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Endocrinology > Calcium Homeostasis > Flashcards

Calcium Homeostasis Flashcards

1
Q

What are the roles of calcium within the body?

A

Signalling - Ca2+ important signalling molecules e.g. NT’s, muscle fibres

Blood Clotting - Essential component of clotting cascade

Apoptosis

Skeletal Strength - 99% of calcium in body is wrapped up in bone where it gives strength to skeleton

Membrane Excitability - Ca2+ decreases Na+ permeability

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2
Q

What is the effect of hypocalcaemia?

A

Increased neuronal Na+ permeability leading to hyperexcitation of neurons. Can cause tetany and if it spreads to larynx/resp muscles = asphyxiation

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3
Q

What is the effect of Hypercalcaemia?

A

Decreases neuronal Na+ permeability which reduces excitability and depresses the neuromuscular activity. In extreme cases, cardiac arrhythmias

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4
Q

How is calcium distributed within the body?

A

Bones - 99%
Intracellular - 0.9%
ECF- 0.1%

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5
Q

In what form is calcium stored in the bones?

A

Hydroxyapatite

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6
Q

How much calcium is found within the plasma

A

2.2-2.6mM

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7
Q

What does calcium have a high affinity for?

A

proteins

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8
Q

How much calcium is bound to plasma within plasma?

A

~40%

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9
Q

How much calcium can be classed as “free calcium”?

A

1.2mM

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10
Q

What form of calcium is physiologically active?

A

Free calcium

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11
Q

When is binding capacity increased?

A

Under alkalotic conditions e.g. hyperventilation

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12
Q

When is binding capacity of calcium reduced?

A

When acidosis occurs

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13
Q

Define how Total Body Calcium is determined?

A

Ca2+ from diet - Ca2+ excreted in Kidneys and Faeces

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14
Q

What are osteoblasts?

A

Bone Building cells

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15
Q

What is the function of osteoblasts?

A

The lay down a collagen extracellular matrix which they then calcify

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16
Q

What do osteocytes do?

A

They control the activity of osteoblasts and osteoclasts

17
Q

What are osteoclasts?

A

Cells which are responsible for mobilising bone

18
Q

What are the functions of osteoclasts?

A

To secrete H+ ions to dissolve calcium salts and provide proteolytic enzymes to digest the extracellular matrix

19
Q

What are the two hormones which act to increase plasma calcium concentration?

A

Parathyroid Hormone - released by parathyroid gland

Calcitriol (Active form of Vit D3) steroid hormone produced from Vitamin D by the liver and kidneys

20
Q

What are the parathyroid glands?

A

4 glands which lie on the surface of the thyroid

21
Q

What is the action of PTH?

A

Stimulates osetoclasts to increase resorption of Ca2+ and phosphate in bone (Effects seen within 12-24hours)

Inhibiting osteoblasts to reduce Ca2+ deposition in bone

Increasing ReAbsorption of Ca2+

Increasing renal excretion of phosphate. This elevates free calcium concentration by preventing it from being deposited back into bone, a process that requires phosphate

Stimulates the kidney to synthesise calcitrol from Vit D which promotes calcium absorption at the gut and kidney

22
Q

What does Calcitriol do?

A

Complements action of PTH which increases calcium plasma concentration

23
Q

How is calcitriol produced?

A
  1. Liver 2. Kidneys

From vit d or precursors from sunlight in skin. Formation is stimulated by Prolactin in lactating women

24
Q

What hormone acts to decrease [Ca2+] plasma?

A

Calcitonin

25
Q

Where is calcitonin produced?

A

The thyroid gland

26
Q

What is the action of calcitonin?

A

To bind osteoclasts and inhibit bone resorption as well as increase renal excretion so preventing a further increase in Ca2+

27
Q

How does cortisol alter Ca2+ balance?

A

Inhibits osteoblasts by increasing renal excretion of Ca2+ and phosphate. Reduces intestinal absorption of Ca2+ which decreases plasma calcium which increase PTH which increases bone reorption. Produces osteoporosis

28
Q

How does insulin alter calcium balance?

A

increases bone formation and antagonises the action of cortisol

29
Q

How does oestrogen affect calcium balance?

A

Promotes bone formation via oestrogen receptors on osteoblasts

30
Q

How does GH affect calcium balance?

A

Constant stimulus for bone formation

31
Q

How does prolactin affect calcium balance?

A

Promotes calcium absorption by the gut by stimulating synthesis of calcitriol

Endocrinology (19 decks)

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