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Endocrinology > Calcium Homeostasis > Flashcards

Calcium Homeostasis Flashcards

1
Q

list the roles of calcium in the body

A
  1. signalling (synaptic vesicles, neurotransmitters. muscle contraction)
  2. blood clotting
  3. apoptosis
  4. skeletal strength
  5. membrane excitability
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2
Q

what effect does calcium have on Na permeability

A

calcium decreases Na permeability

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3
Q

why is there hyperexcitation of neurons in hypocalcaemia

A

as calcium decreases Na permeability, if there is less calcium present then this increases neuronal Na permeability

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4
Q

what effect does hypercalcaemia have on neuronal Na permeability

A

hypercalcaemia decreases neuronal Na permeability which will reduce excitability and depress neuromuscular activity

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5
Q

were is 99% of calcium in our body

A

in our bones

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6
Q

apart from our bone where else is calcium stored in the body

A
  1. 9% in intracellular fluid (mostly inside mitochondria and sarcoplasmic reticulum)
  2. 1% in extracellular fluid (nearly half of ECF Ca is bound to protein)
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7
Q

what form is calcium stored in the bone

A

hydroxyapatite (Ca10(PO4)6(OH)2)

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8
Q

calcium has a very high affinity for proteins why is this

A

as it is a small positive charge it will be attracted to large negative charge such as proteins

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9
Q

in plasma how much of total calcium present is bound to plasma proteins

A

40% is bound to plasma proteins

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10
Q

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?

A

Albumin 80%

Globulin 20%

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11
Q

what percentage of calcium in the blood is free(ionised)

A

50%

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12
Q

free(ionised) calcium can form complexes with what

A

can form complexes with free anions to give for example, calcium carbonate

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13
Q

what is an anion

A

a negatively charged ion

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14
Q

the binding capacity of plasma proteins change with pH true or false

A

true

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15
Q

in relation to pH when does the binding capacity of plasma proteins increase

A

binding capacity is increased under alkalotic conditions

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16
Q

what effect does alkalosis have on protein bound calcium

A

alkalosis increases protein bound calcium

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17
Q

what effect does acidosis have on protein bound calcium

A

acidosis decreases protein bound calcium therefore free [Ca2+]plasma rises

18
Q

the calcium in bone can be added to or released as required true or false

A

true

19
Q

what are osteoblasts

A

known as the bone building cells, they are the cells that form new bone

20
Q

what do osteoblasts differentiate into

A

osteocytes

21
Q

what do osteocytes do

A

they are much less active than osteoblasts, they regulate the activity of osteoblasts and osteoclasts

22
Q

what are osteoclasts

A

is a type of bone cell that breaks down bone tissue by secreting H+ ions and proteolytic enzymes to dissolve ECM

23
Q

two key hormones act to increase [Ca2+]plasma what are they

A 
parathyroid hormone (PTH)
calcitriol(active form of Vit D)
24
Q

what is parathyroid hormone and where is it produced

A

it is a polypeptide hormone produced by the parathyroid glands

25
Q

what is Calcitriol and where is it produced

A

it is a steroid hormone and it produced from vitamin D by the liver and kidneys

26
Q

where would you find the parathyroid glands

A

lying on the posterior surface of the thyroid gland

27
Q

what triggers the release of parathyroid hormone

A

it is released in response to a decrease in free {Ca2+] plasma

28
Q

what is the general function of parathyroid hormone

A

acts to increase free [Ca2+]plasma

29
Q

how does PTH act to increase free [Ca2+]plasma

A
  1. stimulates osteoclasts to increase resorption of Ca2+ and phosphate in bone
  2. inhibits osteoblasts to reduce Ca2+ deposition in the bone
  3. increases reAbsorption of Ca2+ from the kidney tubules therefore decreasing its excretion in urine
  4. increasing renal excretion of phosphate as phosphate is needed to deposit Ca2+ back in bone
  5. stimulates the kidney to synthesise calcitriol from vitamin D which promotes calcium absorption at the gut and kidney
30
Q

prolactin stimulates calcitriol formation in lactating women true or fasle

A

true

31
Q

what is active vitamin D formed from

A

cholesterol derivatives (this happens by the action of UV light on the skin)

32
Q

what are the target tissues of Calcitriol

A

intestine
bone
kidney

33
Q

what is the effect of calcitriol when it binds to nuclear receptors in target tissues

A
  1. increases absorption of Ca2+ from the gut
  2. facillitates renal absorption of Ca2+
  3. mobilises calcium stores in bone by stimulating osteocclast activity

collectively it INCREASES [Ca2+]plasma

34
Q

what is considered to be the direct effect of vitamin D3

A

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+

35
Q

why do bones get soft in vitamin D deficiency

A

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

36
Q

what is the only hormone that acts to decrease Ca2+ plasma levels

A

calcitonin

37
Q

what is calcitonin

A

peptide hormone that acts to decrease calcium levels in the plasma

38
Q

where is calcitonin produced from

A

thyroid gland

39
Q

what is the mechanism by which calcitonin decreases plasma Ca+

A

binds to osteoclasts and inhibits bone resorption

increases renal excretion of Ca2+

40
Q

what is the effect of insulin on bone formation

A

increases bone formation (diabetics have significant bone loss)

41
Q

what is the effect of oestrogen on bone formation

A

promotes bone formation via oestrogen receptors on osteoblasts (post-menopausal osteoporosis)

42
Q

what is the effect of growth hormone on bone formation

A

GH is a constant stimulus for bone formation

Endocrinology (25 decks)

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