Calcium Physiology Flashcards
what are the main functions of calcium
bone and tooth structure
mineral store
action potentials
membrane excitability
second messengers
co factor in metabolic pathways
blood clotting
describe the second messenger action of calcium
acts in:
muscle for excitation contraction coupling
gland secretion
non steroid hormone action
describe the concentration of ionised calcium
1.2mmol/litre
what is the concentration of calcium bound to citrate
0.2mmol/litre
what are the forms of diffusible calcium
ionised calcium and bound to citrate
what are the forms of non diffisuble calcium
bound to protein
what is the concentration of calcium bound to protein
1.2mmol/litre
what is the total calcium concentration
2.6 mmol/litre
which molecules are involved in calcium homeostasis
parathyroid hormone
calcitonin
vitamin D
describe parathyroid hormone secretion
produced from the parathyroid gland in resopnse to low plasma calcium concentration
how does parathyroid hormone increase plasma calcium
- increase resorption of bone through osteoclast activity
- increase calcium resorption in the kidneys with a decrease in phosphate resorption
- increased uptake of calcium from the intestines, with the assistance of vitamin D
what happens in the kidneys to increase plasma calcium concentration
increased formation of calcitriol (active vitamin D)
increased calcium resorption
increased phosphate excretion
what is 1.25 hydroxyvitamin D
this is the most active form of vitamin D known as calcitriol
describe calcitonin secretion
produced from thyroid glands in resopnse to high plasma calcium concentration
how does calcitonin act
lowers plasma calcium by increases the formation of bone through osteoblastogenesis and a decrease in calcium resorption in the kidney
does calcitonin play a role in calcium homeostasis
not a major one
what is the form of vitamin D formed in the skin from UV
7-dehydrocholesterol
what is vitamin D3
cholecalciferol, formed from dietary vitamin D and 7-dehydrocholesterol
describe vitamin D production
- diet and skin provide two forms
- 7-hydrocholesterol in the skin
- come together to form vitamin D3
- this goes to liver and is acted upon by 25-hydroxylase
- to form 25 hydroxy cholecalferol
- this is acted upon in the kidney by 1alpha hydrolyase
- this forms calcitriol
describe the destination of calcitriol
intestines for calcium absorption
kidney for calcium retentin and phosphate retention
bone for calcium and phosphate release
which hormones increase bone formation and bone mass
calcitonin
growth hormone
IGF
insulin
oestrogen
testosterone
which hormones decrease bone mass through increasing bone resorption
cortisol
parathyroid homrone
thyroid hormones
what do osteoblasts do
they synthesis and secrete collagen fibres forming a matrix later mineralised by calcium salts
what are osteocytes
these are trapped osteoblasts in the bone matrix
they lie within bony lacunae and contact other cells via long cytoplasmic processes
what are osteoclasts
large, multinucleated cells derived from macrophages, that resorb bone
where do osteoclasts lie in bone
howships lacunae
desribe hypocalcaemic tetany
this is a decrease in calcium concentration due to decreased intake, excessive loss, or alkalosis
leads to low nerve excitability, causing muscle spasms, pinks and needles and trousseaus sign
what is alkalosis
low calcium concentration
what is hypocalcaemia
this is caused from hyperventilation, as in panic attacks which can cause alkalosis
happens due to blowing off carbon dioxide
what is osteitis fibrosa cystica
areas of demineralisation in the skull and leg bones
what can hypoparathyroidism do to the teeth
lead to defective mineralisation of teeth due to low blood calcium levels due to undersecretion of parathyroid hormone
what can cause vtiamin D deficiency
dietary deficiency, or a failure to synthesise in the body
what does vitamin D deficiency do to the body
decreases calcium uptake from the gastrointestinal tract
leads to undermineralised bone
leads to unmineralised bone lacking rigidity
what does vitamin D deficiency cause in children
rickets
what does vitamin D deficiency cause in adults
osteomalacia
what is osteoporosis
decreased bone mass and density
what is osteopetrosis
increased bone mass and density
describe osteoporosis in patients
reduced bone dentistry due to a loss of matric and mineral leads to fractures
common in the elderly, particularly women
what are the causes of osteoporosis
nutritional deficiency and corticosteroids
describe osteopetrosis in patients
increased bone density leads to reduced blood supply
bones are prone to fracture and chronic infection
makes extractions difficult
mandible is larger than maxilla
