Calcium homeostasis

Question 1

Is vitamin D a vitamin?

Answer 1

No, it is a hormone

Question 2

Where does the synthesis of vitamin D begin?

Answer 2

Keratinocytes in skin

Question 3

What is vitamin D synthesised from?

Answer 3

Cholesterol

Question 4

What is essential for cholesterol to be synthesised to vitamin D?

Answer 4

UV B radiation

Question 5

Where is vitamin D converted to calcidiol?

Answer 5

Liver

Question 6

Where is calcidiol converted to calcitriol?

Answer 6

Kidneys

Question 7

What is vitamin D converted to?

Answer 7

Calcidiol

Question 8

What is calcidiol converted to?

Answer 8

Calcitriol

Question 9

Which enzyme catalyses to conversion of calcidiol to calcitriol?

Answer 9

1-alphahydroxylase

Question 10

What does calcitriol do?

Answer 10

Stimulates GI tract to absorb calcium

Question 11

Flow chart for synthesis of calcitriol

Answer 11

Cholesterol -(UV B)-> vitamin D -> bloodstream -> liver -> calcidiol -> kidneys -(1-alphahydroxylase)->calcitriol

Question 12

Which hormone stimulates production of 1-alphahydroxylase?

Answer 12

PTH

Question 13

What impact does PTH have on bone?

Answer 13

Increases resorption - increases movement of calcium from bone fluid to plasma

Question 14

What impact does PTH have on kidneys?

Answer 14

Stimulates production of 1-alphahydroxylase for conversion of calcidiol to calcitriol

Question 15

Which three hormones are responsible for regulating calcium concentration?

Answer 15

Vitamin D, calcitonin, PTH

Question 16

What impact does calcitonin have on osteoclasts?

Answer 16

Inhibits activity

Question 17

What are the main causes of calcium metabolism disorders?

Answer 17

Too much/little PTH or vitamin D deficiency

Question 18

What is hypocalcemia?

Answer 18

Total calcium <2.2

Question 19

What is hypercalcemia?

Answer 19

Total calcium >2.6

Question 20

Causes of hypocalcemia

Answer 20

Hypoparathyroidism, kidney disease, hyperventilation

Question 21

Effects of hypocalcemia

Answer 21

Muscle spasms, paraesthesia, arrthymias

Question 22

Causes of hypercalcemia

Answer 22

Hyperparathyroidism, malignancy

Question 23

Effects of hypercalcemia

Answer 23

Stones - kidney stones
Bones - osteoporosis
Groans - GI symptoms - constipation etc
Moans - malaise, fatigue
Thrones - constipation
Psychiatric overtones - effects on CNS e.g. confusion

Question 24

What happens when calcium concentration gets too high?

Answer 24

C cells in thyroid produce calcitonin
Increases bone deposition
Increases calcium excretion in kidneys
Calcium levels fall

Question 25

What happens when calcium concentration gets too low?

Answer 25

Parathyroids produce PTH Increases bone resorption Acts on kidneys to produce vitamin D to increase Ca absorption in GI tract Calcium levels rise

Question 26

What impact does calcitonin have on osteoclasts?

Answer 26

Binds to receptor on them to inhibit activity

Question 27

How does PTH stimulate osteoclasts?

Answer 27

PTH binds to receptors on osteoblasts Secretes hormone called RANKL Osteoclasts have receptor for RANKL RANKL binds to osteoclasts and stimulates them to dissolve bone

Question 28

Why must phosphate be excreted?

Answer 28

Equal ratio of calcium and phosphate means that bone forms

Question 29

What impact does PTH have on the kidney?

Answer 29

Excrete phosphate, reabsorb calcium

Question 30

What impact does PTH have on the distal convoluted tubule?

Answer 30

Remove phosphate ions

Question 31

What impact does PTH have on proximal convoluted tubule?

Answer 31

Reabsorb calcium ions

Question 32

How does PTH create calcitriol?

Answer 32

Stimulates production of 1-alphahydroxylase in kidneys to convert calcidiol to calcitriol

Question 33

What does calcitriol do?

Answer 33

Increases uptake of calcium from GI tract into plasma

Question 34

What is the normal range of calcium concentration in the plasma?

Answer 34

2.2-2.6 mmol/l

Question 35

How much of the calcium in the plasma is in active form?

Answer 35

About half

Question 36

Where is calcium found?

Answer 36

Skeleton Teeth Cells Extracellular fluid

Question 37

How much calcium is stored in the skeleton?

Answer 37

99%

Question 38

How much calcium is stored in cells?

Answer 38

0.9%

Question 39

How much calcium is stored in extracellular fluid?

Answer 39

0.1%

Question 40

Function of calcium in bones

Answer 40

Hydroxyapatite crystals = strength

Question 41

Function of calcium in blood

Answer 41

Clotting cascade

Question 42

Function of calcium in endocrine system

Answer 42

Stimulus secretion coupling | Movement from extracellular fluid into cells releases hormones

Question 43

Function of calcium in muscle contraction

Answer 43

Excitation contraction coupling | Low calcium = less heart contraction = muscle failure

Question 44

Function of calcium in nervous system

Answer 44

Stimulus secretion coupling | Release of neurotransmitters from presynaptic neurones is triggered by calcium moving from fluid

Question 45

Function of calcium in secondary messenger

Answer 45

Extracellular signalling

Question 46

Function of calcium in tight junctions

Answer 46

Found between cells - the blood/brain barrier

Question 47

Roughly how much calcium do we ingest each day?

Answer 47

1000 mg

Question 48

Which two substances are the only ones whose reserves have a function in their own right?

Answer 48

Calcium and glucose

Question 49

Impacts of hypocalcaemia

Answer 49

Heart slows down or beats too rapidly Muscles go into spasm Confusion and coma

Question 50

Impacts of hypercalcaemia

Answer 50

Depression of nervous system Muscle weakness Fatigue/lethargy

Question 51

Which ethnicity has highest bone density?

Answer 51

African-americans

Question 52

What is pituitary dwarfism?

Answer 52

Under-secretion of growth hormone

Question 53

What does PTH do?

Answer 53

Increases blood calcium levels Stimulates osteoclastic bone reabsorption in response to lower ca2+ in plasma Stimulates renal production of 1,25dihyroxyvitamin D This helps reabsorb calcium from gut

Question 54

Where is 1,25dihydroxyvitamin D made?

Answer 54

Kidney

Question 55

What does 1,25dihydroxyvitamin D do?

Answer 55

Helps reabsorb calcium from gut

Question 56

What does calcitonin do?

Answer 56

Decreases blood calcium levels by inhibiting osteoclastic activity

Question 57

What does 1,25 hydroxyvitamin D do?

Answer 57

Increases synthesis of 1 alpha hydroxylase