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function of CNS and endocrine > 26 Hormonal regulation of calcium and phosphate balance > Flashcards

26 Hormonal regulation of calcium and phosphate balance Flashcards

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1
Q

what processes is calcium essential for

A
  • excitation-contraction coupling
  • stimulus-secretion coupling
  • blood coagulation
  • structural component of bone
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2
Q

where is most of the calcium in the body stored

A

in the bone

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3
Q

is phosphate essential for different phsyiology processes

A

yes its a required component of cellular structures and chemicals eg phospholipids

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4
Q

mechanisms regulating calcium and phosphate levels

A
  • absorption
  • deposition
  • reabsorption
  • excretion
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5
Q

what hormones regulate calcium and phosphate

A
  • parathyroid hormone (PTH)
  • 1,25-dihydroxyvitamin D
  • calcitonin
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6
Q

is parathyroid hormone a peptide hormone

A

yes

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7
Q

what secretes parathyroid hormone and in reponse to what

A

chief cells in response to low plasma calcium levels

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8
Q

regulation of PTH secretion

A
  1. calcium binds to CasR (calcium sensing receptor)
  2. causes activation of a signalling pathway and generation of arachidonic acid (AA)
  3. AA inhibits secretion of PTH
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9
Q

what switches off the signalling pathway to allow PTH secretion

A

reduced calcium levels switch off the signalling pathway to allow PTH secretion

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10
Q

is PTHR1(parathyroid hormone receptor 1) a GPCR

A

yes

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11
Q

what are the two main targets of PTH

A

bone and kidney cells

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12
Q

effects of PTH on calcium and phosphate in BONE

A

stimulates calcium and phosphate reabsorption by (indirectly) stimulating osteoclast activity

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13
Q

effects of PTH on calcium and phosphate on KIDNEY

A

enhances reabsorption calcium but decreases reabsorption of phosphate

ie increases phosphate excretion

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14
Q

effects of PTH on calcium and phosphate on INCREASED ABSORPTION

A

this effect in indirect and via synthesis of 1,25-dihydroxyvitamin D

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15
Q

what is bone

A

connective tissue containing several cell types surrounded by a protein matrix (osteoid)

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16
Q

what does a bone mainly contain

A

collagen

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17
Q

what is the organic matrix in the bone mineralised by

A

hydroxyapatite, a calcium-phosphate-hydroxide salt

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18
Q

is bone highly dynamic

A

yes

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19
Q

what are the key cells in regulating bone resorption and formation

A

osteoclasts and osteoblasts

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20
Q

what do osteoblasts do

A

mediate bone formation

secrete collagen and other proteins such as osteocalcin and osteopontin (collectively called osteoid)

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21
Q

what is the process of new bone matrix formation called

A

mineralisation, calcium and phosphate are associated with it

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22
Q

can osteoblasts become osteocytes

A

yes if they are embedded in the bone matrix

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23
Q

can osteoblasts be removed

A

yes by apoptosis or they can become inactive bone-lining cells

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24
Q

what do osteoclasts do

A

mediate bone resorption

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25
what do osteoclasts secrete
proteases and H+ ions
26
what do H+ ions do in the bone
dissolve the hydroxyapatite crystals and expose the organic matrix, allowing degeneration of collagen by proteases results in release of calcium and phosphate
27
does PTH act directly on osteoclasts
no, as osteoclasts lack a PTH receptor protein instead it binds to osteoblasts which leads to osteoclastogenesis from osteoclast precursor cell
28
how does PTH achieve osteoclastgenesis
by enhancing expression of RANK ligand (RANKL) and inhibiting expression of osteoprotegerin, a decoy receptor for RANKL
29
what does interaction of RANK with RANKL mediate
interaction of osteoblasts with osteoclast precursors
30
what blocks RANK-RANKL interaction
osteoprotegerin which binds to RANKL
31
does PTH stimulate the production of new osteoclasts
yes
32
steps of PTH stimulating production of new osteoclasts
1. PTH binds to osteoblast cells, causes increase in RANKL and decrease in osteoprotegerin 2. this enhances interaction of osteoblasts with osteoclast precursor cells 3. this leads to activation of signalling pathways that promote differentiation of the precursor cells into mature osteoclasts (which mediate bone resorption)
33
what does a decrease in osteoprotegerin lead to
more free RANK ligand which can now bind to rank as an osteoblast precursor
34
does PTH cause reabsorption of calcium in the kidneys
yes, reabsorption increases due to PTH stimulation of calcium transporter expression and activity
35
does PTH cause increased reabsorption of phosphate in the kidney
yes due to PTH stimulated internalisation and lysosomal degradation of a phosphate transporter ie removal from the plasma membrane
36
what is enhanced excretion of phosphate important form in kidneys
to prevent plasma levels of this ion rising as a result of increased resorption form bone and increased absorption from intestine
37
does PTH increase synthesis of 1,25-dihydroxyvitamin D
yes, which increases calcium and phosphate absorption from the intestines
38
is 1,25-dihydroxyvitamin D a steroid hormone
yes, it comes from cholesterol
39
does 1,25-dihydroxyvitamin D have a key role in regulating calcium and phosphate
yes
40
how is vitamin D synthesised
- in the body (requires sun exposure; UV light) - obtained from ingested food
41
is 1,25-dihydroxyvitamin D the active form of vitamin D
yes
42
does PTH increase synthesis of 1,25-dihydroxyvitamin D
yes
43
how does PTH increase synthesis of 1,25-dihydroxyvitamin D
by regulating expression of 25-hydroxyvitamin D 1-alpha-hydroxylase in the kidney
44
where does 1,25-dihydroxyvitamin D have its main effect
in the intestine
45
is 1,25-dihydroxyvitamin D a steroid hormone
yes, its receptor in inside the cell
46
what does 1,25-dihydroxyvitamin D binding to its receptor cause
gene expression changes
47
effect of 1,25-dihydroxyvitamin D on intestine
- increase calcium and phosphate absorption - effects are increased by increased expressions of calcium and phosphate transport proteins
48
effects of 1,25-dihydroxyvitamin D on kidneys
increases calcium reabsorption by increasing expression of transporter protein
49
what does 1,25-dihydroxyvitamin D protect bone from
the action of PTH by increasing calcium uptake from GI and therefore reducing PTH secretion
50
steps of 1,25-dihydroxyvitamin D regulation of calcium absorption
1. it enters cells 2. activates receptor in the nucleus 3. increased transcription/expression of calcium transport proteins 4. leads to increased absorption of calcium
51
overall effects of PTH and 1,25-dihydroxyvitamin D on calcium
- increased renal calcium resorption - increased bone resorption - increased ECF calcium - increased renal hydroxylation of 25-hydroxy-vitamin D
52
good sources of vitamin D
- from April to September we get it from sunlight - foods such as oily fish, red meet - dietary supplements
53
how much vit D do babies need
up to 1 year old need 8.5 to 10mcg a day
54
how much vit D do children and adults need
10mcg a day -- including pregnant and breastfeeding women
55
should formula fed babies get vitamin D supplements
no until they are having less than 500ml of formula per day
56
what does too much vitamin D cause
hypercalcaemia which can weaken bones and damage kidneys and heart
57
can you overdose on vit D through exposure to sunlight
no
58
does calcitonin (CT) lower blood calcium and phosphate levels
yes
59
is calcitonin a peptide hormone
yes
60
what secretes calcitonin
C-cells of the thyroid gland
61
when is calcitonin secreted
in response to an elevation in plasma calcium levels
62
is the CT receptor a GPCR
yes
63
two main sites of action for CT
osteoclasts in bone and kidney cells
64
does calcitonin inhibit resorption and promotes deposition
yes
65
how does calcitonin inhibit resorption and promote deposition
it inhibits the activity and differentiation of osteoclasts thus inhibits resorption and promotes deposition
66
does calcitonin play a large role in normal regulation of calcium and phosphate balance
no but may play a role in protecting skeletal integrity when there is a high calcium demand (such as pregnancy or breast feeding)
67
what controls PTH and calcitonin secretion
negative feedback - increase in plasma Ca = increase in calcitonin = decrease in plasma Ca - decrease in plasma Ca = increase in PTH = increase in vit D and plasma Ca

function of CNS and endocrine (29 decks)

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