2. Facts About Calcium
Date of Discovery: 1808
Discoverer: Sir Humphrey Davy
Name Origin: From the latin word calcis
(lime)
Uses: life forms for bones and shells
Obtained From: chalk, limestone, marble.
3.5% of crust
3. Physiological importance of Calcium
Calcium salts in bone provide structural integrity
of the skeleton
Calcium ions in extracellular and cellular fluids is
essential to normal function of a host of
biochemical processes
Neuoromuscular excitability
Blood coagulation
Hormonal secretion
Enzymatic regulation
4. Calcium Homeostasis
99% of body calcium is in the skeleton
0.9 % intracellular
0.1% extracellular
45% bound to plasma proteins mainly albumin
45% in ionized form (the physiologically active form)
10% complexed with anions (citrate, sulfate, phosphate)
Corrected calcium = (4-serum albumin) X 0.8 + measured serum
calcium
5. Calcium Regulation
Parathormone (PTH)
4 parathyroid glands
Release of PTH (chief cells) in response to drop in serum calcium
Magnesium needed to activate PTH release
Effects on bone, kidney and indirectly on intestines
Activates osteoclasts/osteoblasts leading to bone resorption and release
of calcium and phosphorous
Promotes reabsorption of calcium and excretion of phosphorous in the
kidney
Activates vitamin D
6.
7.
8. Calcium Regulation
Vitamin D
2 sources
Skin and Diet.
25 (OH) Vitamin D
Storage form of Vitamin D.
Liver.
1,25 (OH) Vitamin D
Active form of Vitamin D.
Activated by PTH and hypophosphatemia through 1-alpha
hydroxylase enzyme in the kidney.
9.
10. Calcium Regulation
PTH secretion responds to small alterations in plasma
Ca2+ within seconds.
A unique calcium receptor within the parathyroid chief
cell membrane senses changes in the extracellular fluid
concentration of Ca2+.
This is a typical G-protein coupled receptor that activates
phospholipase C and inhibits adenylate cyclase
increase in intracellular Ca2+ via generation of inositol
phosphates and decrease in cAMP which prevents
exocytosis of PTH from secretory granules.
12. Calcium Regulation
• When Ca2+ falls, cAMP rises and PTH is secreted.
• 1,25-(OH)2-D inhibits PTH gene expression, providing another
level of feedback control of PTH.
• Despite close connection between Ca2+ and PO4, no direct
control of PTH is exerted by phosphate levels.
13. Calcium Homeostasis
Calcitonin
Little role in calcium homeostasis.
Secreted by parafollicular C cells of thyroid.
Neural cell origin
Medullary Hyperplasia/Cancer
Most sporadic case
MEN IIA or IIB
15 % cases
14. Parathyroid “C” Cells
PTH Calcitonin
Bone
Kidney
Intestine
Bone
Kidney
[Ca++] [Ca++]
Stimulate
Stimulate
Inhibit
Inhibit
In plasma In plasma
Calcium Homeostasis
15. Maximum
secretion of PTH
occurs at plasma
Ca2+ below 3.5
mg/dL.
At Ca2+ above 5.5
mg/dL, PTH
secretion is
maximally
inhibited.
16. Hypercalcemia
Symptoms and Signs
Only 20 % people with hypercalcemia exhibit
signs and symptoms
“Calcium Stones, fragile bones, abdominal
groans, psychic moans and fatigue overtones”
17.
18. Etiologies of Hypercalcemia
Increased GI Absorption
Milk-alkali syndrome
Elevated calcitriol
Vitamin D excess
Excessive dietary intake
Granuomatous diseases
Elevated PTH
Hypophosphatemia
Increased Loss From Bone
Increased net bone resorption
Elevated PTH
Hyperparathyroidism
Malignancy
Osteolytic metastases
PTHrP secreting tumor
Increased bone turnover
Paget’s disease of bone
Hyperthyroidism
Decreased Bone Mineralization
Elevated PTH
Aluminum toxicity
Decreased Urinary Excretion
Thiazide diuretics
Elevated calcitriol
Elevated PTH
19. Familial Hypocalciuric
Hypercalcemia
(FHH)
Genetic, autosomal dominant
Mimics primary hyperparathyroidism
PTH slightly high, however inappropriate for
level of calcium
Mutation in parathyroid calcium sensor
Higher setpoint
Low urinary calcium/creatinine <0.01
No end organ damage
No treatment required
20. Etiologies of Hypocalcemia
Decreased GI Absorption
Poor dietary intake of calcium
Impaired absorption of calcium
Vitamin D deficiency
Poor dietary intake of vitamin D
Malabsorption syndromes
Decreased conversion of vit. D to calcitriol
Liver failure
Renal failure
Low PTH
Hyperphosphatemia
Decreased Bone Resorption/Increased
Mineralization
Low PTH (aka hypoparathyroidism)
PTH resistance (aka pseudohypoparathyroidism)
Vitamin D deficiency / low calcitriol
Hungry bones syndrome
Osteoblastic metastases
Increased Urinary Excretion
Low PTH
s/p thyroidectomy
s/p I131 treatment
Autoimmune hypoparathyroidism
PTH resistance
Vitamin D deficiency / low calcitriol
21. Hypocalcemia
PTH Resistance
Pseudohypoparathyroidism
Congenital defect
Absent metacarpal, short stature, round face, mental disability
Target organ unresponsiveness to PTH
Serum PTH levels high
&lt;number&gt;
Low ca causes the PT to release PTH. The osteoclasts of the bone release Ca and Ca is abosrbed from the kidney and Intestine. The increase of Ca in the blood