Calcium Homeostasis

Question 1

Calcitonin is produced in ‘C-cells’ and is involved in calcium homeostasis. In which of the following are ‘C-cells’ located?

Answer 1

Thyroid gland

Question 2

There are three major hormones involved in calcium regulation. Which of the following hormones is produced in response to an elevated serum calcium concentration?

Answer 2

Calcitonin

Question 3

What is the main reservoir of calcium in the body

Answer 3

Skeleton

Question 4

Amount of calcium in skeleton

Answer 4

1200g

Question 5

Amount of calcium in extracellular space

Answer 5

1g

Question 6

Function of calcium in extracellular space

Answer 6

Muscle contractility
Nerve function
Normal blood clotting

Question 7

How is calcium in circulation

Answer 7

Ionised
Protein-bound
Complexed

Question 8

Total serum calcium

Answer 8

2.4 mmol/L

Question 9

Ionised serum calcium

Answer 9

1.1 mmol/L

Question 10

Ionised calcium

Answer 10

Metabolically active

Question 11

Protein bound calcium

Answer 11

Not metabolically active

Question 12

What is calcium complexed with

Answer 12

Citrate
Phosphate

Question 13

Modulation of ionised calcium by pH
Alkalosis

Answer 13

Higher pH- albumin more negatively charged to albumin strongly binds to calcium

Question 14

Total serum calcium at alkalosis

Answer 14

Total serum calcium unchanged

Question 15

Ionised serum calcium at alkalosis

Answer 15

Decreased

Question 16

What is low ionised calcium associated with

Answer 16

Contraction of the small muscles of the hands and feet
- tetany
There is depolarisation of the long nerves of the upper limb

Question 17

Major sources of dietary calcium

Answer 17

Dairy products
-2/3

Question 18

Minor sources of dietary calcium

Answer 18

Vegetables eg broccoli
Cereals eg white bread
Oily fish eg sardines

Question 19

Recommended intake of calcium

Answer 19

700 mg/day

Question 20

What percentage of dietary calcium do we absorb

Answer 20

30%

Question 21

Where does active absorption of calcium occur

Answer 21

Duodenum
Jejunum

Question 22

Where does passive absorption of calcium occur

Answer 22

Ileum
Colon

Question 23

When there is low availability of calcium , higher fractional excretion by

Answer 23

More active transport
Mediated by calcitriol (active form of vitamin D)

Question 24

What is the active form of vitamin D

Answer 24

Calcitriol

Question 25

Release of calcium from bone

Answer 25

Can be released rapidly from exchangeable calcium on the bone surface Can be released more slowly by osteoclasts during bone resorption

Question 26

What does the amount of calcium filtered by the glomerulus depend on

Answer 26

Glomerular filtration rate Ultrafiltrable calcium (ionised and complexed)

Question 27

What percentage of filtered calcium in the kidney is reabsorbed

Answer 27

98%

Question 28

What is reabsorption of calcium in the kidney increased by

Answer 28

Parathyroid hormone

Question 29

What is the reabsorption of calcium in the kidney decreased by

Answer 29

If filtered sodium is high

Question 30

Fractional excretion of calcium from the kidney

Answer 30

2%

Question 31

Relationship between serum calcium and parathyroid hormone

Answer 31

Small changes in serum ionised calcium causes a big change in parathyroid hormone

Question 32

Parathyroid hormone actions

Answer 32

Increases Ca2+ reabsorption Increases 1 alpha-hydroxylation of 25-OH vit D Increases bone remodelling (resorption>formation) Increases Ca2+ absorption due to increased 1,25 (OH)2 vit D

Question 33

Where is calcitonin produced

Answer 33

Thyroid C cells

Question 34

What causes the secretion of calcitonin

Answer 34

Increased serum calcium

Question 35

Effect of calcitonin

Answer 35

Lower bone resorption

Question 36

Calcitriol structure

Answer 36

Hydroxylated at positions 1 and 25

Question 37

Function of calcitriol

Answer 37

Stimulates intestinal calcium absorption

Question 38

Passive absorption of calcium in kidney

Answer 38

65% in PCT 25% in loop of henle

Question 39

Active absorption of calcium in kidney

Answer 39

8% in DCT

Question 40

Calcium sensing receptor on parathyroid gland

Answer 40

Gq coupled receptor

Question 41

Response to a low calcium diet

Answer 41

Lower serum calcium Increased parathyroid hormone secretion -exchangeable calcium released from surface of bone -decreased excretion of calcium from kidney

Question 42

Vitamin D overdose

Answer 42

Increased gut absorption of calcium Higher serum calcium Decreased PTH -decrease renal absorption of calcium -Decreased bone resorption

Question 43

Substrate for vitamin D

Answer 43

Cholesterol

Question 44

Primary production of vitamin D in skin

Answer 44

UV light on 7-dehydroxycholesterol

Question 45

Where does primary production of vitamin D occur

Answer 45

Skin

Question 46

Where is vitamin D activated

Answer 46

Kidney

Question 47

Where is vitamin d first hydroxylated

Answer 47

Liver - forms 25 -OHase

Question 48

Main function of calcitriol

Answer 48

Active gut absorption of dietary calcium

Question 49

Vitamin D synthesis

Answer 49

Can be ingested or synthesised from a cholesterol precursor: 7-dehydrocholesterol is converted into vitamin-D3 under the influence of UV radiation in the skin. In the liver, vitamin D3 is converted into 25-hydroxyvitamin D by 25-hydroxylase. In the kidney, 1-alpha-hydroxylase converts it into 1,25-dihydroxyvitamin D (calcitriol)

Question 50

Calcitriol mechanism

Answer 50

stimulates intestinal epithelial cells to increase synthesis of calbindin-D proteins which facilitate the transport of calcium from the intestinal brush border to the basolateral membrane for absorption into the blood.