Calcium and Phosphorus

Question 1

What are the functions of Calcium?

Answer 1

• NT release
• excitation-contraction coupling
• signal transduction
• enzyme cofactor
• Bone

Question 2

What are the functions of phosphorus?

Answer 2

• Buffer
• nucleic acids
• regulatory phosphorylations
• Bone

Question 3

How will hyperventilating affect calcium levels?

Answer 3

• acute alkalemia will cause more Ca to switch to bound form

- you’ll get muscle twitches and shit

Question 4

What are the three important hormones involved in regulation of blood calcium and phosphorus?

Answer 4

• PTH
• 1,25 (OH)2 Vitamin D3
• Calcitonin

Question 5

How does an increase in PTH levels affect blood calcium levels?

Answer 5

-increases blood calcium levels

Question 6

How does an increase in calcitonin levels affect blood calcium levels?

Answer 6

-decreases blood calcium levels

Question 7

Dose for dose, which hormone, PTH or calcitonin, has more potent effects on blood calcium levels?

Answer 7

-PTH

Question 8

How do parathyroid glands respond to a drop in blood calcium?

Answer 8

-increase secretion of parathyroid hormone

Question 9

What organs are directly affected by PTH?

Answer 9

• kidneys

- Bone

Question 10

What organs are indirectly affected by PTH?

Answer 10

-Intestine

Question 11

What is the effect of PTH on plasma phosphorus levels?

Answer 11

-decrease of plasma phosphorus

Question 12

What senses an increase in plasma calcium concentration? What is the response?

Answer 12

• parafollicular cells in the thyroid

- secretion of calcitonin

Question 13

What is the effect of calcitonin on the kidneys?

Answer 13

-a decrease of phosphate and calcium reabsorption, and thus an increase in the urinary excretion of calcium and phosphorus

Question 14

What is the effect of calcitonin on the bones?

Answer 14

-Decreases bone resorption and thus decreases plasma calcium levels

Question 15

What is the effect of calcitonin on plasma phosphorus levels?

Answer 15

• decreases them

- yep, same as PTH

Question 16

Where is 25-OH D3 converted to 1,25 (OH)2 D3? What enzyme catalyzes this reaction?

Answer 16

• The kidneys

- 1-alpha-hydroxylase

Question 17

What activates 1-alpha-hydroxylase?

Answer 17

• PTH
• low calcium
• low phosphorus

Question 18

What does 1,25-(OH)2 D3 do in the kidneys?

Answer 18

-increases phosphate and calcium reabsorption

Question 19

What does 1,25-(OH)2 D3 do in the intestine?

Answer 19

-increases phosphate and calcium absorption

Question 20

What does 1,25-(OH)2 D3 do in the bone?

Answer 20

-promotes the action of PTH, thus increasing plasma calcium

Question 21

What does FGF 23 do?

Answer 21

• increases phosphorus secretion in kidneys

- inhbitis 1-alpha-hydroxylase

Question 22

What does Osteoprotegerin (OPG) do?

Answer 22

-blocks the ligand (RANKL/OPGL) expressed by osteoblasts so that monocytes aren’t stimulated to differentiate into osteoclasts

Question 23

What does Sclerostin do?

Answer 23

-sent from osteocytes to osteoblasts to inhibit expression of OPGL/RANKL.

Question 24

Overall, what stimulates osteoclasts in adults?

Answer 24

• PTH
• 1,25 (OH2) D3
• Cytokines

Question 25

Overall, what inhibits osteoclasts in adults?

Answer 25

• sex steroids

- calcitonin

Question 26

What is a potential cause for a decrease in bone density in post-menopausal women?

Answer 26

-decrease in sex hormones removes inhibition of osteoclasts, which proceed to resorb more bone