S9 Calcium Metabolism

Question 1

What 13 things does calcium regulate?

Answer 1

• builds and maintains bones and teeth
• regulates heart rhythm
• eases insomnia
• passage of nutrients in and out of the cell walls
• blood clotting
• nerve and muscle function
• lowers BP
• normal kidney function
• activity of some enzymes and hormones receptor binding
• reduced blood cholesterol levels
• reduced incidence of colon cancer
• intracellular signally pathways
• nerve transmission

Question 2

How is calcium important in blood clotting? What does this mean you need to consider when taking blood samples/giving blood transfusions?

Answer 2

It’s factor IV in the clotting cascade?

Use a calcium chelator to prevent clotting

Question 3

Where is most calcium in the body?

Answer 3

In bones where it is hydroxyapatite crystals

Question 4

What 3 hormones are involved in regulation of calcium and phosphate?

Answer 4

• parathyroid hormone
• calcitriol
• calcitonin

Question 5

What cells in the parathyroid gland secrete PTH?

Answer 5

Chief cells

Question 6

What regulates PTH synthesis?

Answer 6

Serum calcium levels

Question 7

What organs does PTH act on?

Answer 7

• bone
• intestine/gut (via calcitriol)
• kidneys

Question 8

What physiological effects does PTH have on bones, the intestine/gut and the kidney?

Answer 8

Bone - increases resorption of calcium from bone (activates osteoclasts) - calcium and phosphate released into blood

Intestine/gut - activates vitamin D/calcitriol by activating renal C-1 hydroxylase - increases calcium uptake from GI tract

Kidney - decreases loss of calcium in urine, increased reabsorption of calcium ions

Question 9

What is the action of PTH on the bone?

Answer 9

1. PTH induces osteoblastic activity - to release cytokines on cell surface
2. These cytokines stimulate differentiation and activity of osteoclasts and protect osteoclasts from apoptosis
3. PTH decreases osteoblast activity, meaning osteoclasts can work
4. This leads to reabsorption of mineralised bone and release of inorganic phosphate and calcium ions into the extracellular fluid

Question 10

What are the different forms of vitamin D?

Answer 10

1. Vitamin D3 (cholecalciferol) hormone precursor - provided by UVB light on skin or from diet
2. 25(OH)D pre-hormone substrate - produced in lover from vitamin D3
3. 1,25(OH)2D - produced in the kidney from 25(OH)D

Question 11

What is the negative feedback loop if there’s a decrease in plasma calcium?

Answer 11

1. PTH secretion increases
2. Calcitriol levels increase in kidney which acts on the gut, absorbing more calcium from diet
3. Calcium reabsorption in the kidney (distal tubule and collecting duct)
4. Increased bone breakdown, decreased bone building

The opposite happens for an increase in plasma calcium

Question 12

What are the symptoms of chronic hypercalcaemia?

Answer 12

Stones
Moans (depression)
Groans (abdominal pain)
Bones (muscle aches)

Question 13

What is more dangerous hypocalcaemia or hypercalcaemia?

Answer 13

Hypocalcaemia

Question 14

What does hypocalcaemia lead to?

Answer 14

Hyperexcitability of the neuromuscular junction

A lower serum calcium concentration causes increase in Na+ entry into neurones which leads to depolarisation and increased chance of an action potential

Question 15

What are the signs and symptoms of hypocalcaemia?

Answer 15

• pins and needles
• tetany (muscle spasms)
• paralysis
• convulsions

Question 16

What are the symptoms of severe hypercalcaemia? When is hypercalcaemia severe?

Answer 16

• lethargy
• weakness
• confusion
• coma
• renal failure
  All due to polyuria and dehydration

Serum calcium levels over 3.0mmol/L

Question 17

What is the main treatment for serve hypercalcaemia?

Answer 17

Rehydration

Question 18

What are the main causes of hypercalcaemia?

Answer 18

• malignant osteolytic bone metastasis
• multiple myeloma
• cancers that metastasise to bone - breast, lung, thyroid, renal

Question 19

What are common sites for bone metastasis?

Answer 19

• vertebrae
• pelvis
• proximal part of femur
• proximal part of humerus
• ribs
• skull

Question 20

How does parathyroidism affect serum levels of calcium and phosphate?

Answer 20

Causes serum calcium to rise and serum phosphate to fall

Question 21

How does primary hyperparathryoidism occur?

Answer 21

One of the 4 parathyroid glands develops an adenoma and secretes excessive PTH

Question 22

How does secondary hyperparathryoidism occur?

Answer 22

All 4 parathyroid glands become hyperplastic - seen in patients with vitamin D deficiency

Question 23

What could vitamin D deficiency be due to?

Answer 23

Dietary/environmental

Or

Due to chronic renal failure (vitamin D not hydroxylated)

Question 24

What are the symptoms of primary hyperparathyroidism?

Answer 24

Stones - kidney stones, polyuria
Moans - tired, exhausted, depressed
Groans - constipation, peptic ulcers, pancreatitis
Bones - bone and muscle aches

Question 25

Hypercalcaemia suppresses neuronal activity so what are the symptoms?

Answer 25

• lethargy
• confusion
• coma

Question 26

Hypocalcaemia leads to excitable nerves so what are the symptoms?

Answer 26

• tingling
• muscle tetany
• epilepsy

Question 27

When do symptoms of hypocalcaemia develop (at what concentration)?

Answer 27

Below 2.10mmol/L

Question 28

When is symptomatic hypocalcaemia most commonly seen?

Answer 28

Seen in post total-thyroidectomy patients

Question 29

What are the sensory symptoms of hypocalcaemia?

What are the motor symptoms of hypocalcaemia?

Answer 29

• tingling around the mouth and in the fingers
• tetany of muscles
• carpopedal spasms

Question 30

What is the difference between osteomalacia and osteoporosis?

Answer 30

Osteomalacia - a normal structure, under mineralised

Osteoporosis - degraded structure, fully mineralised

Question 31

What is osteomalacia due to?

Answer 31

A vitamin D deficiency - means less calcitriol available to absorb calcium from the gut

Less calcium means less mineralisation of bone