Calcium Regulation

Question 1

________ are very sensitive to changes in calcium ion concentration.

Answer 1

Neurons

Question 2

Hypercalcaemia causes progressive ________ of the nervous system.

Answer 2

Depression

Question 3

Calcium is released from _______________when ______concentration decreases

Answer 3

Bones
ECF

Question 4

50% of calcium is bound to ____________.

Answer 4

Albumin

Question 5

Physiological functions expend on ____________, NOT total.

Answer 5

Ionised

Question 6

What is the preferred specimen for total Ca2+?

Answer 6

Serum or lithium heparin-plasma

Question 7

Two methods for Ca2+ detection

Answer 7

AAS - CPC and Ca2+ forms complex, Ca2+ is released from protein carrier by acidification of the sample before dye-binding reaction, uses 8-hydroxyquinoline to prevent Mg2+ interference (rarely used clinically)

ISE - membranes that selectively and reversible bind Ca2+, as Ca2+ binds electric potential develops that is proportional to ionised Ca2+ concentration

Question 8

Adjusting for albumin

Answer 8

Serum concentrations of albumin must be considered when assessing serum calcium levels
Labs use a calculation

Question 9

Negative CA2+ balance

Answer 9

Output > intake => osteoporosis

Question 10

Positive CA2+ balance

Answer 10

Intake > output => occurs during growth

Question 11

What are the three organ systems important in CA2+ metabolism?

Answer 11

Skeleton
GI tract
Kidney

Question 12

4x Calcitropic hormones

Answer 12

PTH
Vitamin D
Calcitonin
PTHrP

Question 13

PTH

Answer 13

Made in parathyroid
Tight feedback between PTH release and serum CA2+

Question 14

How many parathyroid glands do you have?

Answer 14

4

Question 15

What regulates PTH secretion?

Answer 15

Extracellular CA2+

Question 16

Low CA2+ _____________PTH

Answer 16

Increases

Question 17

CA2+ regulates transcription of PTH via _________.

Answer 17

CaSR

Question 18

High levels of ________ inhibit transcription of PTH.

Answer 18

Vitamin D3

Question 19

4 actions of PTH

Answer 19

Bone
Stimulates Ca2+-release via initial osteocyte mobilisation of Ca2+ from bone to ECF
Then continued, slow release of bone Ca2+ and phosphate from osteoclastic breakdown of bone matrix

Kidney
1. increases CA2+ reabsorption in renal tubules
2. stimulates urinary phosphate excretion
3. stimulates transcription of 1-alpha hydroxylase for vitamin D activation to active form calcitrol

Question 20

Vitamin D

Answer 20

Vit D2 => food
Vit D3 => skin via UVB rays
Promotes CA2+ absorption in GI tract and deposition in bone
Absorption greater at lower pH

Question 21

How is vitamin D activated?

Answer 21

25-hydroxylase in liver converts D3 -> D
1alpha-hydroxylase (requiring PTH) in kidney converts D -> active metabolite

Question 22

Patients with CKD fail to activate ________leading to bone disease,

Answer 22

Vitamin D

Question 23

Two stimulus for vitamin D formation

Answer 23

1. PTH
2. Low plasma phosphate

Question 24

Rickets

Answer 24

Vit D deficiency
Osteomalacia
Osteoporosis

Question 25

Vitamin D-resistant rickets

Answer 25

Deficiency of 1alpha-hydroxylase Sex linked on X-chromosome Renal tubular defect of phosphate resorption Teeth may be hypoplastic and eruption affected

Question 26

Calcitonin

Answer 26

**1.** Source Released from parafollicular C cells in the thyroid **2.** Bone Reduces rate of release of CA2+ to ECF **3.** Secretion Secreted during hypercalcemia, may protect against abnormal rises **4.** Normal physiology Minimal in normal control, if any, role in normal control of CA2+

Question 27

High calcium/vit D intake

Answer 27

PTH and active vit D are downregulated Serum calcium remains normal -> good quality bones formed

Question 28

Low calcium/vit D intake

Answer 28

PTH is upregulated Poor quality bones -> liable to fracture

Question 29

Hypocalcemia causes x3

Answer 29

Parathyroid glands don’t work Parathyroid glands work, but PTH receptor signalling doesn’t Renal failure

Question 30

Management of hypocalcaemia

Answer 30

Oral/IV calcium and correct underlying cause

Question 31

________ required for normal function of both parathyroid glands and PTH.

Answer 31

Mg2+

Question 32

Causes of Hypercalcemia

Answer 32

Multiple myeloma Hyperthyroidism Benign familial hypocalciuric hypercalcemia PTH is fully suppressed, if still detectable then hyperparathyroidism

Question 33

___________ promote urinary calcium excretion and stabilise bone

Answer 33

Bisphoshphate

Question 34

Parathyroid hormone related protein

Answer 34

PTHrP Blood calcium is increased Not sensitive to feedback regulation by CA2+

Question 35

Call ward when calcium levels

Answer 35

<1.8mmol/L >3.5mmol/L