Calcium homeostasis

Question 1

5 important roles of calcium in the body

Answer 1

signalling eg exocytosis, muscle contraction 
blood clotting 
apoptosis 
skeletal strength 
membrane excitability

Question 2

What does calcium do to sodium permeability?

Answer 2

decrease it

Question 3

What function of calcium is most important in the short term for homeostasis?

Answer 3

membrane excitability - sodium permeability

Question 4

Hypocalcaemia - sodium permeability and the result

Answer 4

increases sodium permeability
hyperexcitation of the neurons
tetany - spread to larynx and strap muscles can cause asphyxiation

Question 5

hypercalcaemia - sodium permeability and the result

Answer 5

decreases sodium permeability
decrease neuromuscular activity
can lead to arrhythmias

Question 6

How much of calcium is stored in bone?

Answer 6

99%

Question 7

Explain the remaining 1% of calcium in body

Answer 7

0. 9% intracellular fluid stored in mitochondria and SR

0. 1% extracellular fluid although half is bound to carrier proteins

Question 8

Is calcium in bone or ECF/ICF tightly regulated?

Answer 8

ICF/ECF

Question 9

What % of calcium in the body is free? what is the result of this?

Answer 9

0.05%

physiologically active

Question 10

How is calcium stored in bone and what does this mean?

Answer 10

hydroxyapatite - phosphate homeostasis important in calcium balance

Question 11

Does calcium have a high or low affinity to proteins and why?

Answer 11

high

small positive charge to large negative charge

Question 12

What happens to the plasma calcium ions neither bound to protein or free in solution?

Answer 12

bind to anions eg sulphate

Question 13

Is calcium binding to plasma proteins increased under acidic or alkalotic conditions?

Answer 13

alkalotic

Question 14

Explain what happens to calcium binding in hyperventilation

Answer 14

blow off more CO2
pH rises
more calcium bound to proteins
less plasma calcium = hypocalcaemic tetany

Question 15

total body calcium =

Answer 15

calcium in (diet) - calcium out ( excreted at kidneys and faeces)

Question 16

Is mechanical support or calcium balance more important in terms of the bones?

Answer 16

calcium balance

Question 17

Osteoblasts

Answer 17

bone building, active

actively lay down collagen extracellular matric which can later calcify

Question 18

Osteocytes

Answer 18

osteoblasts differentiate to form these, less active

regulate osteoblast and osteoclast activity

Question 19

Osteoclasts

Answer 19

mobilise bone by secreting H+ (pH4) to dissolve calcium salts and also provide proteolytic enzymes to digest extracellular matrix

Question 20

What are the 2 key endocrine hormones in calcium homeostasis?

Answer 20

PTH

calcitriol

Question 21

What type of hormone is PTH and where is it released from?

Answer 21

polypeptide

parathyroid glands

Question 22

What type of hormone is calcitriol? what is it the active form of? where is it produced?

Answer 22

steroid
vitamin D3
from vitamin D in liver and kidneys

Question 23

Where are parathyroid glands found and why are they important?

Answer 23

4 on posterior surface of thyroid gland - variable

essential for life so must know if they are elsewhere when removing thyroid gland

Question 24

What is PTH released in response to and what is its general action?

Answer 24

low plasma calcium

increase free calcium in the plasma

Question 25

What are some ways in which PTH works?

Answer 25

stimulate osteoclasts inhibit osteoblasts increase phosphate excretion increase reabsorption of calcium from kidney tubules to reduce calcium in urine stimulate kidney to synthesise calcitriol

Question 26

What does calcitriol promote?

Answer 26

kidney and gut absorption of calcium

Question 27

Does calcitriol complement or antagonise the action of PTH?

Answer 27

complement

Question 28

How is vitamin D activated?

Answer 28

dietary/precursors activated by sunlight

Question 29

How is calcitriol stimulated in pregnancy?

Answer 29

prolactin

Question 30

Explain the negative feedback loop of PTH and calcitriol

Answer 30

As plasma Ca rises this switches off PTH which then switches off calcitriol synthesis in the kidneys

Question 31

What does calcitriol bind to on target tissues?

Answer 31

nuclear receptors in intestine, bones, kidney

Question 32

How does calcitriol increase absorption of calcium from gut?

Answer 32

calcium from intestinal lumen to blood: calcitriol controls this active transport low plasma calcium - increase PTH, increase calcitriol and increase intestinal absorption

Question 33

3 actions of calcitriol

Answer 33

increase intestinal absorption facilitate renal absorption mobilise calcium stores by stimulating osteoclasts

Question 34

Why does prolactin stimulate calcitriol synthesis?

Answer 34

increased demand for calcium for milk production in lactation

Question 35

Value of circulating vitamin D in deficiency

Answer 35

less than 20ng/ml

Question 36

Where is vitamin D extensively stored?

Answer 36

in fat

Question 37

Risk factors for vitamin D deficiency

Answer 37

age, lack of sunlight, diet

Question 38

What is the net effect of vitamin D?

Answer 38

increase plasma calcium and mineralisation of bone

Question 39

What happens to bones in vitamin D deficiency?

Answer 39

PTH works hard to release calcium | soft and weak bones

Question 40

Children and adults vitamin D deficiency presentation

Answer 40

``` children = rickets adults = osteomalacia ```

Question 41

If you are vitamin D3 deficient what else will you be deficient in and why?

Answer 41

calcium and phosphate intestinal malabsorption leads to decreased plasma calcium which increases PTH which promotes phosphate deficiency and aggravates calcium loss from bone

Question 42

Who is most at risk of vitamin D deficiency?

Answer 42

Asian and elderly | chapatti flour, pigmented skin

Question 43

What diseases is Vitamin D deficiency implicated in?

Answer 43

arthritis, MS, cancer and CVD

Question 44

What is the 1 key hormone acts to decrease plasma calcium

Answer 44

calcitonin

Question 45

What type of hormone is calcitonin and where is it produced from?

Answer 45

peptide hormone | thyroid gland

Question 46

How does calcitonin work?

Answer 46

increased calcium in plasma binds osteoclasts and inhibits bone resorption increase renal excretion and prevent further increase in calcium

Question 47

Why is calcitonin seen as unimportant?

Answer 47

in people with calcitonin tumours or not enough they still have stable calcium levels as PTH overrides it

Question 48

When may calcitonin be used in a clinical setting?

Answer 48

Pagets disease = overactive osteoclasts

Question 49

List 5 other endocrine hormones which alter calcium balance

Answer 49

``` cortisol insulin oestrogen GH prolactin ```

Question 50

How does cortisol work to alter calcium balance?

Answer 50

inhibit osteoblasts and increase renal excretion of calcium and phosphate reduce intestinal resorption decrease plasma calcium which increases PTH and increases bone resorption osteoporosis

Question 51

Insulin effect on calcium

Answer 51

increase bone formation and antagonise cortisol | diabetics have significant bone loss

Question 52

oestrogen effect on calcium

Answer 52

promotes bone formation via oestrogen receptors on osteoblasts. Post menopausal osteoporosis

Question 53

GH effect on calcium

Answer 53

constant stimulus for bone formation

Question 54

Prolactin effect on calcium

Answer 54

promotes calcium absorption from the gut by calcitriol synthesis