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Endocrine Physiology > Calcium and Phosphorus Homeostasis > Flashcards

Calcium and Phosphorus Homeostasis Flashcards

1
Q

What do calcium phosphate salts in bone provide?

A

Structural integrity

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2
Q

What are calcium ions in ICF and ECF responsible for?

A

Neuromuscular excitability
Blood coagulation
Hormonal secretion
Enzymatic regulation
Cell signalling

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3
Q

What is the role of PO4^3- ions in cellular processes?

A

Signal transduction

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4
Q

What is the role of PO4^3- ions in structure?

A

DNA/RNA
Membrane phospholipids
ATP/Creatine phosphate
Complex carbohydrates

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5
Q

What are 3 things does hypocalcemia cause?

A

Increased membrane Na+ permeability
Nerves and muscles become overexcitable
Involuntary muscle spasms

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6
Q

What 6 things does hypercalcemia cause?

A

Decreased neuromuscular sensitivity
Constipation
Fatigue
Bone pain
Kidney stones
Cardiac arrhythmias

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7
Q

What % of Ca2+ is found outside of the skeleton?

A

0.9% intracellular
0.1% extracellular

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8
Q

How is the extracellular concentration for calcium split up?

A

50% bound
50% free (ionised) Ca2+ bioligically active

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9
Q

What % of phosphorus is found and where?

A

80% - skeleton
15% - soft tissues
5% - plasma

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10
Q

How is the conc. of phosphorus in plasma split up?

A

85% diffusible - 35% complexed to different ions and 50% ionized
13% - non diffusible protein bound state
Remainder occurs as ATP, cAMP

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11
Q

How are Ca2+ and PO4^3- levels related?

A

Inversely related so Ca2+ X PO4^3- is constant

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12
Q

What are 3 processes that calcium phosphate play a role in?

A

Absorption
Osteocytic osteolysis
Osteoclastic resorption

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13
Q

What is precipitated on the organic collagen matrix?

A

Inorganic crystalline form of Ca2+

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14
Q

What serves as a reservoir for Ca2+ storgae?

A

Mineralized CaPO4 in bone

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15
Q

What serves as a rapidly accessible pool of Ca2+?

A

Non-mineralized CaPO4 in bone

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16
Q

What are osteoblasts?

A

Differentiated bone forming cells which secret bone matrix on which CaPO4 precipitates

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17
Q

What are osteoclasts?

A

Large multinucleated cells derived from monocytes whose function is to resorb bone

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18
Q

What are osteocytes?

A

Mature bone cells enclosed in bone matrix for bone maintenance

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19
Q

What 3 hormones regulate Ca2+ and PO4^3-?

A

Parathyroid hormone
1,25-digydroxy Vitamin D3
Calcitonin

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20
Q

What do the 3 hormones regulate?

A

Ca2+ and PO4^3- resorption, reabsorption, absorption and excretion in bone, kidney and intestine

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21
Q

What is osteocytic osteolysis?

A

Rapid exchange of calcium from pool to plasma

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22
Q

What are 3 features of osteocytic osteolysis?

A

Does not require bone resorption or decrease bone mass
Activation of PTH dependent Ca2+ pumps in osteocytic-osteoblastic membrane
Release predominatly Ca2+

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23
Q

What us osteoclastic resorption?

A

Slow exchange of Ca2+ from calcium pool to plasma

24
Q

What are 3 features of osteoclastic resorption?

A

Loss of bone mass and destruction of organic collagen matrix
Releases ca2+ and PO4^3-
Stimulated by PTH

25
Q

What is PTH?

A

Peptide hormone with high degree of evolutionary conservation

26
Q

Where is PTH secreted?

A

Parathyroid gland by chief/principal cells

27
Q

What are actions mediated by PTH receptor?

A

Type 1 - kidney and bone
Type 2 - CNS/pancreas/testis/placenta

28
Q

What us PTH related peptide protein (PTHrP)?

A

PTH like actions that has a minor role in calcium homeostasis
Secreted by many tumours

29
Q

What 3 cells are found in the parathyroid?

A

Chief cells
Oxyphil cells
Adipocytes

30
Q

What is PTH the dominant regulator of?

A

Plasma/free ionised Ca2+
Inversely related to Ca2+

31
Q

What is a trigger for PTH secretion?

A

Hypocalcaemia

32
Q

What is the Calcium Sensing Receptor?

A

G-protein coupled receptor found on chief cells and other calcium sensitive cells

33
Q

What are 2 mutations of CaSR and what do they cause?

A

activating = familial hypoparathyroidism and hypercalciuria
inactivating - familial benign hypocalciuric hypercalcemia and neonatal severe primary hyperparathyroidism

34
Q

What is the overall action of PTH?

A

Prevent/reverse hypocalcemia by increasing free plasma ca2+ levels

35
Q

How does PTH act on the bone and kidneys?

A

Bone - increase Ca2+ release
Kidneys - increase Ca2+ reabsorption and decrease PO4^3- reabsorption

36
Q

How does PTH act on the intestine?

A

Indirectly by stimulating 1.25-(OH)2-D synthesis in kidney

37
Q

What are 2 sources that Vit D is derived from?

A

Photo-dependent production in keatinocytes
Ingested in diet

38
Q

What receptors does Vit D bind to?

A

Steroid hormone family receptors

39
Q

How does Vit D circulate?

A

Complexed to Vit D binding protein

40
Q

How does Vit D play a role in calcium homeostasis?

A

Promoting intestinal Ca2+ absorption - enhances renal absorption

41
Q

How is Vit D synthesused?

A

7-dehydrocholesterol converted to Vit D3 in keratinocytes
Hydorxylated in liver to yield 25(OH)D3
2nd hydroxylation producing 1,25(OH)2D3

42
Q

What and where is the second hydroxylation of 25(OH)D3?

A

In kidney by 1 alpha hydroxylase

43
Q

What 4 ways is 1 alpha hydroxylase activity regulated?

A

Decreased Feedback inhibition of 1,25(OH)2D3
Increased PTH
Increased hypophosphatemia
Increased prolactin

44
Q

How does Vit D promote intestinal Ca2+ absorption?

A

Ca2+ bound by Vit D inducible high affinity Ca2+ binding protein called calbindin 9k

45
Q

How does calbindin work?

A

Binds 2 Ca2+ ions
Maintains favourable gradient of Ca2+ across apical membrane -> promotes reabsorption

46
Q

How does Ca2+ enter enterocytes?

A

Facilitated/active transport via specific Ca2+ transporter that is Vit D dependent

47
Q

How is PO43- absorbed in the intestine?

A

Transcellular route by a NaPO4^3- cotransporter
Downregulated by PTH

48
Q

How does Vit D promote phosphate absorption in intestine?

A

Increasing NPT2 receptors

49
Q

Where is calcitonin produced?

A

thyroid C cells (parafollicular cells)

50
Q

What are 3 physiological actions of calcitonin?

A

Inhibits osteoclastic activity in bone
Inhibits Ca2+ reabsorption by kidney
Inhibits Ca2+ by intestine

51
Q

What are 2 major stimulus’ for calcitonin secretion?

A

Increases plasma Ca2+ levels
Functional antagonist of PTH

52
Q

What are 2 causes of hyperparathyroidism?

A

85% single parathyroid adenoma
15% hyperplasia

53
Q

What are 3 symptoms of hyperparathyroidism?

A

Asymptomatic
History of kidney stones and unexpected fractures
Elevated calcium and PTH

54
Q

What are 3 causes of primary hypoparathyroidism?

A

Trauma
Idiopathic
Congenital deficiency

55
Q

What are 6 symptoms of hypoparathyroidism?

A

Fatigue
Psychological disturbances
Wheezing and dyspnea
Tetany
low or absent PTH
hypocalcemia

Endocrine Physiology (12 decks)

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