Brainscape's Knowledge GenomeTM

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


See full index

BRS Endocrinology > Regulation of Calcium and Phosphate > Flashcards

Regulation of Calcium and Phosphate Flashcards

1
Q

What is the most abundant metal in the body?

A

calcium

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

How is calcium distributed in the body?

A

99% resides in skeleton and teeth as calcium hydroxyapatite crystals
Extracellular calcium (tiny amount of total body calcium) is tightly regulated
‘Unbound’ ionised calcium = biologically active component

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

What is extracellular calcium?

A

In plasma
- ionised Ca (45%)
- Bound Ca2+

Bound Ca2+= Plasma proteins (45%) or anions (bicarbonate, phosphate, lactate)

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

What increases serum calcium and phosphate and what do they act on?

A

Parathyroid hormone (PTH) (secreted by parathyroid glands)

Vitamin D
Synthesised in skin or intake via diet

Main regulators of calcium & phosphate homeostasis via actions on kidney, bone and gut

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

What decreases serum calcium and phosphate?

A

Calcitonin (secreted by thyroid parafollicular cells)

  • Can reduce calcium acutely, but no negative effect if parafollicular cells are removed eg thyroidectomy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are sources of vitamin D?

A

D2= ergocalciferol derived from UV irradiation of plants

D3= cholecalciferol derived from UV irradiation of skin (animals and humans) and certain foods (oily fish, egg yolks)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe vitamin D metabolism.

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

What is the active form of vitamin D called?

A

calcitriol

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

How does the sun make vitamin D3 (cholecalciferol)?

A

7-dehydrocholesterol
-> pre-vitamin D3
-> cholecalciferol (D3)

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

How does 1,25(OH)2 cholecalciferol regulate its own synthesis?

A

by decreasing transcription of 1 alpha- hydroxylase

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

What is the major role of calcitriol?

A

Increase Ca2+ and PO4(3-) reabsorption from the GUT

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

What is the effect of calcitriol in 3 major parts of the body?

A

Gut= increase Ca2+ and PO4(3-) reabsorption from the gut

kidney= increase Ca2+ and PO4 reabsorption

bone= increase Ca2+ reabsorption

Overall= Increase Ca2+ in blood

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

What is calcitriol?

A

1,25(OH)2 cholecalciferol (active form of vitamin D)

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

What secretes parathyroid hormone?

A

Chief cells in the parathyroid glands

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

How is parathyroid hormone secreted?

A

Secreted as a large precursor (pre-pro-PTH) & cleaved to PTH

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

What triggers parathyroid hormone secretion?

A

G-protein coupled calcium sensing receptor on chief cells detects change in circulating calcium concentration

PTH secretion inversely proportional to serum calcium (aka if Ca is low PTH is up)

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

How do the calcium sensing receptors work?

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

When serum calcium increases, what happens to parathyroid hormone (PTH)?

A

It decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the actions of parathyroid hormone (PTH) on 3 parts of the body?

A

Gut bone and kidney

Overall increased plasma Ca2+

Most of the time PO4 loss is greater than absorption, so overall PO4 is lost

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How does PTh affect bone strength?

A

It decreases as Ca2+ is released

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what are osteoblasts and osteoclasts?

A

osteoblast= build bone
osteoclast= consume bome

22
Q

What is the PTH action in bone?

A

PTH binds to PTH receptor on osteoblast

This triggers osteoclast activating factors
- OAFs (e.g. RANKL; Receptor activator of nuclear factor kappa-B ligand)

This leads to osteoclasts consuming bone and bone reabsorption

23
Q

What is the effect of calcitriol in bone?

A

Calcitriol effects on bone depend on serum calcium:

LOW serum calcium – calcitriol works with PTH to increase calcium reabsorption from bone
osteoclasts > osteoblasts

NORMAL serum calcium – calcitriol promotes bone formation
osteoblasts > osteoclasts

Bone RESORPTION

24
Q

How is PTH regulated?

A

Increased plasma Ca2+ produces a negative feedback loop

25
Q

What is calcitonin?

A

Secreted from parafollicular (C) cells of the thyroid gland
Reduces serum calcium
Physiological role in calcium homeostasis in humans unclear
Removal of thyroid gland does not affect serum calcium

26
Q

Where is PTH stored?

A

colloid

27
Q

What are the actions and regulations of calcitonin?

A
28
Q

What are the cells in the proximal convoluted tubule of the kidney?

A

Cuboidal epithelia

29
Q

How does PO4(3-) enter cuboidal epithelia of PCT from the filtrate?

A

Na+PO4(3-) co-transporter
Na+ enters at the same time

30
Q

What inhibits Na+PO4 co-transporter?

A

FGF23

FGF23 gene provides instructions for making a protein called fibroblast growth factor 23

31
Q

How does FGF23 inhibit Na+PO4- co-transporter?

A

Inhibits calcitriol

32
Q

Where is FGF23 found?

A

In the cuboidal epithelial cells of the PCT

33
Q

Describe the regulation of serum phosphate by FGF23.

A
34
Q

What effect does calcitriol have on serum phosphate?

A

calcitriol increases PO4(3-) reabsorption

Increases serum phosphate (and calcium)

35
Q

What is high serum calcium?

A

Hypercalcaemia

36
Q

What is low serum calcium?

A

Hypocalcaemia

37
Q

What does hypercalcaemia cause when it comes to action potentials?

A

Action potential generation in nerves/skeletal muscle requires Na+ influx across cell membrane

HYPERcalcaemia= high extracellular Ca=
Ca2+ blocks Na+ influx, so LESS membrane excitability

38
Q

What does hypocalcaemia cause when it comes to action potentials?

A

enables GREATER Na+ influx, so MORE membrane excitability

39
Q

what does hypocalcaemia cause and what it the mnemonic to remember?

A

Sensitises excitable tissues; muscle cramps, tetany, tingling
- muscle and nerve types of cells
- muscles can contract but can’t relax properly

Signs & symptoms
Paraesthesia (hands, mouth, feet , lips)

Convulsions
Arrhythmias
Tetany
Mnemonic - [CATs go numb]

40
Q

What are 2 tests for a sign of hypocalcaemia?

A

Chvostek’s sign

Tap facial nerve just below zygomatic arch
Positive response = twitching of facial muscles
Indicates neuromuscular irritability due to hypocalcaemia

Trousseau’s sign

Inflation of BP cuff for several minutes induces carpopedal spasm = neuromuscular irritability due to hypocalcaemia

41
Q

What surgical process can lead to a risk of low Ca2+?

A

Parathyroid surgery

42
Q

What is low PTH levels called?

A

hypoparathyroidism

43
Q

What are the causes of hypocalcaemia?

A

Hypoparathyroidism
- surgical- neck surgery
- auto-immune
- magnesium deficiency
- congenital (agenesis, rare)

Vitamin D deficiency

44
Q

What are causes of vitamin D deficiency?

A

Malabsorption or dietary insufficiency
Inadequate sun exposure
Liver disease
Renal disease
Vitamin D receptor defects (rare)

45
Q

What stimulates renal 1-alpha-hydroxylase?

A

PTH

46
Q

What are the consequences of vitamin D deficiency?

A

Lack of bone mineralisation= soft bones

47
Q

What is vitamin D deficiency lead to in children and adults?

A

children= rickets (bowing of bones)

adults= osteomalacia (fractures, proximal myopathy (muscle weakness of upper/ lower limbs))

48
Q

What are the signs and symptoms of hypercalcaemia?

A

‘Stones, abdominal moans and psychic groans’
- Reduced neuronal excitability – atonal muscles

Stones – renal effects
Nephrocalcinosis – kidney stones, renal colic

Abdominal moans - GI effects
Anorexia, nausea, dyspepsia, constipation, pancreatitis

Psychic groans - CNS effects
Fatigue, depression, impaired concentration, altered mentation, coma (usually >3 mmol/L)

49
Q

What are causes of hypercalcaemia?

A

Primary hyperparathyroidism:
Too much PTH
Usually due to a parathyroid gland adenoma
No negative feedback - high PTH, but high calcium

Malignancy:
Bony metastases produce local factors to activate osteoclasts, increasing calcium reabsorption from bone

Vitamin D excess (rare)

50
Q

What is the hormonal control of phosphate regulated by?

A

FGF23
Vitmain D
PTH

BRS Endocrinology (12 decks)

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