Lecture 61

Question 1

What are important functions of calcium?

Answer 1

1) Important structural component of the skeleton
2) Muscle contraction
3) Nerve pulse transmission
4) Blood clotting
5) Secretion of hormones –> Endocrine + Exocrine glands
6) Calmodulin

Question 2

What are functions of calmodulin?

Answer 2

1) Ca2+ binding protein
2) Found in every cell
3) Activates enzymes (ex: Ca2+ ATPase)

Question 3

What is the normal concentration of serum calcium and what are its components?

Answer 3

1) 10mg/100mL serum calcium

2) 51% Ca2+ ion, 46% Calcium complexed to proteins (such as albumin), & 3% Calcium complexed to other ions

Question 4

What are hormones that maintain calcium levels?

Answer 4

1) PTH Increases Ca2+
2) Calcitonin decreases Ca2+
3) Vitamin D increases Ca2+

Question 5

What are target tissues for calcium related hormones?

Answer 5

1) Bone
2) Kidneys
3) Intestines

Question 6

Describe 5 characteristics of PTH

Answer 6

1) 84 amino acids in length
2) 9,500 MW
3) Synthesized in parathyroid gland
4) Low Ca2+ causes increased transcription –> translation –> synthesis –> PreproPTH –> ProPTH (90aa) –> PTH (84aa) –> Released into blood from PTG
5) High Ca2+ causes: decreased transcription –> translation –> synthesis –> PTH
(auto negative feedback)

Question 7

What effect does PTH have on bone?

Answer 7

PTH increases the number of osteoclasts in bone

Question 8

Where are bone receptors for PTH located and what do they do when activated?

Answer 8

1) Receptors for PTH are on osteoblasts

2) Release RANK ligand (osteoclast differentiating factor), which converts proosteoclasts to osteoclasts (resorbs bone)

Question 9

What function does PTH have on the kidney?

Answer 9

1) Increased calcium reabsorption in the distal tubule

2) Decreased PO4 (inhibits phosphate reabsorption from proximal & distal tubules)

Question 10

What function does PTH have on the intestine?

Answer 10

1) No receptors for PTH in intestine (indirect effect)
2) When PTH acts on the kidney, it synthesizes the active form of Vitamin D, which increases calcium reabsorption in the intestine (indirect effect)

Question 11

Where can hypercalcemia malignancy occur and what are its effects?

Answer 11

1) Lung + Kidney tumors
2) Synthesize extra calcium
3) Have similar hormone to PTH called PTH Gene related peptide (PTHRP), which acts on PTH receptors

Question 12

Where is calcitonin synthesized?

Answer 12

Thyroid

Question 13

What is the approximate weight and length of calcitonin?

Answer 13

1) 3000MW

2) 32aa

Question 14

What is the function of calcitonin?

Answer 14

1) Decreases serum calcium

2) Secreted in response to Ca2+

Question 15

Where does calcitonin act and what does it do?

Answer 15

1) Acts on bone by shrinking osteoclasts
2) In kidney, it is possible for calcitonin to increase Ca2+ excretion, but only when there are supraphysiological levels of Ca2+
3) No effect of calcitonin on intestine
4) Calcitonin inhibits gastrin in the stomach

Question 16

How can one obtain vitamin D?

Answer 16

1) Fatty fish
2) Fortified dairy products
3) 7-dehydrocholesterol is converted to vitamin D by UV irradiation

Question 17

What is the function of Vitamin D binding proteins?

Answer 17

Transport Vitamin D to the liver

Question 18

What happens to vitamin D in the liver?

Answer 18

1) Vitamin D is converted to 25-hydroxy vitamin D3

2) 25-hydroxy vitamin D3 is the major circulating form of vitamin D, although it is not the active form

Question 19

What happens to 25-hydroxy vitamin D3 once it is formed?

Answer 19

1) 25-hydroxy vitamin D3 is transported to the kidney to form 1,25-dihydroxy vitamin D3 (most active form of Vitamin D, also known as calcitrol)
2) PTH helps to add hydroxyl group to position 1 (negative feeback inhibits PTH)

Question 20

What is renal osteodystrophy?

Answer 20

It is a renal disease that causes a lack of synthesis of 1,25-dihydroxy vitamin D3

Question 21

What is an alternate form of 25-hydroxy vitamin D3 that can be produced in the kidney?

Answer 21

24,25-dihydroxy vitamin D3 can be synthesized as an inactive metabolite

Question 22

Does PTHRP affect Vitamin D hydroxylase?

Answer 22

No, unlike PTH, which helps add the hydroxyl group to position 1 of 25-hydroxy Vitamin D3

Question 23

What effect does Vitamin D have on the intestine?

Answer 23

1) Vitamin D receptor is activated by 1,25-dihydroxy Vitamin D3
2) The receptor goes to the nucleus to promote transcription of calcium binding protein (Calbindin) and calcium channel protein (TRPG)

Question 24

What effect does Vitamin D have on the kidney?

Answer 24

Vitamin D enhances PTH action at the distal tubule for reabsorption of calcium

Question 25

What effect does Vitamin D have on bone?

Answer 25

1) Vitamin D increases the number of osteoclasts in bone
2) It does so by increasing synthesis of the RANK ligand through an intracellular receptor, rather than an extracellular PTH receptor