Calcium physiology Flashcards by Niamh Sands

What are the functions of calcium

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

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What procedure is made possible due to ability of bone remodelling

Orthodontics

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

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

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What is the total calcium conc

2.6 mmol/l

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Where does calcium pass through in the body

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

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Where is calcium maintained

Stable bone

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How is calcium lost

Faeces
Urine

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How can we gain calcium

Diet

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How is calcium homeostasis maintained

Parathyroid hormone
Calcitonin
Vitamin D

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How does the parathyroid hormone act to increase plasma calcium

Increased resorption of bone (osteoclasts)

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

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

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What stimulates the parathyroid hormone to maintain calcium homeostasis

Decreased plasma Calcium conc

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

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

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What role does calcitonin play in maintaining calcium homeostasis

Increases formation of bone
Decreases calcium resorption in kidney

SEEMS TO PLAY VERY MINOR ROLE - lack has no effect

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What stimulates the production of calcitonin in calcium homeostasis

Secreted fromthyroid glands in response to high calcium levels in plasma

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What does Vit D do in calcium homeostasis

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

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How is calcitriol produced

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

How is Vitamin D3 produced

Dietary Vit D combines with 7-dehydrocholesterol synthesised in skin

How does calcitriol act in calcium homeostasis

INTESTINE:
-Calcium absorption

KIDNEY:
-Calcium retention
-Phosphate retention

BONE:
-Calcium release
-Phosphate release

OVERALL - increased levels of calcium and phosphate in plasma

What hormones decrease bone mass while increasing bone resorption

-Cortisol
-Parathyroid hormone
-Thyroid hormone

What hormones increase both bone formation and bone mass

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

What are osteocytes

Trapped osteoblasts in the bone matrix

What do osteoblasts produce

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

How do osteocytes contact other cells

Via long cytoplasmic processes

Where in the bone do osteocytes lie

Within the bony lacunae

Where would osteoclasts be found

Lie in depressions (Howship's lacunae)

What is hypercalcaemia

Raised calcium levels

What is hypocalcaemia

Reduced calcium levels

How does hypocalcaemia occur

Decreased calcium intake Excessive calcium loss Alkalosis (low calcium)

What can low calcium levels cause

Increased nerve excitability: ‘pins and needles’; muscle spasms, Trousseau’s sign; Chvostek’s sign

What can cause alkalosis

Hyperventilation such as a panic attack

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

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

What is Osteitis fibrosa cystica

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

Why does a Vit D deficiency cause rickets

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

What are 2 types of bone diseases

Osteoporosis: -Decreased bone mass and density Osteopetrosis -Increased bone mass and density

What is osteoporosis and it's symptoms

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)

What causes osteoporosis

Lack of plasma Calcium levels Corticosteroids Nutritional deficiency

What is osteopetrosisand it's symptoms

Increased bone density Reduced blood supply Prone to fracture and chronic infection Difficult extractions Tooth roots indistinct on radiographs Mandible > maxilla