Regulation of Calcium and Phosphate Metabolism

Question 1

What are the processes in which Ca is involved?

Answer 1

• neurotransmission
• learning and memory
• muscle contraction
• mitosis
• mobility
• secretion
• fertilization
• blood clotting
• structure of bones and teeth

Question 2

What makes up the regulatory system to maintain extracellular fluid levels of Ca and P?

Answer 2

• vitamin D
• parathyroid hormone
• calcitonin

Question 3

Describe extracellular Ca levels.

Answer 3

• higher Ca concentration
• 50% ionized (free), 40% bound, 10% complexed in other forms(anions)

Question 4

Describe intracellular Ca levels.

Answer 4

• lower Ca concentration
• cystolic Ca can be increased as needed
• some Ca bound to proteins

Question 5

Explain Ca balance.

Answer 5

If Ca intake goes down, body adjusts by increasing percentage of Ca absorbed

Question 6

Ca-sensing is done by what receptors involved in Ca homeostasis?

Answer 6

Ca receptors on endocrine cells

Question 7

What is hypocalcemia and its effects?

Answer 7

• decrease in plasma Ca (ionized Ca)
• causes twitching/cramping of skeletal muscle
• can cause numbness/tingling (paresthesia), seizures if extreme

Question 8

What can cause hypocalcemia?

Answer 8

• lactation
• parathyroid disorders
• vitamin D disorders
• gut malabsorption of Ca
• renal failure
• ethylene glycol toxicity

Question 9

What is hypercalcemia and its effects?

Answer 9

• increase in plasma Ca (ionized Ca)
• causes constipation, polyuria, polydipsia, lethargy, coma, death

Question 10

What can cause hypercalcemia?

Answer 10

• parathyroid disorders
• vitamin D toxicity

Question 11

What can result in altering forms of Ca in plasma?

Answer 11

• changes in plasma protein concentration
• changes in complexing anion concentration
• acid-base disutrbances

Question 12

What occurs during acidemia?

Answer 12

• more H ions in blood
• more H ions bind to albumin
• free ionized Ca increases which leads to hypercalcemia

Question 13

What occurs during alkalemia?

Answer 13

• less H ions in blood
• more Ca bind to albumin
• ionized Ca in blood decreases which leads to hypocalcemia

Question 14

Intestinal absorption of Ca is regulated by what?

Answer 14

vitamin D

Question 15

Kidney reabsorption of calcium is refulated by what?

Answer 15

PTH

Question 16

Why can Ca be released into or absorbed from blood?

Answer 16

Because bone is constantly remodeled

Question 17

Describe calcium homeostasis.

Answer 17

interaction of bone, kidney, and intestine, plus parathyroid hormone, calcitonin, and vitamin D

Question 18

What substances stimulate bone reabsorption of Ca?

Answer 18

• parathyroid hormone
• vitamin D

Question 19

What substance inhibits bone reabsorption of Ca?

Answer 19

• calcitonin

Question 20

Where is phosphate stored?

Answer 20

muscle

Question 21

What ion has a fairly constant absorption from diet?

Answer 21

phosphate

Question 22

Which substance is necessary for neuromuscular transmisison?

Answer 22

magnesium

Question 23

What substance is a cofactor in enzyme reactions?

Answer 23

magnesium

Question 24

Dietary megnesium absorbed by the gut is enhances by what?

Answer 24

vitamin D

Question 25

What hormone regulates plasma Ca and P?

Answer 25

Parathyroid hormone

Question 26

What cells are the source of PTH from the parathyroid glands?

Answer 26

chief cells

Question 27

What are stimulators of PTH release?

Answer 27

- decreased blood Ca - increased blood phosphate - decreased Mg

Question 28

PTH stimulates what, which ultimately feeds back and decreases PTH secretion?

Answer 28

vitamin D

Question 29

What inihbits PTH release?

Answer 29

increased blood Ca

Question 30

PTH targets what tissues?

Answer 30

- bone - kidneys - intestines

Question 31

What are the actions of PTH?

Answer 31

- increases bone resorption to release Ca and P into blood - stimulates Ca reabsorption in distal convoluted tubule of kidney - inhibits phosphate reabsorption in proximal convoluted tubules of kidneys, thus causing P excretion in urine - increases Mg reabsorption in kidneys - stimulates vitamin D synthesis in kidneys - increases Ca absorption from intestine via vitamin D

Question 32

The primary form of hyperparathyroidism is caused by what?

Answer 32

caused by benign tumor or hyperplasia of one or both parathyroid glands

Question 33

What are clinical signs of primary hyperparathyroidism?

Answer 33

- increased PTH - hypercalcemia - hypophosphatemia - renal calculi - bone pain and fractures

Question 34

The secondary form of hyperparathyroidism is caused by what?

Answer 34

caused by increased phosphate in blood, which precipitates Ca and results in hypocalcemia which then causes secondary increase in PTH

Question 35

Secondary hyperparathyroidism may result from what?

Answer 35

renal failure or increased dietary phosphate

Question 36

Hypoparathyroidism may be caused by what?

Answer 36

- accidental surgical removal - autoimmune destruction - idiopathic

Question 37

Hypoparathyroidism results in what?

Answer 37

- decreased PTH - hypocalcemia - hyperphosphatemia

Question 38

How does calcitonin decrease blood Ca and P?

Answer 38

- inhibiting bone resorption - increasing urinary P excretion - inihbiting renal reabsorption of Ca

Question 39

What are stimulators of calcitonin?

Answer 39

- increased blood Ca - vitamin D (via feedback) - ingested food

Question 40

What sustance is required for bone formation and increases Ca absorption from GIT?

Answer 40

vitamin D

Question 41

Where is vitamin D synthesized and what form is it synthesized as?

Answer 41

synthesized in skin as precursor 7-dehydrocholesterol

Question 42

After synthesis or absorption in the gut, what happens to vitamin D in the liver?

Answer 42

- converted to 25-hydroxyvitamin D - goes to kidney -- most converted to 1,25-hihydroxyvitamin D

Question 43

Intermediates and active vitamin D are bound to what?

Answer 43

protein carriers

Question 44

What are the actions of vitamin D?

Answer 44

- stimulates Ca absorption via calbindin in intestine - stimulates absorption of phosphate and Mg in intestine - weakly stimulates Ca and P reabsorption in kidney - stimulates bone resorption in presence of PTH - increases Ca transport and uptake by SR in skeletal muscle cells - decreases PTH synthesis

Question 45

When Ca intake is low, Ca absorption is an ____ process.

Answer 45

active

Question 46

When Ca intake is high, Ca absorption is a ______ process.

Answer 46

passive