PSL201 – Mar 4 – Endocrine 5 Calcium Balance.docx

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11 Apr 2012
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PSL201 Mar 4 Endocrine 5: Calcium Balance
Calcium Balance
- triggers exocytosis of various substances
- stimulates muscle contraction
- increases the contractility of the heart andblood vessels
- hypercalcemia (increase in plasma calcium) causes muscle weakness and
atrophy, lethargy, behavioral changes, hypertension, constipation and nausea
- hypocalcemia (decrease in plasma calcium) causes numbness, muscle
cramps, spasms, exaggerated reflexes, and hypotension
- regulated through the interaction of the kidneys, digestive tract, bone, and
skin.
- Mostly located in bones, 99%
Renal Handling of Calcium Ions
- Ca+ is transported both in blood plasma and by carriers
o Plasma Ca+ is filtered by the glomerulus
99% is reabsorbed
Hormonal Control of Plasma Calcium Concentrations
- there are several hormones that regulate plasma calcium levels:
Effects of Parathyroid Hormone (PTH):
- peptide hormone produced in the parathyroid glands and secreted due to
low Ca+ levels
- stimulates calcium reabsorbtion in the assending loop of Henle and the DT,
which decreases the excretion of calcium and sustains plasma calcium levels
- stimulates the activation in kidneys of dihydroxycholecalciferol, which
stimulates calcium absorbtion in the digestive tract and kidneys
- stimulates resorption of bone, increasing plasma calcium levels
Effects of 1,25-Dihydroxycholecalciferol (1,25-(OH)2D3):
- steroid hormone that increases plasma calcium levels by stimulating calcium
absorbtion from the digestive tract and calcium reabsorbtion in the DT
- synthesized from vitamin D3
Effects of Calcitonin
- decreases plasma calcium levels
- secreted from C cells of the thyroid
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