calcium disorders Flashcards
(48 cards)
1
Q
is calcium the most abundant mineral in the body
A
yes
2
Q
what is the dietary calcium intake
A
25mmol/day
3
Q
how much dietary calcium is lost and via what
A
20mmol/day in faeces
4
Q
how much calcium does bones have
A
25,000mmol
5
Q
how much calcium does extracellular fluid have
A
23mmol
6
Q
how much calcium does plasma have
A
9mmol
7
Q
how much calcium is taken in by kidneys and reabsorbed back into plasma
A
240mmol/day taken into kidney and 235mmol/day reabsorbed back. therefore, 5mmol/day of calcium is lost via renal loss
8
Q
functions of calcium
A
- strength- bones, teeth
- nervous system- they release neurotransmitters
- muscles- they initiate muscle contractions
- cell adhesion- cadherins help cells attach to eachother
- hormonal- they are the intracellular second messenger
- enzymatic function- they are the coenzymes for coagulation factors
9
Q
how is calcium needed in muscle contraction
A
- action potential arrives at junction which causes the release of acetylcholine (neurotransmitter)
- they bind to receptors causing an action potential to occur and then calcium being released from sarcoplasmic reticulum
- for muscle contraction to occur the myosin head and actin need to interact
- the calcium binds to troponin causing a change (unblocks binding sites)
- therefore, actin and myosin heads interact causing contraction
10
Q
how does muscle relaxation occur
A
- the calcium detaches from the troponin and enters back into sarcoplasmic reticulum (via ATP)
11
Q
what type of systems is calcium needed for
A
- first phase of embryonic development
(fertilisation) - nervous system
- for insulin secretion
12
Q
what are the different forms of calcium
A
- free ionised calcium (47%)
- protein bound (46%)
- complexed calcium (7%)
13
Q
describe free ionised calcium
A
- its physiologically active
- its regulated by homeostatic mechanisms
14
Q
what is the normal calcium reference range
A
- total calcium- 2.20-2.60 mmol/L
- free ionised calcium- 1.20-1.37 mmol/L
15
Q
what are the factors affecting calcium concentration
A
- changes in albumin (plasma protein) concentration
- changes in anion concentration
- changes in acid-base (pH)
16
Q
what type of calcium changes when there are changes in albumin
A
total calcium (2.20-2.60mmol/L)
17
Q
what type of calcium changes when there are changes in anion conc and acid base abnormalities
A
free ionised calcium (1.20-1.37mmol/L)
18
Q
describe what happens when there are changes in plasma proteins (albumin)
A
- when there is decreased albumin there is less total calcium but the free ionised calcium doesn’t change.
- this could be due to liver disease, malnutrition, nephrotic syndrome
- when there is increased albumin the total calcium increases but the free ionised calcium doesn’t change
- this is due to severe dehydration, infections
19
Q
what is the equation for correction factor
A
- if the albumin is less than 40 then:
total calcium measured + (0.02 x (40-albumin)) - if the albumin is more than 40 then:
total calcium measured - (0.02 x (albumin-45))
20
Q
describe changes in anion concentration
A
- when anion (phosphate) concentration decreases (hypophosphatemia) then the free ionised calcium concentration increases
- this is due to vitamin d deficiency and diuretic therapy
- when anion concentration (phosphate) increases (hyperphosphatemia) then free ionised concentration decreases
- this is due to vitamin d intoxication, renal failure and hypoparathyroidism
21
Q
describe changes in pH- acid base imbalance
A
- when there is acidosis (low pH and high H+ ions) there is high free ionised calcium but the total calcium stays the same
- when there is alkalosis (high pH and low H+ ions) there is low free ionised calcium but the total calcium stays the same
22
Q
what are the hormones that regulate calcium homeostasis
A
- parathyroid hormone
- calcitonin
- calcitrol
23
Q
how is the parathyroid hormone synthesised
A
- there is pre-pro-PTH which has 115 amino acids which then undergoes synthesis in the rough endoplasmic reticulum to for pro-PTH (90 amino acids)
- pro-PTH then is processed in the golgi apparatus to form PTH (84 amino acids)
- PTH is then packaged into parathyroid granules and released when calcium levels are low
24
Q
what fragment is on the PTH
A
- N-terminal which is biologically active
- c-terminal
25
what is needed for the secretion of PTH from the granules
magnesium
26
describe the synthesis of calcitriol
- our skin has 7-dyhydrolcholesterol (provitamin D) and when sunlight hits our skin it converts it into previtamin D3
- this converts into cholecalciferol (vitamin D3)
- cholecalciferol (vitamin D3) then goes into the liver where an enzyme called 25 hydroxylase helps convert it into 25-hydroxylcholecalciferol
- a dietary intake of vitamin D3 (fish) and vitamin D2 (supplements) goes into the liver
- 25-hydroxylcholecalciferol then goes into the kidney where another enzyme called 1 hydroxylase convert it into 1,25-dihydroxycholecalciferol (calcitriol)
- PTH also helps in the kidneys to convert into calcitriol
27
what are the functions of calcitrol
- increases calcium and phosphate absorption in the gut
- increases renal tubular reabsorption of calcium
- increases bone reabsorption (osteoclasts)
- inhibits calcitonin
28
when calcitriol binds to the calcitrol binding receptors in the small intestine what happens
it increases calcium binding protein and calcium transport into blood
29
what inhibits calcitonin
calcitriol
30
what will happen to the calcium regulation if there is no magnesium to secrete PTH
calcium regulation will be disrupted as magnesium is needed to release PTH
31
what is the function of PTH in the body
- bone: it increases osteoclast (breakdown bone) activity which therefore releases calcium into the plasma
- kidney: increases calcium reabsorption and the production of 1,25-dihydroxycholecalciferol (calcitriol). decreases phosphate and bicarbonate reabsorption
- intestines: increases calcium absorption. this is because it stimulates the production of calcitriol which binds to the intestine
32
what is the function of 1,25-dihydroxycholecalciferol (calcitriol)
- goes into gastrointestinal tract (GIT) and increases the absorption of calcium
- helps calcium being released from the bones
- also calcium reabsorption in the kidneys
33
what is calcitriol (1,25-dihydroxycholecalciferol) derived from
from vitamin D
34
what makes the synthesis of 1,25-DHCC become activated
- increased PTH
- decreased phosphate
- decreased calcium
35
what happens to 25-hydroxycholecalciferol when there are normal or high concentrations of calcium in the plasma
the enzyme 24-hydroxylase acts upon 25-hydroxycholecalciferol which leads to the formation of 24,25-dihydroxycholecalciferol which is an inactive form of calcitriol
36
where is calcitonin synthesized
in the c cells of the thyroid gland
37
what is calcitonin composed of
32 amino acid peptides
38
what causes calcitonin to be released
when there is an increase in calcium
39
what inhibits calcitonin from being released
when there is a decrease in calcium
40
what is the function of calcitonin
opposite to PTH
- stops calcium from being released from the bone
- stops calcium from being reabsorbed in the kidneys
- decreases calcium absorption in the gut
41
what type of conditions can people have for calcitonin to be prescribed
- hypercalcaemia
- osteoporosis
42
what is the disorder called when you have low plasma calcium concentration
hypocalcaemia
43
what is the disorder called when you have high plasma calcium concentration
hypercalcaemia
44
describe what happens to different organs in body when there's hypercalcaemia
- increased absorption of calcium in the GIT
- decreased renal extraction of calcium (absorb more calcium)
- increased bone loss (osteoclats) so more calcium will be absorbed
45
what are the causes of increased GIT absorption of calcium
- excessive vitamin D intake
- tuberculosis
- acromegaly (1-hydroxylase activity in kidneys)
these increase the calcitriol levels in the body
46
what causes a decrease in renal excretion of calcium
- thiazide diuretics (increased calcium reabsorption)
- milk-alkali syndrome
47
what causes an increase in bone loss (osteoclasts which leads to increased calcium reabsorption)
- malignancy
- primary hyperparathyroidism (overactive parathyroid gland = increased PTH released)
- hyperthyroidism (increased osteoclast activity = increased bone reabsorption)
48
what are the causes of hypocalcaemia
