12) Calcium & phosphate regulation

Question 1

2 things that increase Ca2+ levels:

Answer 1

PTH
VIT D (calcitriol)

Question 2

How does PTH increase Ca2+ levels?

Answer 2

1) Bone-resporption
2) Kidney-increase reabsorption
3) VIT D-increased production

Question 3

How does Vit D increase Ca2+ levels?

Answer 3

Increases Ca2+ absorption in gut

Question 4

What is inactive Vit D and active Vit D also known as?

Answer 4

Inactive=25-OHD3

Active=calcitriol

Question 5

2 places phosphate is re/absorbed:

Answer 5

Kidney

Gut

Question 6

How is phosphate reabsorption in the kidney done + regulated?

Answer 6

Na+/PO43- cotransporter in PCT

-PTH & FGF23 inhibit this co-transporter

Question 7

How is phosphate absorption in the gut regulated?

Answer 7

Calcitriol increases phosphate absorption in gut

FGF23 reduces calcitriol production

Question 8

What does high PTH levels do to Ca2+ and PO43- levels?

Answer 8

High Ca2+

Low phosphate

Question 9

Where is FGF23 produced?

Answer 9

Osteocytes

Question 10

How is PTH release from parathyroid cells regulated?

Answer 10

Ca2+ sensing receptors on parathyroid cells

• high=Ca2+ binds to receptors + inhibits PTH secretion
• low=no Ca2+ binds=no inhibition so PTH secreted

Question 11

2 sources of VIT D:

Answer 11

Diet

Sun

Question 12

Where is inactive VIT D stored?

Answer 12

Liver

Question 13

Where is inactive VIT D activated and what stimulates it’s activation?

Answer 13

Kidney

PTH stimulates second hydroxylation step

Question 14

How is VIT D activation regulated?

Answer 14

Calcitriol negatively feedsback on PTH production

Question 15

5 possible causes of VIT D deficiency:

Answer 15

1) diet-lacking/malabsorption
2) lack of sun
3) liver failure-store
4) renal failure-activation
5) VIT D receptor defects

Question 16

Define VIT D deficiency:

Answer 16

lack of bone mineralisation

Question 17

What does VIT D deficiency cause in adults vs children:

Answer 17

Children=rickets

Adults=osteomalacia

Question 18

What do we measure to see if someone is VIT D deficienct?

Answer 18

Inactive vit D (25-OHD3) as calcitriol is hard to measure

Question 19

How is VIT D deficiency treated?

Answer 19

Inactive VIT D given (ergocalciferol/cholecalciferol)

Question 20

When must VIT D deficiency treatment be different to normal?

Answer 20

Renal failure-cant activate the inactive VIT D given so active VIT D should be give

Question 21

What does excess VIT D cause?

Answer 21

Hypercalemia

Question 22

2 possible causes of excess VIT D?

Answer 22

Excess treatment

Granulatomaous disease

Question 23

Compare the main effect of hypercalcemia to hypocalcemia:

Answer 23

Hypercalcemia=Ca2+ block Na2+ influx=less excitability

Hypocalcemia=Greater Ca2+ influx=more excitability

Question 24

What are the symptoms of hypercalcemia?

Answer 24

Stones, abdominal moans, psychic groans

Question 25

What are the symptoms and 2 symptoms of hypocalcemia?

Answer 25

PCAT

• parasthesia
• convulsions
• arrthymias
• tetany

Chvostek’s (face) + trosseau’s (arm)

Question 26

3 possible reasons for hypercalcemia?

Answer 26

Primary hyperthyroidism-parathyroid glands producing more PTH
Secondary hyperthyroidism-vit D deficiency
Hypercalcemia of Malignancy-PTH secretion

Question 27

2 possible reasons for hypocalcemia?

Answer 27

Low PTH

VIT D deficiency

Question 28

What is pseudohypoparathyroidism?

Answer 28

PTH resistance

Question 29

What steps should be followed when trying to diagnose hypercalcemia?

Answer 29

Observe a high Ca2+

Check PTH levels

Question 30

What are the 3 possible causes of hypercalcemia and state what the cause is and how the levels of PTH & Ca2+ are:

Answer 30

1) Primary hyperparathyroidism-parathyroid glands are producing lots of PTH
- high Ca2+, high PTH, low PO43-
- loss of -ve feedback

2) Secondary hyperparathyroidism-VIT D deficiency causes low Ca2+ so more PTH released eventually
- high Ca2+high PTH, low VIT D, low PO43-

3) Hypercalcemia of malignancy-bone cancer causing Ca2+ release
- high Ca2+, low PTH
- negative feedback still working