Citrate and phosphate Not ionized Diffusible
50% is diffusible and ionized
Most important in bodily functions
Effects of Calcium Hypocalcemia
Increased neuronal membrane permeability to sodium ions facilitates action potentials
Calcitonin
Secreted by Parafollicular (C cells) in the thyroid
Temporarily lowers calcium levels
Decreases osteoclastic activity
Stimulated by high calcium levels
CALCIUM
REGULATION _
PTH+_源自1,25(OH)2 D3+
+
+
+
CALCITONIN
_
GI Tract
ECF Pool of Calcium
BONE
URINE
Parathyroid
Four glands located behind the thyroid
Length 6 millimeters Width 3 millimeters Thickness 2
Calcium
41% combined with plasma proteins
Not diffusible One gram per deciliter of albumin binds
approximately 0.8 mg/dl of calcium
9% combined with anionic substances
Findings with Hypercalcemia
Bony tenderness Hyperactive tendon reflexes Tongue fasciculations Hypercalcemia in pregnancy
May cause hypocalcemia in the neonate
Calcium Homeostasis
Hormones
PTH Vitamin D Calcitonin
Organs
Bone Kidney Small intestine
1,25-OH Vitamin D
Calcium Physiology Target Organs
Small intestine : approx. 40% absorbed, 50% of that -
Renal absorption of calcium/excretion of phosphorus
Bone reabsorption
Osteolysis
Parathyroid and Bone
Osteoblasts + Osteocytes = Osteocytic membrane system
Stimulating a distal tubular - mediated calciuresis
Calcium Caveats
Respiratory alkalosis and elevated pH
Increase in the binding of calcium Lowers ionized calcium.
When calcium levels < 6mg/dl
Tetany Chvostek’s sign Trousseau’s sign
Calcium <4mg/dl = Death
Effects of Hypercalcemia
Calcium >12 mg/dl
Nervous system depressed
Fatigue Depression Constipation Anorexia Polyuria
Most common nocturia
Parathyroid poisoning
Calcium > 17mg/dl
Calcium phosphate crystals precipitate
reabsorbed Distal nephron - about 10% reabsorbed. PTH and activated Vit D
increases Ca absorption during Ca deficient states.
Normally kidney excretes approx. 200 mg /day of Ca to maintain homeostasis. During states of severe Ca depletion, the Kidney can decrease urinary excretion to 50mg /day or less.
Hypercalcemia
Heidi Chamberlain Shea, MD Endocrine Associates of Dallas
Goals of Discussion
Review Calcium metabolism Differential Diagnosis of Hypercalcemia Treatment options Calcium case presentations
Suppressing the fetal parathyroid
Hypercalcemia
Small decrease in GFR
Hemodynamic effects & hyposthenuria (a loss of renal concentrating abilities)
Findings with Hypercalcemia
Role of Calcium
Bone mineralization Muscle contraction
Skeletal Cardiac Smooth muscle
Blood clotting Nerve impulse transmission
Bone metabolism Parathyroid hormone (PTH) Calcium Phosphorus Vitamin D Calcitonin
the limbus at the 3 & 9 o’clock position Less friction from the lids near the limbus Tear film is most alkaline in the most exposed area, band running across the cornea from the 3 to 9 o’clock position
millimeters Often accidentally
removed Normal function with
at least 2 glands
Parathyroid
Composed
Chief cells
Synthesize, secrete and store PTH
Oxyphil cells
Kidney :
Glomerulus filters out the Ca that is not bound to protein. Proximal tubule - approx. 50% to 70% is reabsorbed, Ca
reabsorption mirrors Na reabsorption. Ascending limb of the loop of henle - approx. 30% to 40%
Decrease in pH has the opposite effect.
Band Keratopathy
Deposition of Calcium
Corneal opacities Long standing hypercalcemia Associated with primary
hyperparathyroidism Calcium deposition begins near
Calcium Physiology
An essential intracellular and extracellular cation Extracellular calcium is required to maintain
normal biological function of nervous system, the musculoskeletal system, and blood coagulation Intracellular calcium is needed for normal activity of many enzymes Preservation of the integrity of cellular membrane Regulation of endocrine and exocrine secretory activities Activation of compliment system Bone metabolism
? function
Responsible for calcium homeostasis
Kidney Bone
Parathyroid Actions
Increases calcium
Regulates intestinal absorption
25-OH vitamin D 1,25-OH vitamin D