the amount ionised

Question 20

What is the name of vitamin D, and what is its role?

Answer 20

Calcitriol

Regulates calcium absorption from the gut

Question 21

Phosphate absorption is regulated by…?

Answer 21

Calcitriol

Question 22

Which 2 substances mobilise calcium ions and phosphate from the bone matrix?

Answer 22

PTH

Calcitriol

Question 23

How does PTH affect regulation of phosphate?

Answer 23

PTH inhibits reabsorption so increases excretion

Question 24

How does PTH work to increase calcium reabsorption from the gut?

Answer 24

Mobilises calcium ions from bone, enhances reabsorption in the kidney, stimulates synthesis of calcitriol
It also promotes phosphate excretion which increases the conc of calcium ions in the blood plasma

Question 25

Where is Calcitonin secreted from?

Answer 25

By C cells of thyroid follicles, driven by hypercalcaemia

Question 26

What are the actions of calcitonin?

Answer 26

Decrease bone reabsorption, and decrease calcium ion and phosphate reabsorption in the kidney

Question 27

When would calcium salts be using in maintaining calcium homeostasis?

Answer 27

• Dietary deficiency
• Post partum hypocalcaemia
• To treat hyperphosphatemia

Question 28

What are 2 adverse effects when using calcium salts?

Answer 28

• Oral calcium salts can cause GI upset

- Intravenous administration can cause cardiac arrhythmias and arrest

Question 29

When would vitamin D preparations be used to balance calcium homeostasis?

Answer 29

Chronic management of hypocalcaemia which most commonly occurs following a thyroidectomy or immune mediated hypoparathyroidism

Question 30

Define ‘Narrow therapeutic index’

Answer 30

Those drugs where small differences in dose or blood concentration may lead to dose and blood concentration dependent, serious therapeutic failures or adverse drug reactions.

Question 31

What are the adverse effects of vitamin D preparations?

Answer 31

• Narrow therapeutic index
• Hypercalcaemia
• Hyperphosphatemia
• Nephrocalcinosis (excess calcium is deposited in the kidneys)