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Endocrine System > Lecture 9 Calcium Homeostasis > Flashcards

Lecture 9 Calcium Homeostasis Flashcards

1
Q

What are the roles of calcium in the body

A 
Important signalling molecules
Essential component of clotting cascade
Apoptosis
Skeletal strength
Membrane excitability
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2
Q

What does hypocalcaemia lead to within the cells

A

Increases Na+ permeability leading to hyper excitation and depolarisation leading to tetany and asphyxiation

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3
Q

What does hypercalcaemia lead to within the cells

A

Decreases Na+ permeability which reduced excitability and depress neuromuscular activity triggering cardiac arrhythmias

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4
Q

What proportion of calcium is in the bones

A

• Bones 99% (1Kg) in the form of hydroxyapatite (Ca10(PO4)6(OH)2

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5
Q

What proportion of calcium is intracellular

A

0.9% (24mM)

Mitochondria and Sarcoplamsic Reticulum

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6
Q

What proportion of calcium is in the extracellular fluid

A

0.1% (2.2.-2.6 mM)

Nearly half bound to protein

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7
Q

Define physiologically active plasma

A

Free ionised and not bound to protein

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8
Q

What effect does a high pH (alkaline) have on calcium binding to proteins

A

Increases it

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9
Q

What human function would increase pH and what effect would that have

A

Hyperventilation would increase pH and plasma concentration of calcium would fall leading to hypocalcaemic tetany

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10
Q

What human function would lead to decreased pH and what effect would that have

A

Hypoventialtion would decrease the pH and less protein would bind to calcium causing the plasma concentration to rise = hypercalcaemia

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11
Q

Total body calcium is determined by what

A

Calcium in (diet)- calcium out (kidney and faeces)

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12
Q

What is the function of osteoblasts

A

bone building cells. Highly active cells which lay down a collagen extracellular matrix which they then calcify

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13
Q

What do osteoblasts differentiate to

A

Osteocytes

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14
Q

What are osteocytes

A

less active than osteoblast but regulate the activity of osteoblasts and osteoclasts

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15
Q

What are osteoclasts

A

Responsible for mobilising bone. Secrete H+ ions to dissolved the calcium salts and also provide proteolytic enzymes to digest the extracellular matrix

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16
Q

Name 2 key hormones that act to increase calcium plasma concentration

A

PTH

Calcitriol

17
Q

How does PTH increase calcium plasma concentration

A 
Stimulate osteoclasts
Inhibit osteoblasts
Increasing reabsorption of Ca2+ from kidney tubules
Increasing renal excretion of phosphate
Stimulate kidneys to release calcitriol
18
Q

How does calcitriol complement the action of PTH

A

• Binds to nuclear receptors in target tissues (intestines, bone and kidney) to:
 Increase absorption of Ca2+ from the gut via ctaive transport

19
Q

How is calcitriol derived

A

• A steroid hormone produced in two steps (1. liver, 2. kidneys) from dietary vitamin D or from precursors activated by sunlight on skin. Formation is also stimulated by hormone prolactin in lactating women in the kidney

20
Q

In a healthy individual what percentage of calcium is absorbed

A

30%

21
Q

In a vitamin D deficient individual how much calcium is absorbed

A

10-15%

22
Q

In a pregnant individual how much calcium is absorbed

A

45-55%

23
Q

Where is vitamin d predominantly stored

A

Fat

24
Q

Vit D deficiency is more predominant in what group of people

A
  • More prevalent in >65 years due to reduce gut absorption and reduced Ca2+ mobility, and Asian
  • PTH works hard to maintain plasma calcium and in doing so continually removes calcium from bone = soft bones, growing bones become bent, easily fractured
  • Rickets in children
25
Q

What effect does calcitonin have on calcium levels

A

Produced in thyroid glands to decrease calcium in plasma. Binds to osteoclasts to inhibit bone resorption and increases renal excretion

26
Q

In thyroid tumours what happens to the calcium levels

A

Calcitonin levels are high, plasma calcium is normal as effect of calcitonin is overridden by PTH

27
Q

What effect does cortisol have on calcium

A
  • Inhibits osteoblasts
  • Increases renal excretion of calcium and phosphate
  • Reduced intestinal absorption of calcium
  • Increases PTH and bone resorption (osteoclasts break down the tissue in bones and release the minerals, resulting in a transfer of calcium from bone tissue to the blood)
28
Q

What effect does insulin have on calcium levels

A
  • Increase bone formation
  • Antagonises the action of cortisol
  • Diabetics may have significant bone loss
29
Q

What effect does oestrogen have on calcium

A
  • Promotes bone formation via oestrogen receptors on osteoblasts
  • Post-menopausal can cause osteoporosis
30
Q

What effect does GH have on calcium levels

A

Stimulus for bone formation

31
Q

What effect does prolactin have on calcium levels

A

• Promotes calcium absorption from the gut by stimulating synthesis of calcitriol

Endocrine System (26 decks)

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