1 / 27

Got Calcium?

Got Calcium?. Ca 2+. Plasma Calcium Regulation. Plasma calcium totals 2.4 mM (9.4 mg/dl) Free calcium is 1.2 mM. Plasma Calcium Regulation. Free calcium is tightly regulated ( 5%) Too low = neuronal hyper-excitability Too high = neuronal depression Control points for calcium

jaden
Download Presentation

Got Calcium?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Got Calcium? Ca2+

  2. Plasma Calcium Regulation • Plasma calcium totals 2.4 mM (9.4 mg/dl) • Free calcium is 1.2 mM

  3. Plasma Calcium Regulation • Free calcium is tightly regulated (5%) • Too low = neuronal hyper-excitability • Too high = neuronal depression • Control points for calcium • Absorption – Via intestines • Excretion – Via urine • Temporary storage – Via bones

  4. Active Control of Calcium • Vitamin D3 • Diet and sun • Parathyroid hormone • Parathyroid gland • Calcitonin • Thyroid gland • Skeletal loading • Osteoblasts and osteoclasts

  5. Vitamin D3 and Calcium Control • Vitamin D3 (Cholecalciferol) • Converted to precursor in liver • Initially stored • Converted to 25-Hydroxycholecalciferol • Feedback control limits concentration • Converted to active form in kidney • 1,25-Dihydroxycholecalciferol • Under the feedback control of parathyroid hormone (PTH)

  6. Effects of Active Form of Vit D3 • Promotes intestinal absorption of calcium • Causes synthesis of calcium-binding protein and related facilitated transport • Takes a couple of days to fully develop response • Has slight effect to increase calcium re-absorption in kidneys • Works with PTH to cause calcium absorption from bone

  7. Parathyroid Hormone • Secreted by parathyroid glands • Rapid response to reduced calcium (minutes) • Polypeptide • 84 amino acid residues • 9,500 daltons M.W. • Peptide fragments can be active for periods measured in hours • Operates in tissues via cAMP second messenger

  8. Parathyroid Hormone

  9. Calcium Signal Transduction in Parathyroid Gland • G-Protein Coupled Receptor • Activates Phospholipase C • Leads to increased Diacylglycerol (DG) and Inositol trisphosphate (IP3) as secondary messengers • Inhibits adenylate cyclase to reduce cAMP • Present in C cells of Thyroid Gland • Regulates calcitonin secretion 600 AA external domain Phosphorylation sites 200 AA internal domain

  10. Effects of PTH • Increases calcium absorption from bone • Existing osteocytes stimulated (minutes to hours) to transport calcium – calcium pumps • Existing osteoclasts activated and new osteoclasts formed (days to weeks) to digest bone and release calcium • Stimulated indirectly by osteoblasts

  11. Other Effects of PTH • Decreases excretion of calcium by kidneys • Important to prevent bone deterioration • Increases calcium absorption • Effect manifested via Vitamin D3 • Produces most active form of D3 in the kidney (1,25-dihydroxy-cholecalciferol)

  12. Hyperparathyroidism

  13. Calcitonin • Secreted by the thyroid gland • Effects are much less than those of PTH

  14. Effects of Calcitonin • Attenuates absorptive ability of osteoclasts • Inhibits formation of new osteoclasts • Osteoclast decrease causes osteoblast decrease • Effect to decrease calcium is transitory • Causes reduced bone turnover • Has weak effect in kidney and intestines

  15. Non-Hormonal Control of Plasma Calcium • Changes in calcium intake can be rapidly accommodated • Buffer capacity of amorphous calcium in bone • Calcium is sequestered in intracellular spaces • Can help restore plasma calcium in tens of minutes

More Related