Physio: Endocrine - Calcium And Phosphate Metabolism

Front 1

What are the different forms of Ca in the body, and their relative percentages?

Back 1

40% Protein-bound, 60% ultrafilterable (10% complexed to ions, 50% free ionized)

Front 2

What is the only form of Ca which is biologically active?

Back 2

free, ionized Ca (blood conc = ~5mg/dL)

Front 3

What are the symptoms of hypocalcemia?

Back 3

hyperreflexia, spontaneous twitching, muscle cramps, tingling & numbness
specifically: Chvostek sign (twitching of facial muscles upon tapping of facial nerve), Trousseau sign (carpopedal spasm upon inflation of bp cuff)

Front 4

What are the symptoms of hypercalcemia?

Back 4

constipation, polyuria, polydipsia, lethargy, coma, death

Front 5

How does the ionized Ca concentration change when plasma protein concentration increases?

Back 5

plasma prot inc is assoc w/inc in total Ca conc, however there IS NOT a change in ionized Ca conc (because changes are slow/chronic)

Front 6

How does the ionized Ca concentration change in acidemia?

Back 6

H and Ca compete for same binding spots on albumin, thus acidemia increases ionized Ca concentration

Front 7

What is positive Ca balance?

Back 7

Intestinal a/b excedes urinary e/c, excess Ca is deposited in bones (seen in kids)

Front 8

What is negative Ca balance?

Back 8

intestinal a/b is less than Ca e/c, and deficit comes from maternal bones (often in pregnant/lactating women)

Front 9

Where is PTH synthesized?

Back 9

chief cells of parathyroid glands

Front 10

What is the stimulus for PTH secretion?

Back 10

when serum Ca is low (less than 10mg/dL) - (it is actually the ionized Ca conc that specifically regulates PTH)

Front 11

What effects do chronic changes in Ca concentration have on PTH?

Back 11

alters transcription of gene, PTH synthesis and storage, and growth of PTH glands

Front 12

What effect does Mg have on PTH?

Back 12

low Mg stimulates PTH s/c, high Mg inhibits it, but severe Mg depletion also inhibits (seen in alcoholics)

Front 13

On what 3 locations does PTH have an effect?

Back 13

bone, intestine, kidney

Front 14

What is the effect of PTH on bone?

Back 14

acts on osteoblasts briefly, but then has long-lasting effects on osteoclasts, which increases bone resorption -> releases Ca AND phosphate into ECF

Front 15

What is the urinary marker for increased bone resorption?

Back 15

hydroxyproline (released from bone matrix)

Front 16

What would be the effect if PTH ONLY acted on bone?

Back 16

none! Ca and phosphate released in equal amounts, Ca is bound, no change in ionized Ca

Front 17

What effect does PTH have on the kidney?

Back 17

1. inhibits Ph r/a (inhibit Na-Ph cotransport in proximal tubule)
2. stimulates Ca r/a in distal tubule

Front 18

What urinary markers are a result of PTH's actions on the proximal tubule?

Back 18

phosphate ("phosphaturic effect"), and cAMP

Front 19

What effect does PTH have on the intestine?

Back 19

stimulates Ca r/a indirectly via production of 1,25-dihydroxycholecalciferol (active form of vit D) in kidney

Front 20

What are the symptoms of primary hyperparathyroidism?

Back 20

inc: PTH; vit D; bone resorption; urinary Ph, cAMP, AND CA (due to high filtered load)-can cause stones; serum Ca

dec: serum Ph

Front 21

What is a common cause of primary hyperparathyroidism?

Back 21

PTH secreting parathyroid adenoma

Front 22

What is the difference between primary and secondary hyperparathyroidism?

Back 22

parathyroid gland is normal, but excessive PTH is stimulated secondary to hypocalcemia (from vit D deficiency, or renal failure)

*serum Ca is low or normal, never high*

Front 23

What are the symptoms of surgical hypoparathyroidism?

Back 23

inc: serum Ph

dec: PTH, vit D, bone resorption, Ph e/c, cAMP e/c, serum Ca

Front 24

What is a common treatment for surgical hypoparathyroidism?

Back 24

oral Ca supplement and active vitamin D

Front 25

What is the cause of pseudohypoparathyroidism?

Back 25

defective G(s) protein for PTH in kidney and bone (inherited autosomal dominant)

Front 26

What is another name for pseudohypoparathyroidism type Ia?

Back 26

Albright's hereditary osteodystrophy

Front 27

What are the physiologic changes in pseudohypoparathyroidism?

Back 27

inc: PTH, serum Ph

dec: bone resorption, serum Ca, Ph e/c, cAMP e/c

Front 28

What is the cause of humoral hypercalcemia of malignancy?

Back 28

malignant tumor that secretes PTH-related peptide (PTH-rp) (mimics actions of PTH)

Front 29

What are the physiologic changes in humoral hypercalcemia of malignancy?

Back 29

inc: serum Ca, Ph e/c, bone resorption, vit D

dec: PTH, serum Ph

Front 30

What are the common treatments for humoral hypercalcemia of malignancy?

Back 30

furosemide (inhibits renal Ca r/a, increases Ca e/c), and bone inhibitors (eg etidronate)

Front 31

What are the physiologic effects of chronic renal failure on Ca and Ph metabolism?

Back 31

*cant produce active vitamin D*

inc: PTH (secondary), serum P (caused by dec P e/c), bone resorption (due to inc PTH) w/osteomalacia (dec vit D)

dec: vit D (caused by renal failure), serum Ca (caused by dec vit D), Ph e/c (dec GFR)

Front 32

What does vitamin D deficiency in kids cause?

Back 32

rickets (growth failure and skeletal deformities)

Front 33

What does vitamin D deficiency in adults cause?

Back 33

osteomalacia (new bone fails to mineralize -> bending and softening of weight-bearing bones)

Front 34

Why is vitamin D critical to bone mineralization?

Back 34

it provides Ca and Ph to ECF

Front 35

What is the active form of vitamin D?

Back 35

1,25-dihydroxycholecalciferol

Front 36

Where is the active form of vitamin D produced, and what enzyme is it catalyzed by?

Back 36

kidney; 1alpha-hydroxylase

Front 37

What stimulates 1alpha-hydroxylase activity?

Back 37

low serum Ca, high PTH, low serum PH

Front 38

What are the actions of 1,25-dihydroxycholecalciferol in the intestine?

Back 38

increases intestinal Ca a/b (activates vit D-dependent Ca binding protein, calbindin D-28K)

Front 39

How does PTH mediate the effects of 1,25-dihydroxycholecalciferol on the intestine?

Back 39

PTH stimulates 1alpha-hydroxylase in the kidney to increase production of active vitamin D

Front 40

What are the other actions of 1,25-dihydroxycholecalciferol?

Back 40

increases intestinal Ph r/a, renal r/a of Ca and Ph, and bone resorption (to mineralize new bone)

Front 41

By what type of cells is calcitonin synthesized?

Back 41

parafollicular cells of the thyroid

Front 42

What stimulates secretion of calcitonin?

Back 42

inc serum Ca

Front 43

What the primary action of calcitonin?

Back 43

to inhibit osteoclastic bone resorption, which decreases serum Ca

note: does not participate in minute-to-minute regulation of plasma Ca

Front 44

For what syndrome could calcitonin be used as treatment?

Back 44

hypercalcemia