Calcium and Parathyroids Flashcards by Kelsey Fuller

Why is calcium important?

Nerve conduction
Bone formation 
Muscle function
Blood coagulation
Cerebral and cardiac function
Capillary permeability
Cell growth and division
Neurotransmitter action

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How much calcium is contained in the body? and where is it located?

Body contains 1-2 kg of calcium

98% in skeleton***
0.03% in plasma
0.1% in ECF
1% in cells

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How does plasma calcium present?

50% Ionized (active form)***
41% protein bound (primarily albumin)
9% combined with anions (diffusible)

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Which form of calcium is the most important?

IONIZED

Most important form for calcium functions on heart, the nervous system, and bone formation

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What % of bone calcium is readily exchangable?

Equilibrates with bone Ca++, but only 0.5% of bone calcium is readily exchangeable

The rest is slowly exchangeable

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What does hypocalcemia cause?

Nervous system excitement

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How does the nervous system excitement occur with hypocalcemia?

Increased neuronal permeability to Na, easy action potentials

50% ion/ 35% total decrease leads to spontaneous discharges

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What happens with hypocalcemia?

Tetany, seizures
Most common in hand: carpopedal spasm
Or face: Chvosteks sign: tapping facial nerve leads to twitching

Longer QT (can develop R on T)

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How does hypercalcemia manifest?

muscle weakness

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Nervous system depression happens with hypercalcemia, how does this manifest?

Short QT, long PR interval, constipation, anorexia

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What is the treatment for hypercalcemia?

Maintain UOP, hydrate, administer mithramycin in severe cases

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How much phosphorous is in the body? and where is it located?

1kg

85 % skeletal
15% muscle/tissue
1% ECF

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Phospherous circulates in plasma 12% _____

protein bound

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Why do phos levels fluctuate more than Ca levels?

Levels fluctuate significantly more than ca++ because phos moves between ECF and bone as well as between ECF and ICF

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is the effects of phos minimal or maximal with large fluctuations?

minimal

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How does phos enter the ECF?

GI, ICF, bone

Easily absorbed in GI

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How does phos leave?

via urine, ICF, bone

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What is the major control site of phos?

Kidney

Urinary excretion balances GI intake
PTH increases urinary excretion
Calcitonin to a lesser extent
GI absorption increased by 1,25 D3

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How many glands does the parathyroid have?

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Where are they parathyroid glands located?

Located behind the upper and lower poles of the thyroid

very small in size

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What cells do the parathyroid glands contain?

They contain mainly chief cells and oxyphil cells

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*** What do chief cells secrete?

parathyroid hormone

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What is synthesis and secretion of the parathyroid hormone related to?

calcium concentrations in the blood

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What are parathyroid glands enlarged from?

Enlarged from prolonged stimulation, pregnancy, lactation

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What does a decrease in calcium concentration in the ECF cause?

increases the secretion of PTH

What does a increase in calcium concentration in the ECF cause?

decreases the activity of the parathyroid gland

What is another name for Vit D

Cholecalciferol

What does PTH, Vit D, and calcitonin help with?

All help with reabsorption of Ca from the proximal tubules of the kidney

*** PTH Actions: Increases bone resorption to mobilize ______

calcium and phosphate

*** What does bone resorption mean?

Bone resportion is the process by which osteoclasts break down bone and release calcium from bone fluid to blood

Is bone resorption fast or slow?

Rapid: activation of bone cells for rapid reabsorption Delayed: activates/proliferates osteoclasts for bone matrix breakdown

What does PTH do in regard to Ca and the kidney?

Increases reabsorption of Ca++ in the kidney’s distal tubules

What does PTH do in regard to Phos and the kidney?

Decreases reabsorption of phosphate in the renal tubules

*** What does PTH increase the production of?

Increases the production of 1,25-dihydroxycholecalciferol Vit D metabolite which enhances intestinal Ca++ absorption

*** What is a major stimulus for 1,25-dihydroxycholecalciferol?

low serum Ca++ level

Increases in PTH result in: Serum - Urine -

Serum: Increased calcium, decreased phosphate Urine: Decreased calcium, increased phosphate

Increased PTH results in increased excretion of _____, _____, _____ by reabsorbing mire _____, _____, _____

phosphate, potassium, and sodium calcium, magnesium, hydrogen (this happens largely in distal tubules and collecting ducts)

Where is calcitonin produced?

in the parafollicular (clear or C cells) of the thyroid

Calcitonin has the opposite effect of what?

parathyroid hormone

What does Calcitonin do to Ca levels? How?

decreases Ca levels Inhibits bone resorption Increases urinary excretion of calcium Immediate: decreases osteoclastic activity and osteolysis of osteocytes Delayed: Decreases osteoclast formation

Calcitonin effects of serum Ca and Phos

Decreased calcium | Decreased phosphate

Calcitonin effects of urine Ca and Phos

Increased calcium excretion | Increased phosphate excretion

Calcitonin: Exact role unclear as excess or deficiency do not lead to defects in bone or calcium metabolism Effect is weak

this is just a statement...

Hoe does Vit D have an effect on Ca?

Vitamin D has a potent effect to increase calcium absorption from the intestinal tract

Vitamin D has important effects on both bone _____ and bone ______

deposition | absorption

*** Vitamin D is NOT itself an active substance, but must be converted to its active product ______

1,25-dihydroxycholecalciferol

How is Vit D3 formed?

formed in the skin by exposure to sunlight

Where is vitamin D3 is converted to 1,25-dihydroxycholecalciferol at?

in the liver

GI absorption of Ca is increased by

Vit D

Urinary excretion of Calcium is decreased by _____ and enhanced by _____

PTH calcitonin

Bone resorption of calcium is increased by ____ and inhibited by _____

PTH calcitonin

How does hypoparathyroid usually happen?

Usually a result of surgical damage to the gland during thyroid surgery

After surgical removal of the parathyroid glands, when can you see a fall in calcium levels?

24-72 hours

What do low levels of Ca result in?

Tetany - calcium ion interferes with membrane transport - interferes with the relaxation of the muscle Muscle cramps Grand mal seizures Cardiovascular collapse

Treatment of hypoparathyroidism

PTH – expensive, short half life High calcium and Vit D intake Occasionally 1/25-D3 necessary

*** What happens when you have hypomag in relation to hypocalcemia?

Hypomagnesemia can cause hypocalcemia resistant to calcium Must treat first with magnesium Magnesium suppresses the release of PTH

What is primary hyperparathyroidism?

inappropriate hypersecretion of PTH resulting in hypercalcemia

What does hyperparathyroidism result in?

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

What is the most common cause of hyperparathyroidism?

parathyroid hyperplasia or parathyroid tumor

What state may stimulate the parathyroids?

pregnancy

What is Vit D deficiency usually due to?

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

What is Vit D deficiency in adults?

osteomalacia

What is Vit D deficiency in children?

Rickets: bones fail to mineralize, epiphyses fail to fuse, epiphyseal plates widen and bowing and fractures occur

One gram of Calcium Chloride contains the equivalent amount of ionized calcium as

3 grams of Calcium Gluconate

Calcium is indicated for treatment of hyperkalemia induced EKG changes because of its

cell membrane stabilizing effects

*** Calcium is indicated in patients with hypotension associated with either _____ or _____

calcium channel blockers or beta adrengergic blockers

Calcium is indicated in cases of ________ as may occur in parturients being treated for preeclampsia

magnesium toxicity

Calcium is contraindicated in patients with ______ as it may cause lethal arrhythmias

digoxin toxicity