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Endocrine System > Endocrine Control of Calcium Balance > Flashcards

Endocrine Control of Calcium Balance Flashcards

1
Q

What is the role of calcium in the body?

A

Signalling
Blood clotting
Apoptosis
Skeletal strength
Membrane excitability

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2
Q

How does calcium effect membrane excitability?

A

Ca decreases Na permeability

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3
Q

Describe hypocalcaemia and membrane permeability

A

Increases neuronal Na permeability leading to hyperexcitation of neurons
Can cause muscle tetany
Asphyxiation - if spreads to larynx and resp. muscles

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4
Q

Describe hypercalcaemia and membrane permeability

A

Decreases neuronal Na permeability which reduces excitability and depresses neuromuscular activity and trigger cardiac arrhythmias

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5
Q

Describe calcium distribution in the body

A

99% in bones
0.9% intracellular - inside mitochondria and SR. Free Ca is low
0.1% extracellular fluid - half bound to proteins

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6
Q

What percentage of calcium is physiologically active?

A

0.05%

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7
Q

How is calcium stored in bone?

A

In calcified extracellular matrix of bone
In form of hydroxyapatite so phosphate homeostasis is important in determining calcium balance

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8
Q

How much calcium is in plasma?

A

2.2-2.6mM

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9
Q

How much calcium is bound to proteins and why?

A

Has a high affinity for protein as small positive charge attracted to large negative
40% bound

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10
Q

What does calcium bind to if not protein or free?

A

Plasma anions

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11
Q

When is binding capacity increased?

A

Under alkalotic conditions
Ex. hyperventilation - plasma pH rises so more Ca bind to proteins - giving lower Ca in plasma (hypocalcaemia tetany)

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12
Q

What happens if decrease in pH and Ca conc. in plasma?

A

Increased Ca conc. in plasma
As hydrogen ions increase and compete/ displace Ca from protein

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13
Q

How is total body calcium determined by?

A

Ca from diet
Ca excretion from kidneys and faeces
But bone and ECF is crucial

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14
Q

What is the main role of bone?

A

Role in maintaining Ca balance over mechanical support for the body

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15
Q

What is the role of osteoblasts?

A

Bone building cells
Highly active cells and lay collagen extracellular matrix which they then calcify

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16
Q

What is the role of osteocytes?

A

Osteoblasts differentiate to form these
Regulate activity of osteoblasts and osteoclasts

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17
Q

What is the role of osteoclasts?

A

Responsible for mobilising bone
Secrete H+ ions to dissolve calcium slats and provide proteolytic enzymes to digest extracellular matrix

18
Q

What 2 key hormones act to increase Ca conc. in plasma?

A

Parathyroid hormone
Calcitriol

19
Q

What hormone acts to decrease Ca conc. in plasma?

A

Calcitonin

20
Q

What is parathyroid hormone?

A

Polypeptide hormone produced by parathyroid glands - 4 glands laying on surface of thyroid gland

21
Q

What is calcitriol?

A

Active form of Vit D
Steroid hormone produced from Vit D by liver and kidneys

22
Q

What is calcitonin?

A

Peptide hormone released from parafollicular cells in thyroid gland

23
Q

When is PTH secreted?

A

When decreased free Ca conc. in plasma

24
Q

How does PTH act to increase free Ca conc. in plasma?

A

Stimulates osteoclasts to increase Ca and phosphate in bone
Inhibits osteoblasts so reduce Ca deposition
Increase reabsorption of Ca from kidney tubules so decrease excretion
Increase renal excretion of phosphate
Stimulates kidneys to synthesis calcitriol from Vit D

25
Q

Why does increasing renal excretion of phosphate help increase free Ca conc. in plasma?

A

As it stops Ca being deposited back into bone which is a process which requires phosphate

26
Q

What is the negative feedback of PTH?

A

Increased Ca conc. in plasma has negative feedback on parathyroid cell

27
Q

What is the role of calcitriol?

A

Increases Ca conc. in plasma

28
Q

What type of hormone is calcitriol?

A

Steroid hormone derived from cholesterol
Produced in 2 step process - liver then kidneys
It is enhanced by hormone prolactin in lactating women

29
Q

Describe the action of calcitriol

A

Binds to nuclear receptors in target tissues - intestine, bone and kidney
Increase absorption of Ca from gut
Facilitates renal absorption of Ca
Mobilises Ca stores of bone by osteoclasts

30
Q

How does calcitriol increase absorption of Ca from gut?

A

Active transport system which moves Ca from intestinal lumen to blood is under calcitriol control
Increased PTH then increases calcitriol which increases absorption

31
Q

What is the collective action of calcitriol?

A

Complement actions of PTH
Increase Ca conc. in plasma

32
Q

Why does prolactin stimulate calcitriol synthesis?

A

As increased demand for Ca for milk production in lactation

33
Q

Where does prolactin stimulate?

A

Stimulates kidneys to produce calcitriol

34
Q

What controls proportion of dietary calcium absorbed from intestine?

A

Circulating level of 1,25(OH)2D3 - active vit D (calcitriol)

35
Q

What is classed as Vitamin D deficiency?

A

Circulating levels fall below 20ng/ml

36
Q

What happens in Vitamin D deficiency?

A

PTH works hard to maintain Ca conc. in plasma by continually removing Ca from bone making bone soft and easily fracture
Osteomalacia and rickets

37
Q

What happens to Ca and phosphate in vitamin D deficiency?

A

Intestinal malabsorption of Ca decreases Ca conc. in blood so PTH increases which promotes phosphate deficiency which aggravates Ca loss from bone

38
Q

What condition is vitamin D implicated in?

A

MS, cancer, arthritis and CVD

39
Q

How does calcitonin decrease Ca conc. in plasma?

A

Stimulated by increase in Ca conc.
Binds to osteoclast to inhibit bone reabsorption and increases renal excretion which prevents increase

40
Q

What is XS calcitonin overridden by?

A

PTH

41
Q

What are other hormones altering Ca balance?

A

Cortisol
Insulin - increases bone formation and antagonises action of cortisol
Oestrogen/ Testosterone
GH
Prolactin

42
Q

How does cortisol affect Ca balance?

A

Inhibits osteoblasts and increases renal excretion of Ca
Also reduces intestinal absorption of Ca so decreased Ca conc. in plasma
Increases PTH so increases bone resorption
Over time get osteoporosis

Endocrine System (23 decks)

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