Calcium Homeostasis Flashcards
list the roles of calcium in the body
- signalling (synaptic vesicles, neurotransmitters. muscle contraction)
- blood clotting
- apoptosis
- skeletal strength
- membrane excitability
what effect does calcium have on Na permeability
calcium decreases Na permeability
why is there hyperexcitation of neurons in hypocalcaemia
as calcium decreases Na permeability, if there is less calcium present then this increases neuronal Na permeability
what effect does hypercalcaemia have on neuronal Na permeability
hypercalcaemia decreases neuronal Na permeability which will reduce excitability and depress neuromuscular activity
were is 99% of calcium in our body
in our bones
apart from our bone where else is calcium stored in the body
- 9% in intracellular fluid (mostly inside mitochondria and sarcoplasmic reticulum)
- 1% in extracellular fluid (nearly half of ECF Ca is bound to protein)
what form is calcium stored in the bone
hydroxyapatite (Ca10(PO4)6(OH)2)
calcium has a very high affinity for proteins why is this
as it is a small positive charge it will be attracted to large negative charge such as proteins
in plasma how much of total calcium present is bound to plasma proteins
40% is bound to plasma proteins
in the blood 40% of calcium is bound to protein, of this 40% how much is bound to albumin? how much is bound to globulin?
Albumin 80%
Globulin 20%
what percentage of calcium in the blood is free(ionised)
50%
free(ionised) calcium can form complexes with what
can form complexes with free anions to give for example, calcium carbonate
what is an anion
a negatively charged ion
the binding capacity of plasma proteins change with pH true or false
true
in relation to pH when does the binding capacity of plasma proteins increase
binding capacity is increased under alkalotic conditions
what effect does alkalosis have on protein bound calcium
alkalosis increases protein bound calcium
what effect does acidosis have on protein bound calcium
acidosis decreases protein bound calcium therefore free [Ca2+]plasma rises
the calcium in bone can be added to or released as required true or false
true
what are osteoblasts
known as the bone building cells, they are the cells that form new bone
what do osteoblasts differentiate into
osteocytes
what do osteocytes do
they are much less active than osteoblasts, they regulate the activity of osteoblasts and osteoclasts
what are osteoclasts
is a type of bone cell that breaks down bone tissue by secreting H+ ions and proteolytic enzymes to dissolve ECM
two key hormones act to increase [Ca2+]plasma what are they
parathyroid hormone (PTH) calcitriol(active form of Vit D)
what is parathyroid hormone and where is it produced
it is a polypeptide hormone produced by the parathyroid glands
what is Calcitriol and where is it produced
it is a steroid hormone and it produced from vitamin D by the liver and kidneys
where would you find the parathyroid glands
lying on the posterior surface of the thyroid gland
what triggers the release of parathyroid hormone
it is released in response to a decrease in free {Ca2+] plasma
what is the general function of parathyroid hormone
acts to increase free [Ca2+]plasma
how does PTH act to increase free [Ca2+]plasma
- stimulates osteoclasts to increase resorption of Ca2+ and phosphate in bone
- inhibits osteoblasts to reduce Ca2+ deposition in the bone
- increases reAbsorption of Ca2+ from the kidney tubules therefore decreasing its excretion in urine
- increasing renal excretion of phosphate as phosphate is needed to deposit Ca2+ back in bone
- stimulates the kidney to synthesise calcitriol from vitamin D which promotes calcium absorption at the gut and kidney
prolactin stimulates calcitriol formation in lactating women true or fasle
true
what is active vitamin D formed from
cholesterol derivatives (this happens by the action of UV light on the skin)
what are the target tissues of Calcitriol
intestine
bone
kidney
what is the effect of calcitriol when it binds to nuclear receptors in target tissues
- increases absorption of Ca2+ from the gut
- facillitates renal absorption of Ca2+
- mobilises calcium stores in bone by stimulating osteocclast activity
collectively it INCREASES [Ca2+]plasma
what is considered to be the direct effect of vitamin D3
to release Ca2+ from the bone
(its affects on Ca2+ absorption from the gut/reabsorption at the kidneys means the net effect is to INCREASE plasma Ca2+
why do bones get soft in vitamin D deficiency
as PTH has to work hard to maintain plasma Ca2+ levels
therefore it has to keep removing Ca2+ from the bone
this results in bones that are soft and prone to fracture in adults
what is the only hormone that acts to decrease Ca2+ plasma levels
calcitonin
what is calcitonin
peptide hormone that acts to decrease calcium levels in the plasma
where is calcitonin produced from
thyroid gland
what is the mechanism by which calcitonin decreases plasma Ca+
binds to osteoclasts and inhibits bone resorption
increases renal excretion of Ca2+
what is the effect of insulin on bone formation
increases bone formation (diabetics have significant bone loss)
what is the effect of oestrogen on bone formation
promotes bone formation via oestrogen receptors on osteoblasts (post-menopausal osteoporosis)
what is the effect of growth hormone on bone formation
GH is a constant stimulus for bone formation
