parathyroid Flashcards
characteristics of parathyroid glands
-Shape-oval, bean, or teardrop appearance or flat shape when juxtaposed to thyroid gland.
-Color-yellowish brown to reddish brown in normal parathyroid glands and lighter gray tone in pathological states.
-4
serum PTH
-Tightly regulated by a negative feedback loop
-Primary function of PTH- To maintain the ECF calcium concentration
-PTH acts:
-Directly on bone and kidney
-Indirectly on intestine through its effects on synthesis of 1,25(OH)2D
-Final effect is — to increase serum calcium concentrations
-PTH production - regulated by the concentration of serum ionized calcium
calcium
-99% of body Ca is in bone
-1. 1% of bone Ca - freely exchangeable with the ECF -> Available for buffering changes in Ca balance
-2. About 40% of the total blood Ca -> Bound to plasma proteins, primarily albumin
-3. Remaining 60% includes -> Ionized Ca plus Ca complexed with phosphate (PO4) and citrate
-Maintenance of the body Ca2+ stores depends on (d/o)
-Dietary Ca2+ intake
-Absorption of Ca2+ from the GI tract
-Renal Ca2+ excretion
-1500 mg of Ca2+ ingested each day in a balanced diet
-About 200 mg/day is lost in bile and GI secretions
-Depending on the concentration of circulating vitamin D:
-200 to 400 mg of Ca is absorbed from the intestine each day
-The remaining 800 to 1000 mg appears in the stool
functions of calcium
-Skeletal muscle contraction
-Excitation-contraction coupling in cardiac and smooth muscle
-Activation of protein kinases and enzyme phosphorylation
-Ca helps regulate many enzymes -> Intracellular messengers, such as cAMP
-Nerve conduction
-Hormone release
-Blood coagulation
regulation of Ca metabolism
-Metabolism of Ca and of PO4 are intimately related
-Their balance is greatly influenced by circulating levels -> PTH, vitamin D, and, to a lesser extent calcitonin
-PTH and vitamin D important regulators of bone growth and bone remodeling
-Ca and inorganic PO4 corncentrations - also linked by their ability to chemically react to form CaPO4
-*CaPO4 is estimated to be 60 mEq/L
-If the product exceeds 70:
-Precipitation of CaPO4 crystals in soft tissue is likely
-Precipitation in vascular tissue accelerates arteriosclerotic vascular disease
regulation of Ca2+ by vitamin D
-PTH stimulates conversion of vitamin D → active form, 1,25(OH)2D
-This ↑ dietary Ca absorbed by the intestine
-Despite increased Ca absorption:
-Long-term increases in PTH secretion generally result in further bone resorption:
-by inhibiting osteoblastic function
-& promoting osteoclastic activity
calcium, sodium, and phosphate
-Renal Ca excretion generally parallels Na excretion
-Is influenced by many of the same factors that govern Na transport in the proximal tubule
-*But PTH enhances distal tubular Ca reabsorption independently of Na
-PTH also decreases renal PO4 reabsorption
-Therefore → increases renal PO4 losses
-This prevents the Ca-PO product from being exceeded as Ca levels rise in response to PTH
-i.e. – there is a decrease in serum [PO4] with an increase in [Ca] in response to PTH secretion
hypoparathyroidism
-Characterized by:
-Hypocalcemia
-Hyperphosphatemia
-Often produces chronic tetany
-Deficient PTH
-Commonly s/p thyroidectomy
-Accidental removal of or damage to several parathyroid glands:
-Transient hypoparathyroidism common after subtotal thyroidectomy
-Permanent hypoparathyroidism occurs after < 3% of thyroidectomies
-Autoimmune
-Infiltrative diseases (Wilson, hemochromatosis, granulomas, metastases)
types of hypoparathyroidism
-idiopathic hypoparathyroidism - Uncommon sporadic or inherited condition
-*DiGeorge syndrome- Congenital facial and cardiac anomalies -> Thymic aplasia abnormalities of the arteries arising from the brachial arches
-Hypomagnesemia- Causes functional hypoparathyroidism
-Severe hypomagnesemia – can cause suppression of parathyroid hormone (PTH) release and/or resistance
-Acute pancreatitis
hypoparathyroidism
-Manifestations of hypocalcemia
-Usually begin about 24 to 48 hrs postop
-May occur after months or years
-PTH deficiency
-More common after radical thyroidectomy for carcinoma
-Subtotal or total parathyroidectomy
-Risk factors for severe hypocalcemia after subtotal parathyroidectomy
-Severe preoperative hypercalcemia
-Removal of a large adenoma
-Elevated alkaline phosphatase
-Renalmanifestations of chronic hypoparathyroidism occur due to hypercalciuria* and include nephrolithiasis, nephrocalcinosis, and kidney disease.
hypocalcemia
-Commonest cause of low Ca- hypoalbuminemia
-Hypoparathyroidism
-Vitamin D deficiency
-Magnesium depletion
-Advanced renal disease (CKD)
hypocalcemia: symptoms
-ACUTE
-Tetany
-Carpopedal spasm
-Cramping
-Convulsions
-Circumoral and distal extremity tingling
-Irritability
-CHRONIC
-Lethargy
-Anxiety
-Parkinsonism
-Mental retardation
-Personality changes
-Blurred vision
signs of hypocalcemia
-Dry skin, brittle nails, or coarse hair ! (diff dx hypothyroidism)
-Heart failure, cardiac arrhythmias
-ECG with prolonged QT or ST flattening
-Cataracts with chronic hypocalcemia
-Laryngospasm
-Papilledema
-Encephalopathy or dementia with severe hypocalcemia
-Seizures (rare)
-Spontaneous or latent tetany
-Chvostek’s sign
-Percussion of the ipsilateral facial muscle anterior to the ear causes facial muscle contraction
-Commonly seen in eucalcemic individuals (5%)
-Worthwhile to check this in patients before parathyroid surgery
-Trousseau’s sign
-Carpal spasm after 3min of occlusion with a blood pressure cuff
-Rarely used in clinical practice
pseudohypoparathyroidism
-Uncommon group of disorders
-Characterized by target organ resistance! to PTH
-Complex genetic transmission of these disorders
-Albright’s hereditary osteodystrophy
-Hypocalcemic, as a result of hyperphosphatemia
-2ry hyperparathyroidism and hyperparathyroid bone disease
-Short stature, round facies, mental retardation with calcification of the basal ganglia, shortened metacarpal and metatarsal bones, mild hypothyroidism, and other subtle endocrine abnormalities
vitamin D deficiency
-Inadequate dietary intake
-Decreased absorption due to
-Hepatobiliary disease
-Intestinal malabsorption
-Drugs that alter metabolism of Vit. D (phenobarbital, phenytoin, rifampin)
-Lack of skin exposure to sunlight
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