高钙血症

Calcitonin
Secreted by Parafollicular (C cells) in the thyroid
Temporarily lowers calcium levels
Decreases osteoclastic activity
Stimulated by high calcium lewk.baidu.comels
Fatigue Depression Constipation Anorexia Polyuria
Most common nocturia
Parathyroid poisoning
Calcium > 17mg/dl
Calcium phosphate crystals precipitate
Findings with Hypercalcemia
Bony tenderness Hyperactive tendon reflexes Tongue fasciculations Hypercalcemia in pregnancy
May cause hypocalcemia in the neonate
Parathyroid and Bone
PTH stimulates osteocytic pump
Increases permeability of osteocytic membrane allowing calcium to diffuse
Osteoblasts,cytes and clasts do not have PTH receptors
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
Band Keratopathy
Deposition of Calcium
Corneal opacities Long standing hypercalcemia Associated with primary
hyperparathyroidism Calcium deposition begins near
Stimulating a distal tubular - mediated calciuresis
Calcium Caveats
Respiratory alkalosis and elevated pH
Increase in the binding of calcium Lowers ionized calcium.
Suppressing the fetal parathyroid
Hypercalcemia
Small decrease in GFR
Hemodynamic effects & hyposthenuria (a loss of renal concentrating abilities)
Findings with Hypercalcemia
Complications of Hypercalcemia
Sinus bradycardia Increase in the degree of a heart block Cardiac arrhythmia Hypertension Pancreatitis Peptic ulcer disease Nephrolithiasis Accelerated vascular calcification
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
Decrease in pH has the opposite effect.
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.
? function
Responsible for calcium homeostasis
Kidney Bone
Parathyroid Actions
Increases calcium
Regulates intestinal absorption
25-OH vitamin D 1,25-OH vitamin D
Renal absorption of calcium/excretion of phosphorus
Bone reabsorption
Osteolysis
Parathyroid and Bone
Osteoblasts + Osteocytes = Osteocytic membrane system
PTH stimulates osteoblasts and cytes, which then activate osteoclasts via “signaling” system
PTH indirectly stimulates formation of new osteoclasts
Both cell lines are activated but clastic activity > blastic
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
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 -
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
CALCIUM
REGULATION _
PTH
+
_ 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
excreted into bile and other intestinal secretions. So only 20% of the total amount of Ca ingested daily is available to circulate between bone and extracellular fluid.
Hypercalcemia
Heidi Chamberlain Shea, MD Endocrine Associates of Dallas
Goals of Discussion
Review Calcium metabolism Differential Diagnosis of Hypercalcemia Treatment options Calcium case presentations
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
Osteocytic pumps
Pump calcium from bone to ECF To maintain calcium concentration in bone
fluid, osteolysis occurs and calcium phosphate is resorbed from bone Fibrous and gel matrix remain intact
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%
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
millimeters Often accidentally
removed Normal function with
at least 2 glands
Parathyroid
Composed
Chief cells
Synthesize, secrete and store PTH
Oxyphil cells