PTH, Calcium, Calcitonin

Question 1

How does hypercalcemia affect the nervous system? (3)

Answer 1

leads to progressive depression of the nervous system.

Decreases the QT interval of the heart

Depresses muscle contractility to the heart and GI tract

Question 2

How does hypocalcemia affect the nervous system

Answer 2

leads to hyper-excitability and tetany due to increased permeability to sodium and allowing easy initiation of AP’s

Question 3

What percentage of circulating calcium is ionized?

Answer 3

50%

Question 4

What is the name of the main crytsalline salt in the bone matrix

Answer 4

Hydroxyapatite

Question 5

What is a major inhibitor of calcium and phosphorus from precipitating in areas other than bone?

Answer 5

pyrophosphate

Question 6

What do osteoblasts do?

Answer 6

Deposit bone

Question 7

What does osteoclasts do?

Answer 7

Absorb bone

Question 8

Does PTH directly or indirectly stimulate osteoclasts?

Answer 8

Indirectly via inducing osteoblasts to release OPGL/RANK ligand which then converts pre-osteoclasts to osteoclasts

Question 9

What is the active form of Vitamin D3 (cholecalciferol)?

Answer 9

1-25- dihydroxycholecalciferol

Question 10

Where in the body is Vitamin D3 formed?

Answer 10

Skin after exposure to UV light

Question 11

What is the major negative feedback step that prevents excess Vitamin D3 from converting to the active form?

Answer 11

25-hydroxycholecalciferol

Question 12

Where is Vitamin D3 converted to its active form? What is required to do this?

Answer 12

Proximal tubules of the kidney

PTH

Question 13

Plasma concentrations of _____ dictate PTH secretion.

Answer 13

Calcium

Question 14

How does an increase in activated vitamin D affected calcium absorption in the intestines?

Answer 14

Increases

Question 15

What is formed in the intestinal lumen in the presence of PTH that helps transport calcium across the cell membrane?

Answer 15

calbindin

Question 16

How does PTH affect phophate absorption in the intestines?

Answer 16

Increases

Question 17

Which cells in the parathyroid gland excrete PTH?

Answer 17

Chief cells

Question 18

Explain how PTH affects calcium and phosphorus

Answer 18

PTH increases Ca resorption from distal tubules and collecting ducts

PTH increases excretion of phosphorus by diminishing reabsorption at the proximal tubule

PTH increases calcium and phosphorus absorption from bone

Net effect is increased calcium and decreased phosphorus

Question 19

Explain activated vitamin D3’s role in calcium and phosphorus

Answer 19

1-25-dihydroxycholecalciferol acts on the intestines to absorb calcium and phosphorus

Due to the activity of the kidneys, there is still a net LOSS of phosphorus in the this full loop

Question 20

What is the name of the peptide hormone that decreases plasma calcium concentrations? Where is it secreted?

Answer 20

Calcitonin, parafolliculuar C cells in the thyroid

Question 21

What is the immediate effect of calcitonin to reduce ECF calcium levels?

Answer 21

Decreases activity of osteoclasts

Question 22

What is primary hyperparathyroidism?

Answer 22

Overproduction of PTH (i.e. from a tumor in the parathyroid gland)

Question 23

What is secondary hyperparathyroidism?

Answer 23

Develops as a compensation from and disease or state that causes constant hypocalcemia

(i.e. rickets)