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PY352 > Calcium Homeostasis > Flashcards

Calcium Homeostasis Flashcards

1
Q

What are some intracellular roles of calcium?

A
  • muscle contraction
  • secondary messenger
  • release of neurotransmitters
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2
Q

What are some extracellular roles of calcium?

A
  • electrical excitability of cell is reduced
  • important in bone structure
  • involved in clotting
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3
Q

What is the proportion of serum calcium that is bound to unbound?

A 
Bound to plasma protein - 40%
- albumin (90%)
- globulin (10%)
Bound to anions - 10%
- phosphate
- citrate
Free calcium - 50%
- physiologically active
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4
Q

It is important to keep calcium within a tight normal range of

A

2.15-2.55mmol/L

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5
Q

If calcium levels are deranged, you will start to see

A

neurological signs

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6
Q

In hypoalbuminemia, there are low levels of ______, and thus ____ protein bound Ca++ is present, causing _____

A

albumin
less
hypocalcaemia.

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7
Q

For every 4g/L that albumin falls below 40g/L, add ____ to calcium concentration

A

0.1mmol/L

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8
Q

What are some signs + symptoms of HYPOcalcaemia?

A
  • carpopedal spasm
  • chvostek’s sign (facial spasms)
  • epileptic fits
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9
Q

What are some consequences of acute hypercalcaemia?

A
  • abdominal pain

- thirst and polyuria

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10
Q

What are some consequences of chronic hypercalcaemia?

A
  • musculoskeletal aches
  • osteoporosis
  • constipation
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11
Q

How is calcium maintained within a tight narrow range? (2.15-2.55mmol/L)

A

There are systems to decrease Ca++ and systems to increase Ca++. They ‘fight’ each other and maintain Ca++ within the tight narrow range.

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12
Q

What happens when calcium is too high?

A

When there is an increase in Ca++, the thyroid gland detects this and releases calcitonin. Calcitonin causes Ca++ to be deposited in the bones and reduces the calcium uptake in kidneys. Blood Ca++ levels then decline to set point.

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13
Q

What happens when calcium levels are too low?

A

When there is a decrease in Ca++, the parathyroid gland detects this and releases PTH. PTH stimulates the release of Ca++ from bones into the blood and stimulates Ca++ uptake in the kidneys. The kidneys release active Vit D and this increases Ca++ uptake in the intestines. Blood Ca++ levels rises to set point.

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14
Q

Which cells in the parathyroid gland make PTH?

A

Chief cells

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15
Q

How is low calcium level detected?

A
  • Less Ca++ molecules in blood
  • Calcium sensing receptor detects this
  • Modified chief cell processes
  • PTH secretion
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16
Q

PTH (Type 1 receptor), NH3 is present ________, whilst COOH is present ______

A

extracellularly

intracellularly

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17
Q

PTH activates the ____ receptor by…

The activated receptor then initiates

A

PTH/PTHrP receptor
changing its shape
a cascade of intracellular events, leading to Ca++ uptake and cAMP synthesis.

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18
Q

Where are the PTH receptors?

A

Bone

Kidneys

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19
Q

In the kidney, PTH blocks

A

the reabsorption of PHOSPHATE into the proximal tubule.

20
Q

In the kidney PTH promotes

A

calcium reabsorption into:

  • ascending LoH
  • distal tubule
  • collecting tubule
21
Q

As well as PTH, Calcium may also exert a direct affect on

A

renal reabsorption

22
Q

PTH promotes absorption of calcium from bone in 2 ways.

A
  • Rapid phase - rise in ca++ in minutes. occurs at level of osteoblasts and osteoclasts. When PTH binds to receptors on these cells, osteocytic membrane pumps ca++ from bone fluid into extracellular fluid
  • Slow phase of bone reabsorption occurs over several days and has two components. (a) osteoclasts are activated to digest formed bone (b) proliferation of osteoclasts
23
Q

Calcitonin stimulates _____ to lay down bone and therefore _____ serum calcium

A

osteoblasts

decrease

24
Q

PTH stimulates _______ to destroy bones and therefore ______ serum calcium

A

osteoclasts

increase

25
Q

Where is Vitamin D3 derived from?

A

Sun, diet (fish and meat)

26
Q

Where is Vitamin D2 derived from?

A

Food supplement

27
Q

Which Vitamin D maintains calcium balance in the body?

A

D3

28
Q

Vitamin D3 is in its ______ form when derived from the food. When it is hydroxylated, it becomes _______

A

inactive

active

29
Q

Calcidiol is the ______ form of Vit D3

A

inactivated

30
Q

The activated form of Vit D3 is called ______

A

Calcitriol

31
Q

Activated D3 increases the expression of

A

calcium binding proteins and transport proteins in the gut.

It increases gut absorption of calcium

32
Q

Hypocalcaemia is a consequence of

A

thyroid surgery

renal failure

33
Q

How may renal failure cause hypocalcaemia?

A

If renal failure, kidneys cannot convert Vit D into activated form therefore calcium cannot be absorbed by gut/ small intestine.

34
Q

How is hypocalcaemia treated if no renal failure?

A

Give calcium supplements IV calcium gluconate

35
Q

How is hypocalcaemia treated if associated with chronic renal failure

A

Give Alfacalcidol (contains activated Vit D). If Vit D is not activated then it is useless as the kidneys cannot activate it in renal failure.

36
Q

Low calcium in blood –> release of ____. This causes:

  • efflux of Ca++ from
  • decreased loss of Ca++
  • enhanced absorption of Ca++
A

PTH
bone
in urine
from intestine

37
Q

What are the two causes of hypercalcaemia?

A
  • Hyperparathyroidism

- Malignancy

38
Q

What is the treatment for hypercalcaemia?

A
  • Fluids
  • Loop diuretics not thiazides
  • Bisphosphonate (prevent loss of bone mass)
  • Calcitonin
  • Cinacalcet (lower PTH in primary hyperparathyroidism)
39
Q

Primary hyperparathyroidism is due to

A
  • hyperfunction of parathyroid glands themselves e.g. cancer of PTH gland
40
Q

Secondary hyperparathyroidism is due to

A

physiological response of PTH gland in response to hypocalcaemia, vit D deficiency (lack of sun, diet)

41
Q

What are some metabolic bone diseases?

A

Osteoporosis
Osteomalacia (rickett’s)
Paget’s Disease

42
Q

Risk factors for osteoporosis?

A
  • Taking steroids (prednisalone) >5mg o.d is a MAJOR RISK FACTOR
  • slender
  • hyperparathyroidism
  • smoker/alcoholic
  • early menopause
43
Q

Treatment for Osteoporosis?

A
  • HRT: oestrogen!
  • Vit D
  • Bisphosphonates
  • Raloxifene
  • Rarely calcitonin
44
Q

How do bisphosphonates work?

A

Bind to bone minerals in the matrix. Released slowly by osteoclasts. Accumulate in osteoclasts. Induce osteoclasts apoptosis.

45
Q

How does raloxifene work? (SERM)

A

Declining oestrogen level is a major factor in postmenopausal osteoporosis.
Oestrogen oppose the actions of PTH.
Raloxifene increases osteoblastic activity and decreases osteoclast activity

46
Q

Osteomalacia, also known as ______ is caused by

A

ricketts

- diet, malabsorption, renal disease, liver disease.

47
Q

How is osteomalacia (rickett’s) treated

A
  • Calcium with Vit D
  • Parenteral Vit D
  • (for renal disease) Alfacalcidol
  • MONITOR plasma calcium

PY352 (25 decks)

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