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Locomotion > Endocrine control of Ca2+ and PO4- homeostasis > Flashcards

Endocrine control of Ca2+ and PO4- homeostasis Flashcards

1
Q

What are the main physiological roles of calcium?

A 
Bone formation and teeth
Muscle contraction
Nerve function
Enzyme co-factor
Intracellular 2nd messenger
Stabilisation of membrane potentials
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2
Q

What are the main physiological roles of phosphate?

A

ATP - intracellular metabolism
Phosphorylation
Cell membrane
Buffer (acid-base)

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3
Q

How much of the total body calcium (1-2kg) is stored in bones, intracellular and extracellular?

A

Bone - 99%
Intracellular - 1%
Extracellular - 0.1%

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4
Q

How is calcium stored in plasma (2.5 mmol/l)?

A

Ionised - 45%

Bound - 55% (anions and plasma proteins)

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5
Q

What 3 hormones control calcium and phosphate homeostasis?

A 
Vitamin D (Inc calcium)
Parathyroid hormone (Inc calcium)
Calcitonin (Dec calcium)
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6
Q

What tissues/organs regulate calcium and phosphate homeostasis?

A

Kidneys
Bone
GI tract
Parathyroid glands (4)

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7
Q

What cells of the parathyroid glands are responsible for synthesising and secreting parathyroid hormone (PTH)?

A

Chief cells

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8
Q

In response to low Calcium, how does PTH affect the kidneys, bone and GI tract?

A

Bone: Inc osteoclasts
GI: Inc Ca and Po absorption
Kidneys: Inc Vit D synthesis, Inc Ca and Po reabsorption, dec Po in PCT

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9
Q

In response to low calcium, PTH increases VIt D synthesis in the kidneys. How does Vit D then affects the kidneys, bone and GI tract?

A

Bone: Inc osteoclast
Kidneys: Inc Ca and Po
GI: Inc Ca and Po absorption
Vit D also causes dec PTH due to -ve feedback

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10
Q

What cells in the thyroid gland respond to hypercalcaemia?

A

Parafollicular cells release calcitonin, in response to high calcium levels

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11
Q

What effects does calcitonin have on the kidneys, bone and GI tract?

A

Kidneys: Dec Ca and Po reabsorption
Bone: Inhibit osteoclast action
GI: nothing!

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12
Q

What 2 ways does the body produce/absorb Vit D?

A

Skin: Produces D3 (colecalciferol) (90%)
Diet: Absorb D2 and D3 (10%)

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13
Q

How is Vit D synthesised from the liver?

A

D3 is converted to 25(OH)D - Calcidiol by alpha1hydroxylase
This is then converted to 1,25(OH)D - Calcitriol by hydroxylase
(Can be inactivated by 24 hydroxylase)

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14
Q

What is the mechanism by which low calcium increases PTH?

A

Decreased CaSR (calcium sensing receptor) signalling: Dec cAMP and dec production & secretion PTH

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15
Q

What is the mechanism by which high calcium decreases PTH?

A

Ca+CaSR activates PLC - suppression of PTH secretion and gene expression.
activation iG-protein signalling, inhibits AC, dec cAMP, inc suppression PTH production.

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16
Q

What is PTHrP and what does it do? (parathyroid hormone related peptide)

A

Mimics PTH and elevates calcium levels

can be produced by some cancers/tissues

17
Q

Which part of the intestine does calcium absorption occur?

A

Duodenum and jejunum

18
Q

How is calcium absorbed in the GI tract?

A 
Paracellular route (Ca and CaBP)
Active uptake (TRPV6) and extrusion (CaATPase)
Endocytosis (TRPV6) and exocytosis of Ca/CaBP complex
19
Q

How is phosphate absorbed in the intestine?

A

NPT2b major transporter intestine
Increased by 1,25D and low dietary PO4
Inhibited by high dietary PO4

20
Q

How does calcium reabsorption occur in the distal tubule?

A

PTH and vitamin D up-regulate luminal Ca2+ channels (TRPV5) and basolateral Ca2+ efflux transporters.

21
Q

How does PTH dec phosphate reabsorption in the Proximal convoluted tubule?

A

PTH increases urinary phosphate excretion by reducing NaPi-dependent phosphate uptake in the proximal tubular epithelial cells

22
Q

What are the S&S of hypercalcaemia? (Bones, stones and groans)

A 
Osteoporosis
Shortened QT
Polydipsia/Polyuria
Muscle weakness
Kidney stones
23
Q

What are the S&S of hypocalcaemia?

A 
Tetany - muscle spasms
Long QT
Carpopedal spasm
Paraesthesia
Seizures
24
Q

What can cause hypercalcaemia?

A

Bone erosion by malignancy

Primary (1) hyperparathyroidism

25
Q

What can cause hypocalcaemia?

A

Vit D deficiency
Hypoparathyroidism
CKD

26
Q

How can you treat hypercalcaemia? (Ca Levels Above Preferred Figures)

A 
Calcitonin
Loop Diuretic (Furosemide)
Alendronic acid (Bisphosphonates)
Parathyroid gland removal
Fluids
27
Q

How can you treat hypocalcaemia?

A

Acute - give IV calcium gluconate

Chronic - Vit D and Calcium

28
Q

Primary hyperparathyroidism can be caused due to an adenoma releasing high levels of PTH, what effects does this have on PTH, Calcium and phosphate?

A

PTH - high
Calcium - high
Phosphate - low

29
Q

Secondary hyperparathyroidism can be caused due to low levels of calcium (Vit D deficiency), what effects does this have on PTH, Calcium and phosphate?

A

PTH - high
Clacium - low
Phosphate - normal or high

30
Q

Tertiary hyperparathyroidism can be caused due to long periods of secondary HyperPTism (kidney issues), what effects does this have on PTH, Calcium and phosphate?

A

PTH - very high
Clacium - high
Phosphate - high

Locomotion (26 decks)

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