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1. Calcium regulation
(c) Natalia Dachanidze

2. PARATHYROID HORMONE
•PTHisapeptidehormonewhichissynthesised
intheparathyroidglands.
•Itsmainfunctionistoincreasethe
concentrationofcalciuminthebloodplasma.
•IntactPTH(iPTH)isthebiologicallyactiveform
andissecretedwhenthecalciumlevelislow.
(c) Natalia Dachanidze

3. (c) Natalia Dachanidze

4. CALCITONIN
•Calcitonin(alsoknownasthyrocalcitonin)is
producedinthethyroidglandandisthe
antagonistofPTH.
•Theproductionandsecretionofcalcitoninis
stimulatedbyanelevatedcalciumleveland
resultsinareductioninthecalcium
concentrationintheblood.
(c) Natalia Dachanidze

5. (c) Natalia Dachanidze

6. VITAMIN D
•VitaminDexistsintwoforms:vitaminD2
whichisacquiredbyconsumptionofplantfoods
suchasmushroomsandavocado,andvitamin
D3whichisobtainedfromanimalfoodsources
orproducedinskinexposedtoultravioletB
radiation.
(c) Natalia Dachanidze

7. (c) Natalia Dachanidze

8. (c) Natalia Dachanidze

9. Introduction
•Total plasma [Ca++] = 2.5mmol/L
•Range is 2.0 to 2.5 mmol/L
•Very tightly controlled
Body
content
Bone intracellu
lar
extracellu
lar
Calcium 1300gms 99% 1% 0.1%
(c) Natalia Dachanidze

10. Introduction
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11. Factors affecting calcium concentration
1) Changes in plasma protein concentration
-Increased [protein] –increased total [Ca2+]
2) Changes in anion concentration
-Increased [anion] –increased fraction of Ca2+
that is complexed–decrease ionized [Ca2+]
3)Acid-base abnormality (pH)
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12. Acid Base Abnormality
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13. Functions of Calcium
•1.Nerveandmusclefunctions
•Depolarizationandmusclecontaction
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14. •Increase in intracellular Ca
2+
concentration →
Ca
2+
binds to troponin C →conformational
change in the troponin complex →moves
tropomyosinout of the way →permitting the
binding of actin to the myosin heads leading
cross-bridge formation and the muscle contracts
as a whole
(c) Natalia Dachanidze

15. Functions of Calcium
Cross bridge
cycling
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16. Functions of Calcium
•2. Homeostasis
-activation of clotting enzyme is the plasma
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17. Functions of Calcium
•3.Preservingbonedensity
-construction,formationandmaintenanceof
boneandteeth.Thisfunctionhelpsreducethe
occurrenceofosteoporosis
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18. Functions of Calcium
•4.Neurotransmitterrelease
-Directlyproportionaltothecalciumlevel
-Arrivalofactionpotentialtoaxonalterminal
→openingofvoltagegatedcalciumchannels
→calciuminfluxintotheterminal→transmitter
vesiclefusewiththereleasesites→exocytosis-
releaseoftransmittersintothecleft
(c) Natalia Dachanidze

19. Functions of Calcium
•5.Calciumassistsinmaintainingallcellsand
connectivetissuesinthebodyandregulating
mitotictransitionandcelldivision.
•6.Essentialcomponentintheproductionof
enzymeandhormonesthatregulatedigestion,
energy,andfatmetabolism.
(c) Natalia Dachanidze

20. Calcium Homeostasis
•Blood calcium is tightly regulated by:
1) Principle organ systems:
Intestine
Bone
Kidney
2) Hormones:
Parathyroid hormone (PTH)
Vitamin D
Calcitonin
(c) Natalia Dachanidze

21. Calcium Homeostasis
(c) Natalia Dachanidze

22. Parathyroid Hormone (PTH)
•Thereare4parathyroidsglands,locatedonthe
dorsalsideofthethyroid
•Thebloodsupplytotheparathyroidglandsis
fromthethyroidarteries.
(c) Natalia Dachanidze

23. Parathyroid Hormone (PTH)
• Chief cells secrete PTH
• Oxyphilcells –function unknown. Probably
degenerated chief cells
(c) Natalia Dachanidze

24. Parathyroid Hormone (PTH)
•Mechanism
Increaseinextracellularcalciumconcentration
→Ca
2+
bindstothereceptorandactivates
phospholipaseC→increasedlevelsofIP
3/Ca
2+
→whichinhibitsPTHsecretion.
WhenextracellularCa
2+
isdecreased,thereis
decreasedCa
2+
bindingtothereceptor,which
stimulatesPTHsecretion.
(c) Natalia Dachanidze

25. Parathyroid Hormone (PTH)
•Actions of PTH on bone, kidney and small
intestine
1)Actions on bone
-Overall effect : promote bone resorption and
increase calcium concentration
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26. Parathyroid Hormone (PTH)
•2. Actions on kidneys
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27. Parathyroid Hormone (PTH)
a)Inhibits PO4 reabsorption (inhibits Na-PO4
cotransport in PCT) –phosphaturia –less
complexed Ca-PO4 –increase plasma calcium
b)Stimulates calcium reabsorption
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28. Parathyroid Hormone (PTH)
•3.Actionsonsmallintestine(indirect)
-StimulatesCa2+reabsorptionviaactivationof
vitaminD.
(c) Natalia Dachanidze

29. Parathyroid Hormone (PTH)
(c) Natalia Dachanidze

30. Vitamin D
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31. Vitamin D
•Actions of vitamin D
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32. Calcitonin
•astraight-chainpeptidewith32aminoacids.
•synthesizedandsecretedbytheparafollicular
cellsofthethyroidgland.
•majorstimulusforcalcitoninsecretionis
increasedplasmaCa
2+
concentration
•Themajoractionofcalcitoninistoinhibit
osteoclasticboneresorption,whichdecreases
theplasmaCa
2+
concentration.
(c) Natalia Dachanidze