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Structure & Function 6 > Calcium Regulation > Flashcards

Calcium Regulation Flashcards

1
Q

what is calcium important for?

A

muscle contraction
neuronal activity
exocytosis
coagulation of blood
communication between cells
structural integrity of bone
and more

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2
Q

intracellular calcium?

A

bound to proteins or within mitochondria/ER

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3
Q

describe the calcium found in bone?

A

hydroxyapatite crystals = calcium, phosphate and water

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4
Q

blood calcium is found in three forms - what are these?

A

bound to proteins (albumin) - 40%
complexed to anions (carbonate, citrate etc) - 10%
free ionised Ca2+ - 50%

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5
Q

canalicuculi?

A

connect osteocytes and osteoblasts

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6
Q

extracellular fluid importance for calcium?

A

important for control of calcium levels in blood
blood calcium and bone calcium pool (in solution)

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7
Q

what are the calcium-regulating hormones?

A

parathyroid hormone (PTH)
Vitamin D
Parathyroid hormone related peptide (PTHrP)
Calcitonin

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8
Q

two type of calcium store in bone - what are these?

A

readily exchangeable (0.1-1%)
slowly exchangeable (99%) - stable pool

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9
Q

Phosphate is controlled by what?

A

by the same systems that control calcium

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10
Q

where is phosphate absorbed from?

A

Intestines

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11
Q

where is phosphate stored?

A

in bone pools

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12
Q

where is phosphate excreted from?

A

from kidneys

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13
Q

what provides ready source of phosphate?

A

inorganic phosphate
acts as a buffer in the blood (maintain correct pH)

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14
Q

What is phosphate important for?

A

structure of boned and teeth
cell membranes (phospholipids)
DNA synthesis (sugar phosphate backbone)
ATP!

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15
Q

what is phosphate mainly regulated by?

A

kidney

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16
Q

what reabsorb 80-90% of filtered phosphate?

A

the renal tubules
close to renal threshold

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17
Q

what happens if dietary phosphate increases - renal?

A

exceeds renal threshold and excreted in urine

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18
Q

what does PTH decrease?

A

decreases renal reabsorption of phosphate thus increasing excretion
PTH decreases Na/P transporters

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19
Q

parathyroid gland?

A

main organ controlling central calcium and phosphate metabolism
four small nodules associated with the thyroid gland

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20
Q

describe the parathyroid gland histology and what cells we see?

A

Chief or Principal cells
- darker staining active cells secrete PTH
- lighter staining inactive cells - increase in number as animal ages
Oxyphil cells - not present in vet species
in humans
large and much lighter staining cells - unknown function

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21
Q

what is PTH secreted by and where is it metabolised and what is the action of PTH?

A

secreted by exocytosis
rapidly metabolised by liver and kidneys
acts to increase the ECF concentration of calcium

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22
Q

long-term calcium deficits?

A

when dietary uptake is low, calcium and phosphate is released from bone pools
PTH and vitamin D important for correction

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23
Q

if loss of calcium in ECF exceeds amounts available from bone pools, what does it lead to?

A

clinical signs of:
inappetence
ataxia (loss of co-ordination)
paresis (partial paralysis/weakness)
tetany (locked muscles)

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24
Q

describe the rapid exchange of calcium in the soluble portion of bone:

A

consists of crystals and soluble calcium
located in canaliculi between osteoblasts and osteocytes
These cells can mobilise calcium to the blood quickly

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25
describe the slow exchange of calcium to the bone:
small movements bone remodelling growing animals transfer more calcium into stable store than adults do
26
when the free calcium in the plasma is low describe the rapid exchange of calcium:
Ca2+ is transported from the bone fluid to plasma by PTH stimulated pumps in osteocytes
27
when the free calcium in the plasma is low describe the slow exchange of calcium:
PTH increases osteoclast activity, but Ca2+ is transported by PTH independent process
28
when the free calcium in the plasma is high describe the rapid exchange of calcium:
opposite occurs so the Ca2+ is transported from the plasma to the bone fluid
29
when the free calcium in the plasma is high describe the slow exchange of calcium:
osteoclast activity decreases
30
Where is there continual movement of calcium?
continual movement between the extracellular fluid, the bone, GI tract and kidneys
31
where is calcium absorbed?
GI tract Different requirements depending on life stage
32
Describe the excretion of calcium?
controlled by kidneys most of the calcium passing through the kidneys is reabsorbed Loss is matched by dietary absorption Distal tubules are under hormonal control
33
where is free calcium filtered, describe what type of calcium is not filtered?
it is filtered at the glomerulus whereas protein bound calcium is not
34
normally, how much filtered calcium is reabsorbed?
normally 96-98% of filtered calcium is reabsorbed
35
where does the majority of calcium excretion and reabsorption occur?
mostly (70%) occurs in the proximal convoluted tubule paracellularly secondary to osmosis
36
where is the remaining calcium reabsorbed?
in the distal convoluted tubule and convoluted tubule transcellularly via calcium channels in apical membrane and pumps on the basolateral membrane
37
what mediates DCT and CD absorption?
mediated by parathyroid hormone (PTH) - controllable calcium excretion
38
what is calcium regulated according to?
according to need
39
why is it essential that calcium remains low?
so calcium is bound to a protein during transport across the cell from apical to basolateral side
40
what is directly affected by the parathyroid hormone?
bone and kidney
41
what is indirectly affected by the parathyroid hormone?
GI tract
42
what are the several forms of vitamin D?
vitamin D2 and vitamin D3
43
what synthesises vitamin D2?
synthesised by plants
44
what synthesis vitamin D3?
by animals
45
what must vitamin D be activated by?
must be activated by additions of hydroxyl (OH) groups
46
what is step 1 of vitamin D synthesis and where does this occur?
occurs in liver 25-hydroxylase adds 1st OH group to Vit D Calcidiol - inactive (storage)
47
Where does step 2 of vitamin D synthesis occur?
in the kidney
48
describe step 2 of vitamin D synthesis when calcium levels normal:
24-hydroxylase adds 2nd OH group 24,25(OH)2 - vitamin D Inactive (excreted)
49
describe step 2 of vitamin D synthesis when calcium levels low:
PTH (parathyroid hormone) stimulates 1α-hydroxylase Calcitriol (1,25(OH)2 - vitamin D) Active - increases GI tract absorption of calcium
50
what does calcitriol do?
it increases calcium uptake from the small intestine
51
how does calcitriol increase uptake of calcium from the small intestine?
binds to nuclear vitamin D receptor upregulates Apical Ca2+ channels (e.g. TRPV5) Basolateral Ca2+ pumps (e.g. PMCA1b) Ca2+ transporter protein calbindin - D9K Increase transcellular calcium absorption from small intestine
52
what is calcitonin produced by?
produced by parafollicular cells (also called C-cells) in the thyroid gland
53
what does calcitonin act to reduce?
acts to reduce calcium and phosphate
54
what does calcitonin decrease the movement of?
decreases movement of ions from bone pools to the extracellular fluid
55
what does calcitonin inhibit?
inhibits osteoclasts - decreased bone resorption
56
what does calcitonin increase?
increases renal excretion of calcium and phosphate
57
what mechanism is responsible for the control of calcitonin and PTH secretion?
negative feedback mechanism
58
what causes an increase in calcitonin secretion?
GI hormones gastrin, CCK (cholecystokinin) and secretin all increase calcitonin secretion
59
what does parathyroid hormone-related peptide (PTHrP) have a similar structure to?
similar in structure to PTH
60
what is PTHrP?
parathyroid hormone-related peptide
61
where is PTHrP produced?
produced in most tissues of the body
62
what receptor does PTHrP bind to?
binds to the same receptor as PTH (g-protein coupled) so has same effects
63
what other receptors does PTHrP bind to?
PTHrP also binds to other receptors not activated by PTH - diverse effects
64
when PTHrP binds to its 'other receptors' - what happens?
plays role in proliferation, differentiation and apoptosis Important for regulation of placental transport of calcium to foetus and transfer of calcium from blood to milk
65
what is hypercalcaemia?
certain types of cancers produce PTHrP leading to increases levels of calcium No negative feedback mechanisms so leads to hypercalcaemia Can measure serum PTHrP as a useful diagnostic tool in differential diagnosis
66
what are eggshells mainly made up of?
calcium carbonate
67
where are eggshells produced?
in the shell gland
68
what part of the egg contain high levels of phosphate?
yolk and egg white
69
what is required in the diet for hens to continue laying eggs?
continuous dietary supply of calcium eggshells are 10% of skeletal calcium
70
what is a pullet?
a young hen
71
what accumulates in pullets to aid with egg laying when older?
extra medullary bone accumulates in pullets prior to start of egg-laying as mature adults to increase the available bone pool of calcium
72
when shell synthesis begins - concentration of what falls?
extracellular fluid concentration of Ca2+ ions falls
73
how does PTH affect [Ca2+] in ECF?
PTH works to increase blood calcium levels by stimulating calcium release from bone and enhancing calcium reabsorption in the kidneys and intestines
74
how does Clacitriol affect [Ca2+] in ECF?
calcitonin acts to lower blood calcium levels by promoting calcium deposition into bones
75

Structure & Function 6 (19 decks)

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