L7 Plasma Calcium

Question 1

What physiological processes does calcium play a role in?

Answer 1

• Muscle contraction
• Blood coagulation
• Enzyme activation
• Neurotransmitter and hormone release
• Structural component of teeth and bones

Question 2

What is the normal plasma calcium concentration range?

Answer 2

2.2 - 2.6mM

Question 3

What are the 3 forms calcium can be present in?

Answer 3

• Protein bound calcium: cannot diffuse through membranes, not usable by tissues
• Ionised/free calcium: physiologically active
• Complexed/chelated calcium: calcium bound to phosphate, bicarbonate, sulphate, citrate or lactate

Question 4

What are the conesequences of ionised calcium levels being too high or low?

Answer 4

Too high = kidney stones

Too low = neuronal hyper-excitability, constant muscle contraction

Question 5

What are the 3 methods of calcium regulation?

Answer 5

• Absoprtion via intestines
• Excretion via kidneys/urine
• Temporary storage via bones

Question 6

What are the calcium reuqirements for people of different ages?

Answer 6

18 = 1300mg/day
19-50 = 1000mg/day
Over 51 = 1200mg/day
Pregancy/breastfeeding = 1300mg/day

Question 7

Describe acute calcium control.

Answer 7

• Maintenance of constant free calcium concentration in plasma
• Mostly through rapid exchange between bone and ECF

Question 8

Describe chronic calcium control.

Answer 8

• Maintenance of total level of calcium in the body long term
• Adjusts absorption of calcium from the GI tract and amount excreted through urine

Question 9

Plasma calcium concentration is controlled by which hormones?

Answer 9

In order of importance:

• Parathyroid hormone
• Calcitriol (1,25-dihydroxycholecalciferol)
• Calcitonin

Question 10

Which cell type has an essential role in the exchange of calcium between ECF and bone?

Answer 10

Osteocytes

Question 11

What does the parathyroid gland monitor?

Answer 11

The concentration of calcium in the blood that perfuses the gland.

Question 12

What is the major cell type of the paraythroid gland and its funciton?

Answer 12

Chief cells:

• Calcium sensing action
• Produce and secrete parathyroid hormone in response to hypocalcaemia

Question 13

Describe parathyroid hormone.

Answer 13

• Peptide hormone
• Short half life (5 mins) so rapidly inactivated
• Continuously secreted at very low rate
• Exerts effects on bone, kidneys and gut (indirectly)
• Secretion stimulated by hypocalcaemia, inhibited by hypercalcaemia

Question 14

Explain the principles effects of parathyroid hormone.

Answer 14

• Increases expression of enzyme 1α-hydroxylase, which activates vitamin D
• Prevents excretion of calcium from urine
• Increases osteoclast activity, causing bone resorption to increase calcium

Question 15

What are the 2 forms of vitamin D?

Answer 15

• Vitamin D2: ergocalciferol found in food supplements

- Vitamin D3: cholecalciferol found in diet and synthesised in skin in presence of sunlight

Question 16

Vitamin D is relatively inactive so is converted to what?

Answer 16

1,25-dihydroxycholecalciferol (calcitriol)

Question 17

How is vitamin D converted to calcitriol?

Answer 17

• 7-dehydrocholesterol is converted to cholecalciferol in the skin (vitamin D3)
• Cholecalciferol is converted to 25-hydroxyvitamin D3 in the liver
• Converted to 1,25-hydroxyvitamin D in the kidney through the action of the enzyme 1α-hydroxylase (parathyroid hormone increases expression of this enzyme)
• Converted to active form of vitamin D (calcitriol)

Question 18

Explain the actions of calcitriol (1,25-dihydroxycholecalciferol)

Answer 18

• Acts on cell of the GI tract to increase production of calcium transport proteins
• Causes increased calcium uptake from the GI tract
• Also receptors for calcitriol in the bone, which causes increased rate of bone resorption
• Minor effect on the kidneys in decreasing urinary loss of calcium

Question 19

What type of hormone is calcitriol?

Answer 19

Steroid hormone

Question 20

Where is calcitonin secreted from?

Answer 20

From the parafollicular cells of the thyroid gland.

Question 21

What is the role of calcitonin?

Answer 21

Decreases plasma calcium.

• Little importance in adults but more important in children
• Inhibits osteoclast activity
• Increases excretion of calcium and phosphate by the kidneys

Question 22

What other hormones have minor roles in plasma calcium regulation?

Answer 22

• Oestrogen and androgens
• Growth hormone
• Adrenal glucocorticoids

Question 23

Describe hypercalcaemia.

Answer 23

• Caused by primary hyperparathyrodisim
• Autonomous secretion of parathyroid hormone
• 85% of cases caused by a parathyroid adenoma (benign tumour)
• Presents as kidney stones, digestive issues, brain fog, depression, muscle weakness

Question 24

Describe hypocalcaemia.

Answer 24

Commonly due to vitamin D deficiency

• Caused by poor diet, malabsoprtion, decreased sunlight, liver or kidney disease
• Causes increased excitability of nervous tissue, pins and needles, muscle cramps and convulsions
• Can lead to osteomalacia (adults) or rickets (children)

Question 25

What is osteomalacia?

Answer 25

Osteomalacia = normal bone mass but reduction in bone mineral density

Question 26

What is the presentation of vitamin D deficiency?

Answer 26

• Increased PTH

- Decreased or normal plasma calcium due to compensatory rise in PTH

Question 27

What is the presentation of chronic renal disease?

Answer 27

• Increased PTH

- Decreased or normal plasma calcium

Question 28

What are the effects of hyperparathyroidism in dentistry?

Answer 28

• Calcium loss of maxilla and mandible
• Increased trabecular bone
• Decreased cortical bone
• Increased incidence of tori