Calcium Homeostasis

Question 1

Hypocalcemia symptoms

Answer 1

• paraesthesia (numbness/tingling)
• muscle spasm
• tetany
• seizures/fits
• arrythmias
• Chvostek’s sign (twitch of facial muscles when tapping cheek)
• Trousseau’s sign (inflate blood pressure cuff on arm and leave for 3 minutes, +ve = carpopedal spasm)

Question 2

Hypercalcemia symptoms

Answer 2

• nausea
• peptic ulcers
• constipation
• soft tissue calcification
• mental disturbances
• renal stones
• polyuria
• renal failure

Question 3

How is calcium stored in bone?

Answer 3

• stored as hydroxyapatite

- calcium bound to PO4 (Ca released when bone broken down)

Question 4

Calcium in blood

Answer 4

• can measure total blood Ca
• only ionised Ca physiologically important

Total Ca conc = 2.2-2.6 mmol/L
Ca2+ conc = 1.1-1.3 mmol/L

Question 5

What is adjusted calcium?

Answer 5

measured total calcium can be adjusted for albumin
(Calcium sticks strongly to proteins in blood, especially albumin. If albumin low, calcium levels could be measured as low even if ionised calcium in blood normal)
decreased albumin may mask hypercalcemia
formula is used (does not need to be memorised)

Question 6

Response to decreased circulating calcium

Answer 6

• calcium sensing receptor responds
• increased parathyroid hormone (PTH) synthesis + release from parathyroid gland chief cells

PTH acts in 3 ways:

• promotes Ca reabsorption via kidney
• stimulates osteoclast resorption of bone (releases Ca from bone)
• calcium absorption in small intestine increases via vitamin D synthesis
• calcitonin decreases, removing inhibitory effect on osteoclasts allowing PTH stimulation to result

Question 7

Response to increased circulating calcium

Answer 7

• calcium binds to transmembrane receptor
• acts as antagonist, decreasing PTH release
• thyroid gland releases calcitonin
• osteoclast activity inhibited
• Ca2+ reabsorption in kidneys decreases
• Ca2+ level in blood decreases

Question 8

Blood Calcium levels for hypocalcemia and hypercalcemia

Answer 8

Hypercalcemia: ACa (adjusted calcium) >2.6 mmol/L
Hypocalcemia: ACa < 2.2 mmol/L

Question 9

Most common hypercalcemia causes

Answer 9

• hyperparathyroidism

- hypercalcemia of malignancy

Question 10

Most common hypocalcemia causes

Answer 10

• renal failure
• hypoparathyroidism
• vitamin D deficiency/malabsorption

Question 11

Calcium daily intake requirements for females, males, growing skeleton, in osteoporosis, maximum

Answer 11

Females = 350mg minimum
Males = 450mg minimum
Growing skeleton = 750mg
Osteoporosis = 1500mg
Maximum = 3000mg