Calcium Flashcards
What are the functions of calcium
- bone and tooth structure
- mineral store
- action potentials (cardiac muscle)
- membrane excitability
- 2nd messenger
- co-factor in metabolic pathways
- blood clotting
Give examples of how calcium acts as a second messenger
- muscle excitation-contraction coupling
- gland secretion
- non-steroid hormone action
Describe parathyroid secretion
Secreted from parathyroid glands in response to low plasma (Ca2+)
Acts to increase plasma calcium by:
- increase bone (osteoclasts)
- increase calcium response in kidney (with decreased oxygen reabsorption)
- increased uptake of Ca 2+ from the intestines
When is parathyroid hormone secreted
Secreted from parathyroid glands in response to low plasma Ca2+
How does calcitonin act to lower plasma calcium
Increased formation of bone (osteoblasts)
Decreased calcium resorption in kidney
Describe diffusible calcium concentration
Ionised calcium 1.2mmol/l
Bound to citrate 0.2mmol/l
What is the calcium concentration of non diffusible calcium
1.2mmol/l
What is the calcium concentration of blood plasma
2.6mmol/l
Name some functions of calcium
- bone and tooth structure
- mineral store
- action potentials (cardiac muscles)
- membrane excitability
What is the role of calcium in muscles
Responsible for excitation contraction coupling
What are some ways calcium can be obtained in the body
- diet
- kidneys
- exchangeable bone
What hormones control calcium homestasis
- parathyroid hormone
- calcitonin
- vitamin D
What is the role of parathyroid hormone in calcium secretion
- secreted from parathyroid glands in response to low plasma (Ca2+)
- acts to increase plasma calcium by - increasing osteoclastogenesis, increasing calcium Reabsorption by kidney and increasing uptake of calcium from the intestines (assisted by vitamin D)
What is the role of calcitonin
- secreted from the thyroid glands in response to high plasma (Ca2+)
- acts to lower plasma calcium by increased osteoblastogenesis, decreased calcium resabsorption by the kidneys
Does not seem to play a massive role, no pathological effects
What ways can vitamin D3 be obtained
- diet
- 7-dehydrocholestrol synthesised in the skin
What is cholecalciferol
Vitamin D3 essential for the deposition of calcium in the bones and formed by the action of sunlight on the de hydro Cholestrol in the skin
What happens to cholecalciferol in the kidney
Cholecalciferol converted into calcitrol in the kidney, this is regulated by PTH
What effect does calcitrol have on the intestine
Increased calcium absorption
What effect does calcitrol have on the kidney
Ca retention and PO4 retention of the kidney
What effect does calcitrol have on bone
Ca release and PO4 release
What overall effect does calcitrol have on the body
Increased levels of calcium and phosphate in the plama
Name some hormones that increase bone formation and bone mass
- calcitonin
- growth hormone
- insulin
- IGF-1
- Oestrogen
- Testosterone
Name some hormones that increase bone reabsorption and decrease bone mass
- cortisol
- parathyroid hormone
- thyroid hormones
Where do osteoclasts lie in the bone
Lie in depressions known as howships lacunae
What is hypercalcaemia
Raised calcium levels
What is hypocalcemia
Reduced calcium levels
What is hypocalcemia caused by
- decreased calcium intake
- excessive calcium loss
- alkalosis (low Ca2+)
A panic attack could cause this, excessive blowing off of CO2, rebreathing air from a bag can solve this
What are the effects of low calcium concentration
Increased nerve excitabity
- pins and needles, muscle spasms
- trousseaus sign, chvosteks sign
What can hyperparathyrodism cause
Osteitis fibrosa - areas of demineralisation in the skull and legs
What can hyperparathyroidism cause in the teeth
Defective mineralisation of teeth due to low blood calcium levels due to undersecretion of PTH
What can vitamin D deficiency cause
Rickets (children)
Osteomalacia (adults)
What is osteoporosis
Decreased bone mass and density, fractures are common, more common in elderly
What is osteopetrosis
Increased bone mass and density
Results in -
Reduced blood supply, fracture, chronic inflammation
What can osteopetrosis cause in terms of dentistry
Difficult tooth extraction
What is the term used to describe low calcium levels in the body
Alkalosis
