Lecture 25: Calcium Metabolism Flashcards
(40 cards)
how is calcium homeostasis maintained
tightly regulated ion transport by GIT, bone and kidneys
what % of total plasma Ca2+ is free
50%
which form of Calcium is metabolically active and has biological effects
ionised (free) calcium
list the molecules that calcium binds to in the plasma
- anions
- albumin
- globulin
what are the 2 variables that affect the proportion of calcium that is free or bound
- albumin conc.
- blood pH
how does pH affect the proportion of free or bound plasma Ca2+
- H+ ions also bind to albumin
- H+ can displace Ca2+
- iCa2+ ^
name the 3 hormones that act to regulate Ca2+ homeostasis
- parathyroid hormone (parathormone)
- activated Vit D
- calcitonin
what are the 2 other names for activated Vit D
- -> 1,25-dihydroxycholecalciferol
- -> calcitriol
what stimulates release of parathyroid hormone
- low Ca2+
- ^ phosphate
- low Mg2+
name the cells on parathyroid glands that detect low calcium levels
chief cells
describe the action of parathyroid hormone in Ca2+ homeostasis
main role is to ^ Ca2+ levels in the blood
Bone
- short term: rapid exchange from bone pool to ECF
- long term: resorption by osteoclasts
Kidney
- reabsorption of Ca2+
- excretion of phosphate (reciprocal relationship)
- formation of 1,25-dihydroxycholecalciferol
Intestine
- Ca2+ reabsorption
name regulators for active Vit D
- PTH
- low phosphate
what type of hormone is Vit D
steroid hormone –> derived from cholesterol
name the main enzyme involved in Vit D activation in the kidneys
1 a-hydroxylase
describe the action of activated Vit D in Ca2+ homeostasis
Intestine
- ^ Ca2+ absorption
- ^ Ca2+ transport prots –> calbindin-D prots
Kidneys
- facilitates Ca2+ absorption
Bone
- ^ calcification and mineralisation
what mediates Vit D action
- receptors
- Vit D is a steroid hormone w/ genomic effects
- binds to receptor on nucleus
describe the difference between rickets and osteomalacia
rickets = Vit D deficiency in child
osteomalacia = Vit D deficiency in adult
list some causes of rickets and osteomalacia
- lack of dietary Vit D and/or sunlight
- malabsorption of fats
- failure to form calcitriol –> chronic renal failure
- mutation in 1 a-hydroxylase
- mutations in VDR
what are the 4 fat soluble vitamins
A,D,E,K
outline a basic difference between osteoporosis and osteomalacia
osteoporosis = normal bone just not enough
osteomalacia = abnormal soft bone which hasn’t been mineralised
what people are at risk of Vit D deficiency
- elderly people
- house-bound people
- those who cover up a lot in the sun
- those who where sunscreen all year
- those with dark skin
why are people with dark skin at risk of Vit D deficiency
- they require more sun exposure to make as much Vit D
- sunlight needs to penetrate through layer of melanin to layer that manufactures Vit D
where is calcitonin produced
in thyroid gland by C cells
name a regulator of calcitonin secretion
^ Ca2+
