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TSM > 1.99 Calcium Homeostasis > Flashcards

1.99 Calcium Homeostasis Flashcards

1
Q

What are calcium ions essential for?

A 
Neurotransmitter release in synapse 
Blood coagulation
Hormonal secretion - insulin and adrenal release 
Enzymatic regulation - glycolysis 
Muscle contraction
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2
Q

What percentage of calcium is found in bone?

A

99% in bone
9g bound intracellular
2g free intracellular - needs to be low or triggers biochemical reaction
1g extracellullar

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3
Q

What happens when extracellular calcium falls bellow normal?

A

The nervous system becomes hyper excitable - because of increased permeability of neuronal membranes to Na+ - this i because calcium is required for proteins in ECm to stick together - when calcium isn’t present, they don’t stick together and allow sodium to pass

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4
Q

What does hyper excitability cause?

A

Tetanic contrations

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5
Q

What is Troussaeu’s sign?

A

Hypocalceamic tetani

Inflate BP cuff above systolic for 90s, look for carpal spasm

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6
Q

In what forms is extracellular calcium present?

A

Protein bound - albumin 90%, globulins 10%
Anion complex - bicarcbonate, citrate and phosphate
Ionised

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7
Q

Which calcium is filterable at the kidney?

A

free plus anion calcium

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8
Q

How much calcium is excreted daily?

A

Diet - 1000mg

4/5 is excreted (foecal) - 800mg

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9
Q

How much calcium is absorbed from our daily diet?

A

35%

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10
Q

How much is lost through GI excretion?

A

15%

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11
Q

What percentage is lost from urine from what is absorbed in the GI?

A

Remaining 20% is lost in the urine

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12
Q

How much of the calcium filtered by the kidney is excreted?

A

only 2% of total filtered load of the kidney is lost in the urine - out of all the calcium that is filtered through the kidney - 98% is reabsorbed

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13
Q

What is the rapidly exchangeable pool?

A

Rapidly exchangeable pool - ca that exists on the surface of the bones - doesn’t remain there for very long - moving one way or another - either from ECM into bone (formation), or from bone to ECM (remodelling)

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14
Q

What are the major target organs?

A

Intestine - absorption/secretion
Kidney - filtration/absorption
Bone - formation/resorption

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15
Q

what are the two absorption pathways in the intestine?

A

Ilieum - paracellular - passive - follows concentration gradient
Transcellular - higher up in GI - active - calcium enters down the gradient - buffered by calcium binding proteins or intracellular organelles - slowly comes off these proteins and gets pumped into the blood stream by CaATPase - against conc gradient

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16
Q

What are the pros and cons of active and passive processes?

A

Passive - no rate limiting step and is not saturable - the higher conc the faster rate of transport - if theres no gradient the passive mechanism stops
Active - It has a rate limitiing step so it is saturable - the pump is the rate limiting step, cant go faster no matter how much calcium there is - however the advantage is that there will always be gradient from gi tract into the cells so it will never stop -

17
Q

What can regulate the transcellular absorption of calcium in the gut?

A

it can be regulated by hormones - vitamin D metabolites increase CaBP

18
Q

What percentage of total plasma calcium enters the kidney?

A

60% of total plasma calcium

19
Q

How is calcium absorbed in the kidney?

A

Transcellular the same was GI

30% absorbed through a passive process

20
Q

Which is the most important site of reabsorption in kidney?

A

The most important site of reabsorption is the distal tubule - because it can be regulated by the hormones
PTH and vitamin D metabolites

21
Q

In what form is calcium found in the bone?

A

Most is found in hydroxyapatite crystals - Ca10(PO4)6(OH)2

22
Q

What percentage of calcium can be released from the bone?

A

Very little Ca2+ (

23
Q

What does it mean by “bone is a dynamic tissue?

A

Bone is dynamic tissue. It is continually being formed and resorped - this is termed remodeling. 10-15% of total adult bone mass turns over each year during remodeling process

24
Q

During growth, what happens to the bone remodelling process?

A

During growth, the rate of bone formation exceeds resorption and skeletal mass increases

25
Q

Once adult bone mass is achieved, what happens to the bone remodelling process?

A

Once adult bone mass is achieved equal rates of formation and resorption maintain bone mass until age about 30 years when rate of resorption begins to exceed formation and bone mass slowly decreases

26
Q

Where does bone formation and resorption occur?

A

Trabecular bone, its simply because of the increased surface area in the middle of the bone

27
Q

What are osteoblasts?

A

Osteoblasts are the differentiated bone forming cells and secrete organic bone matrix (osteoid) on which Ca3(PO4)2 precipitates prior to full mineralization

28
Q

What is osteoid made up of?

A

Osteoid is composed primarily of collagen, mineralization is a combination of Ca3(PO4)2, OH-, and HCO3– to form mature hydroxyapatite

29
Q

How are osteocytes connected?

A

Connected to surface cells and each other via canaliculi to allow for nutrient and ion exchange

30
Q

What are osteoclasts?

A

Osteoclasts are large multinucleated cells derived from monocytes whose function is to resorb bone

31
Q

What do osteoclasts release?

A

hydrolutic and proteases

32
Q

What can increase the function of osteoclasts?

A

Parathyroid hormone

33
Q

Where is parathyroid hormone secreted?

A

PTH is synthesized and secreted by the parathyroid gland which lie posterior to the thyroid glands

34
Q

Where is the principle site of parathyroid hormone?

A

Chief cells in the parathyroid hormone

35
Q

How is PTH synthesised?

A
  • PTH is translated as a pre-prohormone (115 aa)

* Cleavage of leader and pro-sequences yield a biologically active peptide of 84 aa

36
Q

What stimulates PTH secretion?

A

The stimulus for PTH secretion is a decrease in plasma [Ca2+]

37
Q

What mechanisms of action does PTH have on bone?

A

Direct
Increases osteoclast number and activity - increase resorption
Decrease collagen synthesis by osteoblasts - decrease bone formation
Increased Ca in plasma

38
Q

What mechanisms of action does PTH have on kidney?

A

Acts directly on distal tubule to stimulate calcium reabsorption
Increases activity of 1alpha-hydroxylase, which catalyses the formation of 1,25 DHCC

39
Q

What mechanisms of action does PTH have on the intestines?

A

INDIRECT
Stimulates 1,25 DHCC synthesis (vit D metabolite)
Increase absorption of calcium

TSM (67 decks)

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