Calcium, Phosphate Metabolism And Homeostasis

Front 1

What percentage of calcium is free (unbound/ionised) in serum?

Back 1

47%

Front 2

What percentage of calcium is bound to albumin in serum?

Back 2

47%

Front 3

What percentage of calcium in complexed in serum?

Back 3

6%

Front 4

Are calcium feedback mechanisms regulated by free, bound or complexed calcium?

Back 4

free

Front 5

Which fraction of calcium in serum - free, bound or complexed - is physiologically most important?

Back 5

free

Front 6

What is the normal reference range for serum calcium?

Back 6

2.2-2.6 mmol/L

Front 7

What is the equation used for adjusting calcium?

Back 7

Ca (adj) = Ca (tot) + [0.02(45-alb)]

Front 8

What are the four main organs involved in calcium homeostasis?

Back 8

Gut (GI tract)

Kidney

Bone

Parathyroid glands (calcium-sensing receptors)

Front 9

What are the three main hormones involved in calcium metabolism?

Do they increase or decrease calcium?

Back 9

parathyroid hormone - increase

1, 25 hydroxyvitamin D (calcitriol) - increase

calcitonin - decrease

Front 10

How much calcium is exchanged between bones and serum per day?

Back 10

8 mmol/day

Front 11

Approximately, how much calcium is absorbed into plasma via the gut per day?

Back 11

6 mmol/day

Front 12

How much calcium is filtered from the plasma into the kidneys per day?

How much calcium is reabsorbed from the kidneys into the plasma per day?

Back 12

240 mmol/day

234 mmol/day

Front 13

Which organ(s) does PTH act on to regulate calcium?

Back 13

Bone and kidney

Front 14

Which organ(s) does 1, 25 hydroxyvitamin D act on to regulate calcium?

Back 14

Bone and gut

Front 15

Where is most calcium absorbed in the body?

Back 15

Small intestine (duodenum and jejunum)

Front 16

Calcium is reabsorbed in different proportions at different regions of the nephron.

State where reabsoption occurs and in what percentages.

Back 16

proximal convoluted tubule (65%)

thick ascending loop of Henle (20%)

distal convoluted tubule (15%)

Front 17

Which regions of the nephron responsible for calcium reabsorption are affected by PTH and which are not?

Back 17

proximal convoluted tubule - not affected by PTH

ascending loop of Henle - affected by PTH

distal convoluted tubule - affected by PTH

Front 18

Where are the parathyroid glands located?

Back 18

Neck

Front 19

What regulated PTH secretion?

Back 19

increase/decrease of free calcium in serum

Front 20

How is calcium detected by the parathyroid glands?

Back 20

calcium-sensing receptors on the parathyroid cells

Front 21

What type of receptor is the calcium-sensing receptor?

Back 21

G protein-coupled receptor

Front 22

Which drug mimics calcium to reduce PTH concentrations?

Back 22

cinicalcet

Front 23

Describe the hormonal change which occurs when there is a small change in ionised calcium.

Back 23

Significant, inverse change in PTH

Front 24

What are the three functions of PTH

Back 24

(1) calcium reabsorption in renal tubules

(2) promotes bone resorption

(3) stimulates production of 1, 25 dihydroxyvitamin D (calcitriol) in kidney (which increases calcium absorption in the gut)

Front 25

In which organs does 1, 25 dihydroxyvitamin D (calcitriol) influence calcium homeostasis?

Back 25

Bone and gut

Front 26

In which organs does PTH influence calcium homeostasis?

Back 26

bone and kidney

Front 27

In what form is vitamin D attained from through diet and sunlight, and where is it metabolised?

Back 27

cholecalciferol (vitamin D3)

liver

Front 28

What is the product of the conversion of cholecalciferol (vitamin D3)?

Back 28

25 hydroxyvitamin D

(25 hydroxycholecalciferol)

(calcefediol)

Front 29

(1) Which form of vitamin D is converted in the liver?

(2) What form of vitamin D is it then converted to in the kidney?

Back 29

25 hydroxyvitamin D (25 hydroxycholecalciferol)(calcefediol) is converted in the liver.

It is then converted in the kidney to 1, 25 hydroxyvitamin D (1, 25 hydroxycholecalciferol) (calcitriol)

Front 30

Describe what would happen to calcium and PTH due to hyperparathyroidism

Back 30

both would increase

Front 31

Describe what would happen with the production of PTH reelated peptide due to malignancy?

Back 31

calcium increased

PTH suppressed

Front 32

What percentage of phosphate is in the mineralised matrix of bone?

Back 32

85%

Front 33

What percentage of phosphate is inorganic?

Back 33

30%

Front 34

What percentage of phosphate is found in extracellular fluids?

Back 34

1%

Front 35

Give an example of a physiological process which causes extracellular phosphate to enter cells?

Back 35

Insulin-mediated entry of glucose into cells

Front 36

What are the main organs involved in phosphate homeostasis?

Back 36

Kidney, gut and bone

Front 37

What are then main hormones involved in phosphate homeostasis?

Back 37

PTH

Fibroblast Growth Factor 23 (FGF23)

1, 25 dihydroxyvitamin D

Front 38

Roughly, how much phosphate is exchanged between the bones and plasma per day?

Back 38

7mmol/day

Front 39

Roughly, how much phosphate is exchanged between the gut and plasma per day?

Back 39

Absorbed into plasma: 32mmol/day

Released into gut: 7mmol/day

Front 40

Roughly, how much phosphate is filtered/reasbsorbed through the kidneys per day?

Back 40

Filtered: 160mmol/day

Reabsorbed: 135mmol/day

Front 41

Roughly, how much phosphate is excreted per day?

Back 41

20mmol/day

Front 42

Roughly, how much phosphate is lost in urine per day?

Back 42

25mmol/day

Front 43

What percentage of proteins is bound to proteins?

Back 43

15-20%

Front 44

Where, and in what percentages, is phosphate reabsorbed in the kidneys?

Back 44

Proximal convoluted tubule: 75-80%

Distal convoluted tubule: 20-25%

Front 45

What are the two main hormones which suppress phosphate reabsorption in the kidneys?

Back 45

PTH

Fibroblast Growth Factor 23 (FGF23)