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Endocrine Physiology > Calcium Haemostasis > Flashcards

Calcium Haemostasis Flashcards

1
Q

Roles of calcium

A 
Signalling
Blood clotting
Apoptosis
Skeletal strength 
Membrane excitability
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2
Q

What does Ca2+ decrease the permeability of?

A

Na+

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3
Q

Hypocalcaemia effect on membrane excitability

A

Increases neuronal Na+ permeability leading to hyperexcitation of neurones

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4
Q

In extreme cases what can hypocalcaemia lead to (in respect to membrane excitability)?

A

Tetany - if spreads to larynx and resp muscles - asphyxiation

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5
Q

Hypercalcaemia effect on membrane

A

Decreases neuronal Na+ permeability which will reduce excitability and depress neuromuscular activity

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6
Q

What can hypercalcaemia trigger in extreme cases?

A

Cardiac arrhythmias

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7
Q

Distribution of calcium in the body

A

99% bones (1g)

  1. 9% intracellular fluid
  2. 1% extracellular fluid
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8
Q

Where is the calcium found in intracellular fluid?

A

Mostly stored in the mitochondria and sarcoplasmic reticulum.
Free [Ca2+]ic very low

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9
Q

Where is calcium found in the extracellular fluid?

A

Nearly half ECF Ca2+ is bound to protein

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10
Q

How much of calcium in the body is free in solution and physiologically active?

A

0.05%

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11
Q

What is most of the calcium stored in bone stored in the form of? And what does this mean is also important in determining calcium balance?

A

Hydroxyapatite

Phosphate homeostasis is also important

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12
Q

Level of calcium in the plasma

A

2.2 - 2.6mM (0.1%)

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13
Q

What does calcium have a high affinity for?

A

Proteins

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14
Q

How much of calcium is bound to plasma proteins in the plasma?

A

40%

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15
Q

Remaining 10% of plasma calcium ions that are neither bound to plasma proteins nor free are bound to what?

A

Plasma anions

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16
Q

How much of the calcium in the plasma is freely ionised and therefore physiologically active?

A

50%

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17
Q

What is the amount of calcium that is bound to protein dependent on?

A

pH of the ECF

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18
Q

What conditions does binding capacity of Ca2+ increase under?

A

Alkalotic conditions

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19
Q

What happens to calcium binding in acidosis?

A

Binding capacity reduces

Free [Ca2+] rises

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20
Q

Total body calcium = ?

A

Ca2+ from diet - Ca2+ excretion at kidney and faeces

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21
Q

Main function of bone

A

Role in maintaining Ca2+ balance

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22
Q

What does the bone do when calcium levels are low? What does this lead to?

A

Release calcium at the expense of bone strength

Leads to brittle and weak bones

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23
Q

Function of osteoblasts

A

BONE BUILDING CELLS

Lay down a collagen extracellular matrix which they then calcify

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24
Q

Function of osteocytes

A

Regulate the activity of osteoblasts and osteoclasts

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25
What do osteoblasts differentiate to form?
Osteocytes
26
Function of osteoclasts
Secrete H+ ions to dissolve the calcium salts and also provide proteolytic enzymes to digest the extracellular matrix
27
What are the two key hormones that act to increase [Ca2+]plasma?
``` Parathyroid hormone (PTH) Calcitriol ```
28
What is parathyroid hormone produced by?
Parathyroid glands
29
What is calcitriol and active form on?
Vit D3
30
What type of hormone is parathyroid hormone (PTH)?
Polypeptide hormone
31
What type of hormone is calcitriol?
Steroid hormone
32
What is calcitriol produced from and by?
From vitamin D | Liver and kidneys
33
How many parathyroid glands are there?
4
34
Where do the parathyroid glands lie?
On the posterior surface of the thyroid gland
35
What is parathyroid hormone (PTH) released in response to?
A decrease in free [Ca2+] in the plasma
36
What is done to increase free [Ca2+] by PTH?
Stimulates osteoclasts to release Ca2+ and phosphate from bone Inhibiting osteoblasts to reduce Ca2+ deposition in bone Increasing reabsorption of Ca2+ from the kidney tubules, therefore decreasing its excretion in the urine Increases renal excretion of phosphate. Stimulates the kidney to synthesise calcitriol from vitamin D
37
How long does it take for the effects to be seen from PTH stimulating osteoclasts to release Ca2+ and phosphate into bone?
12 - 24 hours
38
How does increasing the renal excretion of phosphate lead to an increased free [Ca2+] in the plasma?
It prevents Ca2+ from being deposited back into the bone, a process requiring phosphate
39
Where does calcitriol promote calcium absorption?
Gut | Kidney
40
What does calcitriol complement the action of and what does this do?
PTH | Increases [Ca2+] plasma
41
Sources of Vitamin D3
Cholesterol derivatives from UV sunlight on the skin Fatty fish e.g. tuna Fish liver oils Egg yolks
42
Formation of calcitriol from Vit D3 is stimulated by what?
Prolactin in lactating woman
43
Functions of calcitriol
Increase absorption of Ca2+ from the gut Facilitates renal absorption of Ca2+ Mobilises calcium stores in bone by stimulating osteoclast activity
44
What controls the active transport system which moves Ca2+ from the intestinal lumen to the blood?
Calcitriol
45
What does prolactin stimulate the synthesis of? Why?
Calcitriol | Increased demand for Ca2+ for milk production in lactation
46
The circulating level of what controls the proportion of dietary calcium absorbed from the intestine?
Calcitriol
47
What is the level of vitamin D to be classified as Vitamin D deficiency?
< 20ng/ml
48
Over what age is vitamin D deficiency more common in and why?
> 65 y/o | Reduced gut absorption, reduced Ca2+ mobility
49
Pathology of Vit D deficiency leading to weak bones (rickets/osteomalacia)?
``` Vit D deficiency Intestinal malabsorption of Ca2+ Decreases [Ca2+] plasma Which promotes PTH Which promotes phosphate deficiency Aggravates Ca2+ loss from bone ```
50
What two populations are most at risk of Vit D deficiency?
Elderly | Asian
51
Pigmented skin and vit D relationship
Pigmented skin less able to make vit D3 in response to UV light
52
What is vit D deficiency implicated in?
MS Cancer Arthritis CVD
53
What is the key hormone which acts to decrease [Ca2+] plasma?
Calcitonin
54
What type of hormone is calcitonin?
Peptide hormone
55
Where is calcitonin produced from?
Thyroid gland
56
What is the secretion of calcitonin stimulated by?
Increased [Ca2+] plasma
57
What is any excess of calcitonin overridden by and what does this mean?
PTH | Not important to humans really
58
Cortisol effects on bone formation
Inhibits osteoblasts, increases renal excretion of Ca2+ and phosphate and reduces intestinal absorption of Ca2+ This over time can produce osteoporosis
59
Insulin effect on bone formation
Increases bone formation | Antagonises effects of cortisol
60
Oestrogen effect on bone formation
Promotes bone formation via oestrogen receptors on osteoblasts
61
GH on bone formation
Constant stimulus for bone formation
62
Prolactin effect on bone formation
Promotes calcium absorption from the gut by stimulating synthesis of calcitriol

Endocrine Physiology (8 decks)

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