:73: Calcium Metabolism

Question 1

What is the physiological normal [CA]?

Answer 1

10mg/100mL

10mg%

Question 2

How can Ca2+ be found in the blood?

Answer 2

51% ionized
46% bound to serum protein ex: albumine
3% complex w other ions

Question 3

What is the role of Ca?

Answer 3

1) muscle contraction
2) Release of hormone
3) important component of skeleton
4) Propagation of nerve impulse
5) Activation of Calmodulin which is a ubiquitous enzyme and activates other enzymes
6) Blood clotting

Question 4

What organs regulate the serum levels of Ca?

Answer 4

1) Bone (can increase Ca by osteoclasts which break bones)
2) Intestine: By increasing absorption of Ca
3) Kidney: By increasing reabsorption of Ca in distal tubules and decreasing the reabsorption of PO43- in distal and proximal tubules

Question 5

What are the Hormones that increase the levels of Ca in the blood?

Answer 5

1) Parathyroid Hormone Secreted by Parathyroid Gland

2) Vit D in its active form

Question 6

How is PTH secreted?

Answer 6

WHen Ca2+ levels decrease in the proximity of parathyroid Gland,
Increase transcription and translation of PTH
1) Pre-proPTH 110aa
2)ProPTH 90 aa
3) PTH 84 aa secreted into blood

Question 7

How is PTH affected when Ca leveles rise?

Answer 7

Decresed

Question 8

Where does PTH act directly?

Answer 8

1) Bone

2) Kidneys

Question 9

Where does PTH act indirectly?

Answer 9

Intestine through Vit D

Question 10

How does PTH act on bone

Answer 10

1) PTH binds to extracellular receptor on osteoblast
2) RANK Ligand secreted by osteoblast (osteoclast differentiating factor)
3) RANKL + Pre-Osteoclas –> Osteoclas
4) resorption of bone and increase of serum Ca2+

Question 11

How can we treat osteoporosis?

Answer 11

Antibody against RANKL

• -> Osteoclast cannot mature
• ->stop resorption of bone

Question 12

How does PTH act on kidneys?

Answer 12

Binds to receptor ion distal and proximal tubule

1) increases reabsorption of Ca in distal tubules
2) decreasing the reabsorption of PO43- in distal and proximal tubules
3) Activates 1 Hydroxylase which activates Vit D
4) Increase of cAMP in urine

Question 13

How does PTH indirectly increases reabsorption of Ca in intestine?

Answer 13

Promotes activation of Vit D in the kidney
Vit D binds to receptor on kidneys which increase Ca BP and TRPV6 (Ca Channel) Transcritpion

–> More Ca absorbed in intestines

Question 14

What is PTH gene related

Answer 14

This can cayse hypercalacemia of the tumors od kidney and lungs
PTHRP looks like PTH
–> Acts on its receptors
–> Increases levels in the serum even if we do not need it

Question 15

How can we treat Hypercalacemia of the tumor?

Answer 15

We can give&raquo_space;»»» Calcitonine (hyper physiological levels) which then decrease level of Ca by decrease resorption of bone and decreases the absorption if Ca in the intestine since calmodulin is at» levels

Question 16

Where is Calcitonin made?

Answer 16

C cells of the thyroid hormone
32 aa
In response to high [ca]

Question 17

What is the effect on Ca levels of hyperthyroidism?

Answer 17

Increase Calcitonine
Decrease Ca 2+
Problems w osteroporosis

Question 18

What happens in hypothyroidism?

Answer 18

Decrease Calcitonin
Levels of Ca remain high
Calcification!

Question 19

Where is the main action of calcitonin?

Answer 19

Bone

• -> Shrinking osteoclast
• -> less resorption
• -> less ca in the serum

Question 20

What happens at hyperphsiological [calcitonin]

Answer 20

decrease of ca reabsorption by the kidneys but that rarely happens spontaneously
usually happens when we treat hypercalacemia of the tumor by giving a high dose of calcitonin

Question 21

Where does calcitonin have no effect at all?

Answer 21

Intestine

Question 22

What does calcitonin do to stomach?

Answer 22

inhibits gastrin secretion

-> does not affect ca metabolism just another fun fact that it does

Question 23

How is vit D made?

Answer 23

From 7-dehydroxycholesterol in the skin
+ UV activation
–> Vit D3

Can also be in the diet (supplements, fish, dairy)

Question 24

How is vit D activated

Answer 24

1st) In skin w UV -> VitD3 (cholecalciferol)
2nd) in liver –> 25 (OH) D3
3rd) In kidney –> 1,25 (OH2)D3
E- 1 hydroxylase activated by PTH

Question 25

What is another name for 1,25(OH)2D3

Answer 25

Calcitriol

Question 26

Where does Vit D act?

Answer 26

1) intestine
2) Bone
3) Kidney

Question 27

Where would the Vit D receptors be?

Answer 27

Intracellular bc it is a fat soluble protein

vs extracellular for PTH

Question 28

How does Vit D act on Bone?

Answer 28

Same as PTH
Osteoblast
-> RANKL
-> Osteoclase
-> More Ca

Difference is the location of the receptor

Question 29

How does Vit D act on Intestine?

Answer 29

1) Binds to receptor = BDR intracellular
2) BDR + VIT D go to nucleus
3) Bind to promoters of TRPV6 and CaBP (CALBINDIN) increase transcription (facilitates the passage of Ca from one side of the intestine to the other)

–> Increase absorption of Ca in the intestine

Also increase absorption of phosphate in intestine

Question 30

How does Vit D act on kidney

Answer 30

It acts though receptor on distal tubules

• -> Increases action of PTH (maybe by increasing receptor making?)
• > increasing reabsorption of Ca

Question 31

Which Hormone act directly on bone?

Answer 31

PTH
PTHRP
VitD active
Calmodulin

Question 32

Which hormone act directly on intestine?

Answer 32

Activated Vit D

Question 33

Which hormone acts indirectly on intestine?

Answer 33

PTH

PTHRP

Question 34

Which hormones act directly on kidneys?

Answer 34

PTH
PTHRP
Vit D
Hyperphysiological [calmodulin]

Question 35

Which hormone does not act on intestine whatsoever?

Answer 35

Calmodulin

Question 36

What else can happen to 25(OH)D3 in the kidney?

Answer 36

It can lead to 24,25(OH)2D3 and that is an inactive intermediate