Calcium and phosphate metabolism. Distribution of calcium and phosphate in the plasma and interstitial fluid. Bone and its relation to extracellular calcium and phosphate. Remodeling of bone

Question 1

calcium metabolism - 1

Answer 1

ORIGIN

• dietary sources = dairy/ greens/ fortified foods

Question 2

calcium metabolism - 2

Answer 2

ABSORPTION

calcium is passively absorbed in the small intestine epithelium - duodenum/ jejunum

absorption is enhanced by vitamin D which promotes calcium binding proteins

Question 3

calcium metabolism - 3

Answer 3

STORAGE

calcium is stored in bones/ teeth as hydroxypatite crystals

osteoclasts - bone remodelling
osteoblasts - bone building

Question 4

calcium regulation - x3 hormones

Answer 4

PTH
calcitonin
calcitriol = vitamin D

Question 5

PTH - origin

Answer 5

produced by parathyroid gland = behind thyroid gland

Question 6

calcium PTH - function 1

Answer 6

• increase calcium absorption when calcium is low

Question 7

calcium PTH - function 2

Answer 7

• stimulate osteoclast activity for bone resorption so calcium released into bloodstream

Question 8

calcium PTH - function 3

Answer 8

increases absorption of calcium in kidneys so less excreted in urine

Question 9

calcium PTH - function 4

Answer 9

converts cholecalciferol into calcitriol (active vitamin D)
helping calcium absorption in the gut

Question 10

calcium calcitonin - origin

Answer 10

CALCITONIN

produced by thyroid gland, parafollicular C cells

Question 11

calcium calcitonin - function 1

Answer 11

secreted by thyroid gland in response to high levels of calcium

Question 12

calcium calcitonin - function 2

Answer 12

inhibits osteoclast activity = less bone resorption = less calcium released into bloodstream

Question 13

calcium calcitonin - function 3

Answer 13

stimulates activation of vitamin D to help absorb intestinal calcium

Question 14

VITAMIN D - origin

Answer 14

cholecalciferol (inactive) converted into calcitriol (active)

Question 15

calcium VITAMIN D - function 1

Answer 15

• more calcium absorption in kidneys/ GI tract

Question 16

calcium VITAMIN D - function 2

Answer 16

involved in bone mineralisation

Question 17

phosphate metabolism - 1

Answer 17

ORIGIN
- diet = dairy/ nuts - seeds

Question 18

phosphate metabolism - 2

Answer 18

ABSORPTION

phosphate is absorbed in small intestine > jejunum

by active/ passive transport

Question 19

phosphate metabolism - 5

Answer 19

STORAGE

phosphate is stored in bones/ teeth as hydroxypatite crystals

osteoclasts - bone remodelling using phosphate

osteoblasts - bone building using phosphate

Question 20

phosphate - x3 hormones

Answer 20

PTH
fibroblast growth factor 23
vitamin D

Question 21

phosphate - PTH function 1

Answer 21

• reduce phosphate levels when they are too high

Question 22

phosphate - PTH function 2

Answer 22

• decreases osteoclast activity = less reabsorption activtiy = less phosphate in the bloodstream

Question 23

phosphate - PTH function 3

Answer 23

• decreases reabsorption in the kidney, so more phosphate excreted in urine

Question 24

phosphate - PTH function 4

Answer 24

• decreases cholecalciferol -> calctriol conversion

Question 25

FIBROBLAST GROWTH FACTOR 23 - origin

Answer 25

produced by osteocytes in response to high phosphate levels

Question 26

FIBROBLAST GROWTH FACTOR 23 - function 1

Answer 26

• reduces phosphate reabsorption in bone/ intestine

Question 27

FIBROBLAST GROWTH FACTOR 23 - function 2

Answer 27

reduces activation of vitamin D

Question 28

phosphate - vitamin D - function 1

Answer 28

cholecalciferol (inactive) converted into calcitriol (active)

Question 29

phosphate - vitamin D - function 2

Answer 29

more phosphate absorption in the kidneys / GI tract

Question 30

phosphate - vitamin D - function 3

Answer 30

involved in bone mineralisation

Question 31

distribution of calcium in plasma

Answer 31

bloodstream calcium has 3 forms:

• free ionised calcium = biologically active form
• protein-bound calcium (albumin)
• anion-bound calcium (phosphate)

bloodstream keeps calcium at 8mg/dL approx

Question 32

distribution of calcium in interstitial fluid

Answer 32

same as plasma as it equilibrates with it

Question 33

distribution of phosphate in plasma

Answer 33

bloodstream phosphate has 2 forms
- dihydrogen phosphate = H2PO4-
- hydrogen phosphate = HPO42-

bloodstream keeps phosphate at 3mgdL approx.

Question 34

distribution of phosphate in interstitial fluid

Answer 34

same as plasma as it equilibrates with it

Question 35

bone - 1

Answer 35

BONE STRUCTURE

bone matrix consists of
organic = type I collagen
inorganic = hydroxypatite crystals of calcium-phosphate

Question 36

bone - 2

Answer 36

MINERALISATION

when calcium + phosphate ions exit from ECF it forms hydroxypatite inside bone matrix

Question 37

bone - 3

Answer 37

BONE CELLS

osteoblasts = bone building
- using proteins + minerals

osteoclasts = bone resorption
- using acids + proteolytic enzymes

osteocytes = bone maturation
- using bone matrix

Question 38

bone remodelling step 1

Answer 38

osteoclasts activated upon fracture

Question 39

bone remodelling step 2

Answer 39

osteoclasts start breaking down old bone tissue to make space for new one

Question 40

bone remodelling step 3

Answer 40

osteoblasts deposit new bone containing collagen

Question 41

bone remodelling step 4

Answer 41

new bone is mineralised with calcium + phosphate to make strong/ hard

Question 42

bone remodelling mechanism - factor 1

Answer 42

AGE

old people
- less osteoblast activity = less bone building
- constant osteoclast activity = more bone resorption

Question 43

bone remodelling mechanism - factors 2

Answer 43

NUTRITION

high calcium/ vitamin D intake = better bone health

Question 44

bone remodelling mechanism - factors 3

Answer 44

wolff’s law

= bone added under mechanical high stress
= bone resorbed under mechanical low stress