Calcium physiology

Question 1

What are the functions of calcium

Answer 1

Bone and tooth structure​

Mineral store​

Action potentials (cardiac muscle)

Membrane excitability​

2nd messenger
-Muscle: excitation-contraction coupling
-Gland secretion
-Non-steroid hormone action​

Co-factor in metabolic pathways

Blood clotting

Question 2

What procedure is made possible due to ability of bone remodelling

Answer 2

Orthodontics

Question 3

What are the normal calcium conc
-diffusible and non-diffusible

Answer 3

Diffusible calcium​
-Ionised calcium 1.2 mmol/l​
-Bound to citrate 0.2 mmol/l​

Non-diffusible calcium​
-Bound to Protein 1.2 mmol/l​

Total 2.6 mmol/l

Question 4

What is the total calcium conc

Answer 4

2.6 mmol/l

Question 5

Where does calcium pass through in the body

Answer 5

G.I. tract
Plasma + interstitial fluid
Kidney
Exchangeable bone

Question 6

Where is calcium maintained

Answer 6

Stable bone

Question 7

How is calcium lost

Answer 7

Faeces
Urine

Question 8

How can we gain calcium

Answer 8

Diet

Question 9

How is calcium homeostasis maintained

Answer 9

Parathyroid hormone
Calcitonin
Vitamin D

Question 10

How does the parathyroid hormone act to increase plasma calcium

Answer 10

Increased resorption of bone (osteoclasts)​

Increased Ca2+ resorption in kidney (with  PO4 resorption)​

Increased uptake of Ca2+ from the intestines (assisted by Vitamin D)

Question 11

What stimulates the parathyroid hormone to maintain calcium homeostasis

Answer 11

Decreased plasma Calcium conc

Question 12

How does the parathyroid hormone act to increase calcium levels in plasma

Answer 12

Kidney
-Increases formation of 1,25 OH vit D, leads to increased absorption of calcium in intestines
-Increases Ca2+ resorption while increasing phosphate excretion

Bone
-Resorption and release of calcium and phosphate

Question 13

What role does calcitonin play in maintaining calcium homeostasis

Answer 13

Increases formation of bone
Decreases calcium resorption in kidney

SEEMS TO PLAY VERY MINOR ROLE - lack has no effect

Question 14

What stimulates the production of calcitonin in calcium homeostasis

Answer 14

Secreted fromthyroid glands in response to high calcium levels in plasma

Question 15

What does Vit D do in calcium homeostasis

Answer 15

Used to produce 1, 25 (OH)2 Cholecalciferol
(calcitriol)

Question 16

How is calcitriol produced

Answer 16

Vitamin D3 cholecalciferol
reacts with 25-hydroxylase in liver
producing 25 (OH) cholecalciferol
which reacts with 1 alpha hydroxylase in kidney regulated by PTH
producing 1, 25 (OH)2 Cholecalciferol or calcitriol

Question 17

How is Vitamin D3 produced

Answer 17

Dietary Vit D combines with 7-dehydrocholesterol synthesised in skin

Question 18

How does calcitriol act in calcium homeostasis

Answer 18

INTESTINE:
-Calcium absorption

KIDNEY:
-Calcium retention
-Phosphate retention

BONE:
-Calcium release
-Phosphate release

OVERALL - increased levels of calcium and phosphate in plasma

Question 19

What hormones decrease bone mass while increasing bone resorption

Answer 19

-Cortisol
-Parathyroid hormone
-Thyroid hormone

Question 20

What hormones increase both bone formation and bone mass

Answer 20

-Calcitonin
-Growth hormone
-IGF-1 (insulin growth factor)
-Insulin
-Oestrogen
-Testosterone

Question 21

What are osteocytes

Answer 21

Trapped osteoblasts in the bone matrix

Question 22

What do osteoblasts produce

Answer 22

Collagen fibres forming a matrix later mineralised by calcium salts (osteoid)

Question 23

How do osteocytes contact other cells

Answer 23

Via long cytoplasmic processes

Question 24

Where in the bone do osteocytes lie

Answer 24

Within the bony lacunae

Question 25

Where would osteoclasts be found

Answer 25

Lie in depressions (Howship’s lacunae)

Question 26

What is hypercalcaemia

Answer 26

Raised calcium levels

Question 27

What is hypocalcaemia

Answer 27

Reduced calcium levels

Question 28

How does hypocalcaemia occur

Answer 28

Decreased calcium intake
Excessive calcium loss
Alkalosis (low calcium)

Question 29

What can low calcium levels cause

Answer 29

Increased nerve excitability:

‘pins and needles’; muscle spasms,
Trousseau’s sign; Chvostek’s sign

Question 30

What can cause alkalosis

Answer 30

Hyperventilation such as a panic attack

Question 31

What disorders can occur through an over/uncersecretion of the calcium regulating hormones

Answer 31

Hyperparathyroidism (parathyroid hormones)
-Osteitis fibrosa cystica
-Defective mineralisation of teeth due to undersecretion of hormone (low calcium)

Vitamin D deficiency
-Rickets (Kids)
-Osteomalacia (adults)

Calcitonin
-Non obvious consequences in over or undersecretion

Question 32

What is Osteitis fibrosa cystica

Answer 32

Areas of demineralisation in the skull and leg bones caused by hyperparathyroidism

Question 33

Why does a Vit D deficiency cause rickets

Answer 33

Decreased calcium uptake from the G.I. tract which leads to undermineralised bone which lacks rigidity

Question 34

What are 2 types of bone diseases

Answer 34

Osteoporosis:​
-Decreased bone mass and density​

Osteopetrosis​

-Increased bone mass and density

Question 35

What is osteoporosis and it’s symptoms

Answer 35

Reduced bone density​

Loss of matrix with 2o loss of mineral​

Fractures common​

Common in elderly​

Affects men and women; but is evident earlier in women (menopause)

Question 36

What causes osteoporosis

Answer 36

Lack of plasma Calcium levels
Corticosteroids
Nutritional deficiency

Question 37

What is osteopetrosisand it’s symptoms

Answer 37

Increased bone density​

Reduced blood supply​

Prone to fracture and chronic infection​

Difficult extractions​

Tooth roots indistinct on radiographs​

Mandible > maxilla