Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

YR2: Endocrinology > Calcium + Phosphate Regulation > Flashcards

Calcium + Phosphate Regulation Flashcards

1
Q

What is the most important vitamin D metabolite?

A

1, 25-dihydroxycholecalciferol (calcitriol)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the principle effect of calcitriol?

A

Increase calcium, magnesium + phosphate absorption in the small intestines

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the other effects of calcitriol?

A

Increased reabsorption of calcium + decreased reabsorption of phosphate in the kidneys (via FGF23)
Stimulates osteoclast formation from precursors
Stimulates osteoblasts to make osteoclast-activating factors (OAFs e.g. RANKL)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does vitamin D deficiency cause? State 5 signs/ symptoms.

A 
Lack of bone mineralisation  
Softening of bone (can lead to bowing of legs) 
Bone deformities  
Bone pain 
Severe proximal myopathy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the different names for vitamin D deficiency in children and adults?

A

Children: Rickets
Adults: Osteomalacia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

State 5 causes of vitamin D deficiency.

A 
Malabsorption/ dietary insufficiency
Lack of sunlight  
Liver disease  
Renal disease 
Receptor defects
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Which step, in vitamin D metabolism, required UV light?

A

Conversion of 7-dehydrocholesterol in the skin to cholecalciferol (vitamin D3)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Describe the 2 hydroxylation reactions in vitamin D metabolism.

A

Cholecalciferol hydroxylated to form 25-hydroxycholecalciferol in the Liver
In the kidneys undergoes 2nd hydroxylation (by 1-alpha-hydroxylase) to form 1, 25-dihydroxycholecalciferol (calcitriol)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What can stimulate 1-alpha-hydroxylase in the kidneys?

A

Parathyroid Hormone (PTH)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How can lack of sunlight cause vitamin D deficiency?

A

Less 7-dehydrocholesterol is converted to cholecalciferol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How can liver disease cause vitamin D deficiency?

A

Liver is where the 1st hydroxylation takes place + where 25-hydroxycholecalciferol is stored

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How can renal disease cause vitamin D deficiency?

A

The 2nd hydroxylation step takes place in the kidneys (via 1-alpha-hydroxylase)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is usually measured to gage the level of calcitriol? Whatcondition must be fulfilled for this to be a good measure of calcitriol?

A

25-hydroxycholecalciferol

Only a good measure in the case of normal renal function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe the diagnostic characteristics of vitamin D deficiency.

A

Plasma Calcium = LOW
Plasma 25-hydroxycholecalciferol = LOW
Plasma PTH = HIGH (secondary hyperparathyroidism stimulated by the hypocalcaemia)
Plasma Phosphate = LOW
Radiological findings e.g. widened osteoid seams

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What would you expect the plasma phosphate level to be in someone with renal failure and why?

A

HIGH: because the GFR is low + there is a decrease in plasma excretion via the kidneys

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What would you expect the plasma calcium level to be in someone with renal failure and why?

A

LOW: because they are not producing as much calcitriol (due to renal failure interfering with 1-alpha hydroxylase) so there is less Ca2+ absorption in the small intestines

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the consequences of hypocalcaemia caused by renal failure?

A

Decrease in bone mineralisation + increase in bone resorption (because of an increase in PTH) leading to osteitis fibrosa cystica
Imbalance in calcium + phosphate can also lead to the formation of salts that can be deposited in extra-skeletal tissue causing extra-skeletal calcification

18
Q

What can vitamin D excess lead to?

A

Hypercalcaemia + hypercalciuria (due to increased intestinal absorption of calcium)

19
Q

What can vitamin D excess result from?

A

Excessive treatment with active metabolites of vitamin D, as in patients with chronic renal failure
Granulomatous disease: granulomatous tissue has 1-alpha-hydroxylase so it can be a source of ectopic calcitriol

20
Q

What is the treatment for primary hyperparathyroidism?

A

Parathyroidectomy

21
Q

What is the normal plasma calcium range?

A

2.2-2.6 mmol/L

22
Q

State 2 hormones that increase plasma calcium concentration.

A

Calcitriol

PTH

23
Q

What are the 2 direct effects of PTH?

A

Increased mobilisation of Ca2+ in bone

Increased Ca2+ reabsorption in the kidneys + stimulation of 1-alpha-hydroxylase

24
Q

What are the 2 direct effects of calcitriol?

A

Increased calcium absorption from the small intestine

Increased mobilisation of calcium in bone

25
Q

What can stimulate PTH release?

A

Hypocalcaemia

26
Q

State 4 signs of hypocalcaemia.

A 
Parasthesia 
Convulsions 
Arrhythmias
Tetany
(CATs go numb!)
27
Q

State 2 clinical signs of neuromuscular irritability due to hypocalcaemia.

A 
Chvostek’s Sign 
Tap the facial nerve just below the zygomatic arch
Positive = twitching of facial muscles
Trousseau’s Sign 
Inflate BP cuff for several minutes 
Induces carpopedal spasm
28
Q

State 4 causes of hypocalcaemia.

A 
Hypoparathyroidism (e.g. due to surgery, AI or magnesium deficiency) 
Vitamin D deficiency 
Pseudohypoparathyroidism  
Renal failure (impaired 1-alpha-hydroxylase)
29
Q

What are the 3 main signs and symptoms of hypercalcaemia?

A

Stones, abdominal moans + psychic groans
Stones (renal effects)
Polyuria + polydipsia
Nephrocalcinosis = deposition of calcium in the kidneys, renal colic, chronic renal failure
Abdominal moans (GI effects)
Anorexia, nausea, constipation, pancreatitis, dyspepsia
Psychic groans (CNS effects)
Fatigue, depression, impaired concentration, altered mentation, coma

30
Q

What are the 2 main causes of hypercalcaemia?

A

Primary Hyperparathyroidism (e.g. parathyroid adenoma) Malignancy (e.g. bone tumours/metastases –> increased bone turnover –> increased plasma Ca2+; tumours can also produce PTH-like peptide)

31
Q

State 2 other causes of hypercalcaemia.

A

Conditions of increased bone turnover (e.g. hyperthyroidism, Paget’s)
Vitamin D excess (rare)

32
Q

Describe how you would differentiate between primary hyperparathyroidism and malignancy causing hypercalcaemia.

A

Primary hyperparathyroidism: no negative feedback because the parathyroid adenoma will be producing PTH autonomously
Plasma Calcium = HIGH
PTH = HIGH
In malignancy, negative feedback will be intact as it is due to increased bone turnover due to bony metastases
Plasma Calcium = HIGH
PTH = LOW

33
Q

Describe the treatment of vitamin D deficiency in the case of normal renal function.

A

Give 25-hydroxy vitamin D
In inactive form of:
Ergocalciferol = 25-hydroxy vitamin D2
Cholecalciferol = 25-hydroxy vitamin D3

34
Q

Describe the treatment of vitamin D deficiency in the case of renal failure.

A

Alfacalcidol = 1-hydroxycholecalciferol

as inadequate 1-alpha-hydroxylation

35
Q

Where is phosphate reabsorbed? Via what?

A

Gut
Kidneys
Via Sodium-Phosphate transporter cells

36
Q

How does PTH effect phosphate reabsorption?

A

Inhibits sodium phosphate transporter in proximal convoluted tubule cells
Phosphate is lost in urine

37
Q

How does FGF 23 effect phosphate reabsorption?

A

Inhibits sodium phosphate transporter in proximal convoluted tubule cells
Inhibits synthesis of calcitriol, causing less phosphate absorption from gut

38
Q

Describe regulation of high serum calcium

A

Ca2+ binds to calcium sensing receptor on PTH cell

Inhibits stimulation + release of PTH secretion

39
Q

Describe regulation of low serum calcium

A

No binding to calcium sensing receptor on PTH cell
No inhibition
PTH is secreted
PTH action in body leads to increased Ca2+

40
Q

In which 2 ways may vitamin D be obtained?

A 
Through diet (Ergocalciferol- inactive)
Exposure to sunlight (UVB): stimulates synthesis of 25 OH-Vit D3
41
Q

How do changes in EC Ca2+ affect nerve + skeletal muscle excitability?

A

High: Ca2+ blocks Na+ influx, so less membrane excitability
Low: enables greater Na+ influx, so more membrane excitability

42
Q

Describe calcium, phosphate and PTH levels in primary hyperparathyroidism

A

Calcium: High
Phosphate: Low
PTH: High (unsuppressed)

YR2: Endocrinology (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions