calcium Flashcards
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
what are the components involved in calcium homeostasis?
- parathyroid hormone
- calcitonin
- vitamin D
where is the parathyroid hormone secreted from?
parathyroid glands
what is the action which triggers the secretion of the parathyroid hormone?
low plasma Ca2+
what does the parathyroid to in response to low plasma Ca2+?
- increases reabsorption of bone (osteoclasts)
- increases calcium ion reabsorption in kidney
- increases uptake of calcium ions from the intestines (assisted by vit D)
what is a very important element in calcium turnover?
exchangeable bone
what is meant by exchangeable bone?
where is calcitonin secreted from?
the thyroid glands
what triggers the release of calcitonin by the thyroid glands?
high plasma Ca2+
how does calcitonin act in response to an increase in plasma Ca2+?
- increases formation of bone (osteoblasts)
- decreased calcium ion reabsorption in the kidney
vitamin D
which hormones increase both bone formation and bone mass?
- calcitonin
- growth hormone
- IGF-1
- insulin
- oestrogen
- testosterone
which hormones increase bone resorption and decrease bone mass?
- cortisol
- parathyroid hormone
- thyroid hormones
bone remodelling
what is hypercalcaemia?
raised Ca2+
what is hypocalcaemia?
reduced Ca2+
what is hypocalcaemic tetany?
a condition surrounding decreased Ca2+ due to:
- decreased intake
- excessive loss
- alkalosis (low Ca2+)
leads to increased nerve excitability:
- pins and needles
- muscles spasms
- trousseaus sign
- chvosteks sign
what is hyperventilation an example of?
hypocalcaemia
- panic attack can cause alkalosis by blowing off CO2
- treated by rebreathing expired air from bag
what is osteitis fibrosa cystica?
- results from hyperparathyroidism
- areas of demineralisation in skull and leg bones
what can result from hypoparathyroidism?
- defective mineralisation of teeth
what are the consequences of a vitamin D deficiency?
- decreased Ca uptake from GI tract
- unmineralised bone
- bone lacks rigidity
- rickets/osteomalacia
what is a condition in children associated with a vit D deficiency?
rickets
what is a condition in adults associated with a vit D deficiency?
osteomalacia
what are the effects of varying levels of calcitonin?
no obvious clinical consequences
what is osteoporosis?
decreased bone mass and density
- fractures common
- common in elderly
- more common in women
what is osteopetrosis?
increased bone mass and density
- reduced blood supply
- prone to fracture
- prone to chronic infection
- difficult extractions
