Bone minerals Flashcards
What are the 2 main functions of calcium?
99% is stored in bone and teeth - bone structure
1% is circulating in the blood and soft tissue - for muscle contraction and nerve impulses
How is blood calcium increased when calcium intake is low?
increased PTH is secreted from the parathyroid gland
PTH activates Vitamin D
Vitamin D stimulates:
- increased Ca renal absorption from kidneys
- increased Ca release into blood from bone demineralisation by osteoclasts
- increased Ca absorption in SI
How is blood calcium decreased when calcium is high?
Calcitonin is secreted from the thyroid gland
This inhibits Vitamin D activation
- decreases renal Ca reabsorption
- inhibits osteoclasts to decrease bone demineralisation
- decreases absorption in SI
What is hypocalcaemia caused by?
- low PTH
- vomiting
- anorexia
- excess mineral supplements (e.g. Zn, Mg)
What does hypocalcaemia cause?
Causes muscle twitching/spasms by inhibiting muscle contraction/relaxation
What is hypercalcaemia caused by?
- excess vitamin D (supplements)
- cancer
- increased PTH
What does hypercalcaemia cause?
Stiffening of muscles from failure of muscles to relax
How is calcium and dairy associated with preventing weight gain?
- decreases appetite and lipogenesis
- increases fat excretion, thermogenesis and lipolysis
How is calcium absorbed?
- active transport with Vitamin D, or passive diffusion
- absorbed in duodenum with acid which assists in its absorption
What is the maximum calcium absorption?
500mg/dose
Discuss the bioavailability of calcium in foods.
> 50% absorbed in cauliflower, broccoli, brussel sprouts
~30% absorbed in milk, dairy, yoghurt, fortified products
~20% absorbed in almonds, sweet potato
<5% absorbed in spinach, rhubarb due to oxalates
What inhibits/enhances calcium absorption?
Inhibits - oxalates, phytates, other minerals
Enhances - lactose
What is osteopenia?
a condition where bone mineral density is lower than normal - risk factor for osteoporosis
What is osteoporosis?
a condition where bone mineral density is much lower than normal
What are the risk factors for osteoporosis?
- low vitamin D and calcium
- menopause (bone loss)
- smoking and alcohol intake
- lack of physical activity
- medications
- low testosterone (men)
- family history
- low body weight
