Lec 8 Ca

Question 1

What are the physiologic roles of Ca?

Answer 1

• maintain electronic gradient
• maintain skeletal structure
• intracellular messenger

Question 2

What are symptoms of hypercalcemia?

Answer 2

• depression
• lethargy
• coma
• muscle wekaness
• constipation

Question 3

What are symptoms of hypocalcemia?

Answer 3

• convulsions
• parasthesias
• muscle cramps
• tetany
• osteoporosis –> bone pain and pathologic fracture

Question 4

What is state of normal extracellular Ca?

Answer 4

• half bound to serum proteins [albumin]
• small amount in complex with carbonate and phosphate
• rest is free ionized Ca

Question 5

What is role of intestines in Ca hemostasis?

Answer 5

• Ca absorbed in jejunum

- amount of Ca absorbed is regulated by levels of 1,25 vit D

Question 6

What is effect of vit D level on Ca absorption?

Answer 6

higher vit D = more Ca absorption

lower vit D = less Ca absorption

Question 7

What are 3 disorders that cause high Vit D and thus high Ca?

Answer 7

• absorptive hypercalciuria
• primary hyperparathyroidism
• sarcoidosis

Question 8

What are 3 disorders associated with low vit D leading to low Ca?

Answer 8

• hypoparathyroidism
• malignancy-associated hypercalcemia
• immobilization-induced hypercalcemia

Question 9

Where is 1,25 vit D produced?

Answer 9

in kidney

Question 10

How do you calculate the filtered load of Ca?

Answer 10

multiple GFR by ionized serum CA = 10,000 mg/day

Question 11

What happens to Ca that is filtered at glomerulus?

Answer 11

90% is reabsorbed in proximal tubule

this is not regulated by Ca regulating hormones

10% goes to distal tubular sites where tightly regulated b PTH

Question 12

What is effect of PTH level on kidney regulation of Ca?

Answer 12

• does not affect reabsorption in proximal tubule

- high PTH –> increase Ca reabsorption and reduce Ca excretion in distal tubule

Question 13

What is the major means of moment-to-moment maintenance of normocalcemia?

Answer 13

PTH on distal tubule of kidney

Question 14

What is role of skeleton in Ca hemostasis?

Answer 14

• osteoclasts resorb bone –> increase blood Ca leve

Question 15

What happens to osteoblast and osteoclast activity in hyperparathyroidism?

Answer 15

both increase

Question 16

What is only exception to rule that in disease states bone turnover does not contribute or remove significant net Ca?

Answer 16

• when osteoblast/clasts become uncoupled –> immobilization hypercalcemia and malignancy-associated hypercalcemia –> have more osteoclast and less osteoblast
• PTH levels acutely rise or fall –> osteoclast activation requires hrs; osteoblast activation requires days to weeks –> acute rise in PTH leads to acute increase in osteoclastic bone resorption with net skeletal Ca loss lasting a couple weeks until osteoblast catches up

Question 17

What is normal serum Ca?

Answer 17

9.5 mg/dL

Question 18

What are 2 sources of vit D?

Answer 18

• dietary vit D supplement

- photoconversion of vit D in skin from sunlight

Question 19

How is vit D activated?

Answer 19

add two OH groups

• 1 in liver at 25 position
• 1 in prox tubule of kidney [regulated by PTH]

becomes 1,25 vit D = calcitrol

Question 20

What happens to vit D level in hyperparathyroid?

Answer 20

more activation of vit D –> more vit D avialble

Question 21

What is effect of phosphorous on vit D?

Answer 21

high serum phosphorous –> inhibits calcitrol synthesis

hypophosphatemia –> stimulates vit D synthesis

Question 22

What are two effects of vit D on Ca level?

Answer 22

• directly cause uptake of Ca from jejunal enterocyte [1ary]

- stimulate osteoclast [2ndary]

Question 23

What stimulates PTH secretion?

Answer 23

low Ca [sensed by calciusm sensing receptor [CaSR]]

Question 24

What are effects of PTH on kidney?

Answer 24

• stimulate distal tubular Ca reasborption
• stimulate conversion 25 OH D to 1,25 OH vit D
• inhibit prox tubule phosphorous reabsorption
• stimulate prox tubule cAMP synthesis and excretion

Question 25

What is TmP/GFR? What is effect of PTH on this?

Answer 25

TmP/GFR = renal tubule maximum for phosphorous

decreased wtih high PTH; increases with low PTH

Question 26

What are effects of PTH on bone?

Answer 26

• stimulates osteoclastic bone resorption

- stimulates osteoblastic bone formation

Question 27

What is mech of calcitonin?

Answer 27

high dose – >induce hypocalcemia through action of calcitonin

chronic high or low dose = no effect

Question 28

What happens in hypocalcemia?

Answer 28

• have PTH burst –> inhibits renal Ca excretion; osteoclastic bone resorption

if persists –> PTH secretion continues and vit D levels rise –> more Ca intestinal absorption; eventually osteoblasts kick in to prevent skeletal mineral loss

Question 29

How is acute vs chronic hypocalcemia corrected?

Answer 29

acute: renal Ca conservation + skeletal Ca loss
chronic: PTH induced renal Ca conservation + intestinal Ca hyperabsorption

Question 30

What is acute response to hypercalcemia?

Answer 30

inhibit PTH –> rapidly lose Ca in urine

Question 31

What is subacute/chronic response to hypercalcemia?

Answer 31

inhibit PTH –> lose Ca in urine; reduce vit D –> stop intestinal Ca absorption