Endocrine Lecture 5: Calcium and Parathyroid Flashcards
What functions in the body does Calcium contribute to?
- Nerve conduction
- Bone formation
- Muscle function
- Blood coagulation (factor IV is Ca ion)
- Cerebral and cardiac function Capillary permeability
- Cell growth and division
- Neurotransmitter action
Where and in what ways is Ca stored or present in the body?
Body contains 1-2 kg of calcium
- 98% in skeleton
- 1% in cells
- 0.1% in ECF
- 0.03% in plasma
Plasma Ca is present in the following forms in the body:
-50% Ionized (active form)
Most important form for calcium functions on heart, the nervous system, and bone formation
-41% protein bound (primarily albumin)
-9% combined with anions (diffusible)
Equilibrates with bone Ca++, but only 0.5% of bone calcium is readily exchangeable
Rest is slowly exchangeable
How does HYPOcalcemia manifest?
Nervous system excitement
• Increased neuronal permeability to Na, easy action potentials • 50% ion/ 35% total decrease leads to spontaneous discharges • Tetany, seizures
– Most common in hand: carpopedal spasm
-Or face:Chvosteks sign:tapping facial nerve leads to twitching
• Longer QT
How does HYPERcalemia manifest?
Chief manifestation is skeletal muscle weakness
– Nervous system depression
• Short QT, long PR interval, constipation, anorexia
– Treatment:
• Maintain UOP, hydrate, administer mithramycin in severe cases
Where and in what ways is Phosphorus stored or present in the body?
Body contains 1 kg of phosphorus
• 85% skeletal, 15% muscle/tissue, 1% ECF
– Circulates in plasma 12% protein bound
– Levels fluctuate significantly more than Ca++ because Ph moves between ECF and bone as well as between ECF and ICF
Where is the major control site of Phosphorus balance?
Major control site is kidney:
– Urinary excretion balances GI intake
– PTH increases urinary excretion
• Calcitonin to a lesser extent
– GI absorption increased by 1,25 D3The Parathyroid consists of __ glands located behind the upper and lower poles of the ___ gland.
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Thyroid
The Parathyroid glands are very small, they contain mainly ___ cells and ___ cells.
Chief and oxyphil cells
Chief cells secrete _____.
Parathyroid Hormone
Synthesis and secretion of parathyroid hormone is related to _____ concentrations in the blood.
Calcium
These 3 conditions can cause enlargement of the parathyroid gland:
Prolonged stimulation
Pregnancy
Lactation
Decreases in ECF concentration of ____ increases the secretion of Parathyroid Hormone (PTH)
Calcium
Likewise:
Increases in calcium concentration in the extracellular fluid decreases the activity of the parathyroid gland
Vitamin D (Cholecalciferol) and Calcitonin both help with reabsorption of Ca from the ______ of the kidney?
Proximal tubules
What are the main actions of PTH?
- Major stimulus is low serum Ca++ level
- Increases bone resorption to mobilize calcium and phosphate
-Increases reabsorption of Ca++ in the kidney’s distal tubules
• Decreases reabsorption of phosphate in the renal tubules
• Increases the production of 1,25-dihydroxycholecalciferol
Increased release of PTH results in:
-Increases the excretion of phosphate, potassium, and sodium by increasing the calcium/magnesium/hydrogen reabsorption
(largely in the distal tubules and collecting ducts)
Serum: Increased calcium, decreased phosphate
Urine: Decreased calcium, increased phosphate
Where is Calcitonin produced?
parafollicular (clear or C cells) of the thyroid
What are the main effects of Calcitonin?
-In general it has the opposite effect of parathyroid hormone
Secretion is controlled by serum calcium level
• Increased Ca++ leads to in creased secretion
Serum:
– Decreased calcium
– Decreased phosphate
Urine:
– Increased calcium excretion
– Increased phosphate excretion
What is the active form of Vitamin D and how/where is it converted to it’s active form?
Vitamin D is not itself an active substance, but must be converted to its active product 1,25-dihydroxycholecalciferol
Vitamin D3 is converted to 1,25-dihydroxycholecalciferol by the liver
What are the main functions of vitamin D (D3/1,25-dihydroxycholecalciferol)?
Vitamin D has a potent effect to increase calcium absorption from the intestinal tract
Vitamin D has important effects on both bone deposition and bone absorption
GI absorption of Ca++ is increased by Vitamin D
Calcium regulation:
Urinary excretion of Ca is decreased by ____ and increased by ____.
decreased by PTH (parathyroid hormone)
increased by calcitonin
Calcium regulation:
Bone respiration is increased by _____ and inhibited by _____.
Increased by PTH
inhibited by Calcitonin
What is the primary cause of HYPOparathyroidism?
Usually a result of surgical damage to the gland during thyroid surgery
Calcium levels fall below normal in 24-72
surgical damage to the parathyroid gland during thyroid surgery causes Calcium levels to fall below normal in 24-72 hours which results in:
- Tetany: calcium ion interferes with membrane transport and interferes with the relaxation of the muscle
- Muscle cramps
- Grand mal seizures
- Cardiovascular collapse
Treatment for Hypocalcemia related to impaired PTH production:
PTH – expensive, short half life High calcium and Vit D intake
Occasionally 1/25-D3 necessary
- Hypomagnesemia can cause hypocalcemia resistant to calcium
- Must treat first with magnesium
- Magnesium suppresses the release of PTH
What is Primary Hyperparathyroidism?
Primary: inappropriate hypersecretion of PTH resulting in hypercalcemia
Results in hypercalcemia, hypercalciuria, hypophosphatemia, hyperphosphaturia, bone demineralization
Effects cardiac function (shortens QT interval, depresses relaxatioin)
Causes Kidney stone formation as Ca++ mobilized from bone must eventually be excreted by kidneys
Most common cause of hyperparathyroidism is parathyroid hyperplasia or parathyroid tumor
Pregnancy may stimulate the parathyroids
What is Secondary Hyperparathyroidism?
Hyper secretion of PTH in response to a hypocalcemic stress examples: Vitamin D deficiency and Chronic renal disease
• Results in osteomalacia
– Inadequate mineralization of the bones
Vitamin D deficiency in children manifests as:
Rickets – bones fail to mineralize, epiphyses fail to fuse, epiphyseal plates widen and bowing and fractures occur

Vitamin D deficiency in adults manifests as:
osteomalacia- inadequate mineralization of the bones
Sources of Vitamin D deficiency:
Inadequate dietary intake
Often due to fat malabsorption syndrome
Inadequate sunlight
Decreased absorption of calcium and phosphate, decreased serum calcium and phosphate, increased PTH and increased bone resorption
One gram of Calcium Chloride contains the equivalent amount of ionized calcium as __ grams of Calcium Gluconate
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_____ is indicated for treatment of hyperkalemia induced EKG changes because of its cell membrane stabilizing effects.
Calcium
Calcium is indicated for treatment in patients with hypotension associated with either ____ ____ ___ or beta adrengergic blockers.
Calcium Channel Blockers
The treatment for Magnesium toxicity associated with treatment of preeclampsia is:
Calcium
Calcium is contraindicated in patients with ____ toxicity as it may cause lethal arrhythmias.
Digoxin
Digibind is an immunoglobulin fragment that binds with digoxin. It is currently considered first-line treatment for significant dysrhythmias (eg, severe bradyarrhythmia, second- or third-degree heart block, ventricular tachycardia or fibrillation) from digitalis toxicity.
