Calcium

Question 1

What are the roles of calcium in the body

Answer 1

Signalling 
Blood clotting 
Apoptosis 
Skeletal strength 
Membrane excitability

Question 2

How does hypercalcaemia affect membrane excitability

Answer 2

o Hypercalcaemia decreases neuronal Na+ permeability which will reduce excitability and depress neuromuscular activity and in extreme cases, trigger cardiac arrhythmias.

Question 3

How does hypocalcaemia affect membrane excitability

Answer 3

o Hypocalcaemia increases neuronal Na+ permeability leading to hyperexcitation of neurons. In extreme cases causes tetany, if spreads to larynx and respiratory muscles – asphyxiation.

Question 4

How much total body calcium is stored in bones

Answer 4

99%

Question 5

How much total body calcium is stored intracellularly

Answer 5

0.9% (mitochondria and sarcoplasmic reticulum)

Question 6

How much total body calcium is stored extrecellularly

Answer 6

0.1%

Question 7

How much of the extracellular calcium is bound to plasma proteins

Answer 7

40%ish

Question 8

What proteins does calcium bind to

Answer 8

Globin 20%

Albumin 80%

Question 9

What is normal plasma calcium range

Answer 9

2.2-2.6mM (0.1%) (not all of this is free)

Question 10

What effect will high albumin have on plasma Ca levels

Answer 10

Decrease amount of free plasma calcium (as more is bound to albumin)

Question 11

What condition features high plasma albumin

Answer 11

Multiple myeloma

Question 12

What condition features low plasma albumin

Answer 12

Malnutrition

Nephropathy

Question 13

What effect will low albumin have on plasma Ca levels

Answer 13

Low albumin levels increase free or available calcium.

Question 14

What % of filtered calcium is reabsorbed in the kidney

Answer 14

97.99%

Question 15

What affects the total amount of calcium in the plasma

Answer 15

pH

Bones

Question 16

How does pH affect plasma calcium levels

Answer 16

Low pH increases free plasma calcium because the hydrogen ions compete with the Calcium ions for a spot on the plasma proteins

Question 17

How do bones affect plasma calcium levels

Answer 17

99% of total body Ca2+ is stored in bone and this can be added to or released as required and there is a continuous turnover of bone, it is continually being deposited and then resorbed.

Question 18

What bone cell is responsible for breaking down bone and reelaseing calcium

Answer 18

Osteoclast

Question 19

What bone cell is responsible for building bone from calcium and phosphate

Answer 19

Osteoblasts

Question 20

What is an osteocyte

Answer 20

A matured osteoblast that is less active

Question 21

How do osteoclasts mobilise bone

Answer 21

They secrete H+ ions (pH 4) to dissolve the calcium salts and also provide proteolytic enzymes to digest the extracellular matrix.

Question 22

What hormones are involved in calcium homeostasis

Answer 22

Parathyroid hormone
Calcitriol

Calcitonin

Question 23

What kind of hormone is PTH

Answer 23

polypeptide

Question 24

What kind of hormone is calcitriol

Answer 24

Steroid

Question 25

What kind of hormone is calcitonin

Answer 25

Peptide

Question 26

Where is calcitonin released from

Answer 26

The parafollicular (clear) cells of the thyroid gland

Question 27

Where are parathyroid glands located and how many are there

Answer 27

There are usually 4 lying on the posterior surface of the thyroid gland, although variations in number and location of are common, 1 in 10 people have aberrant distribution.

Question 28

How does parathyroid hormone affect Calcium levels (x5)

Answer 28

Stimulating osteoclasts to increase resorption (release) of Ca2+ and phosphate in bone Inhibiting osteoblasts thus reducing Ca2+ deposition in bone. Increasing reabsorption of Ca2+ from the kidney tubules, therefore decreasing its excretion in the urine. Increasing renal excretion of phosphate. This elevates free [Ca2+ ] by preventing it from being deposited back into bone (into hydroxyappetite), a process that requires phosphate. Stimulates the kidney to synthesise calcitriol from vitamin D which promotes calcium absorption at the gut and kidney.

Question 29

How long does it take for osteoclast stimulating effects of PTH to be seen after release

Answer 29

12-24hrs

Question 30

What is calcitriol

Answer 30

the active form of Vitamin D3

Question 31

What is calcitriols effect on calcium

Answer 31

It complements the actions of Parathyroid hormone and increases plasma calcium.

Question 32

How is calcitriol produced

Answer 32

From a two step process from inactive Vit D(cholecalciferol)

Question 33

Where does stage one of calcitriol formation occur

Answer 33

Liver

Question 34

Where does stage two of calcitriol formation occur

Answer 34

Kidneys

Question 35

What stage of calcitriol production is PTH needed

Answer 35

Stage 2 (in the kidneys)

Question 36

What hormones enhance the effect of calctriol

Answer 36

PTH | Prolactin

Question 37

How does calcitrol increase plasma calcium

Answer 37

Increase absorption of Ca2+ from the gut. Facilitates renal absorption of Ca2+ and Phophate Mobilises calcium stores in bone by stimulating osteoclast activity.

Question 38

If PTH increases phosphate excretion then why does calcitriol stimulate phosphate resabsorpion

Answer 38

To ensure any excess calcium to be laid down as bone.

Question 39

When does calcitriol Mobilises calcium stores in bone by stimulating osteoclast activity.

Answer 39

Only when calcium levels are low