Brainscape's Knowledge GenomeTM

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


See full index

DiBart 2021 > Chapter 6: Calcium > Flashcards

Chapter 6: Calcium Flashcards

1
Q

What are the major players in the Ca homeostatic control, and which controls the short-term vs long-term hemostasis?

A

PTH –> minute-to-minute control of serum [Ca]

Calcitriol (VitD) –> day-to-day control of serum [Ca]

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

How much of the Ca in the glomerular filtrate is reabsorbed by the tubular cells in a healthy animal?

A

almost all = 98%

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

How does the bone supply the body with Ca in the acute/short-term hypocalcemia?

A

Ca and P are mobilized from the bone ECF.

This ECF for fast Ca and P supply is separated from the rest of the bone via an osteoblast lining.

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

How does the bone supply the body with Ca in the chronic/long-term hypocalcemia?

A

osteoclastic bone resorption –> acids and proteases dissolute the mineralized bone matrix and by that mobilize Ca and P

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

How does decreased serum [iCa] affect PTH levels?

A

increased PTH secretion, causes:

  • osteoclastic bone resorption
  • increased renal Ca reabsorption
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How does decreased serum [iCa] affect calcitriol levels?

A

increased calcitriol synthesis, causes:

  • increased intestinal Ca absorption
  • osteoclastic bone resorption
  • increased renal tubular Ca reabsorption
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What acts as the “calcium pool” and how much of it is readily available?

A

bones
< 1% is readily available in the ECF outside of the osteoblast layer –> rest as hydroxyapatite, which is poorly exchangeable

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

What are the 3 fractions of plasma Ca?

A
  • ionized Ca (53%) –> biologically active form
  • complexed Ca (e.g., bound to phosphorous) (10%)
  • protein bound (34%)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Where is more Ca, in the ICF or ECF?

A

ECF –> 10,000-fold less in ICF than ECF

important because this enables rapid diffusion of ECF to ICF

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

What is the main function of the Calcium ion sensing receptors (CaSR)?

A
  • regulate PTH production in the parathyroid chief cells, i.e., increased serum [iCa] –> decreased PTH production
  • kidneys: increased serum [iCa] –> decreased tubular reabsorption of iCa, iMg, NaCl
  • kidneys: increased serum [iCa] –> decreased water reabsorption in the collecting ducts –> further promotes Ca excretion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Where is PTH synthesized and secreted?

A

in the chief cells of the parathyroid gland

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

What is the half-life of PTH in the blood?

A

3-5 minutes

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

How is PTH secretion and synthesis regulated?

A
  • calcitriol –> inhibits PTH mRNA synthesis + stimulates CaSR
  • serum [iCa] –> high levels inhibit PTH synthesis; low levels promotes PTH synthesis (principal stimulus
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Explain the mechanism behind secondary hyperparathyroidism from chronic kidney disease

A
  • calcitriol is activated in the kidneys –> CKD –> less activation of calcitriol –> lack of negative feedback on PTH synthesis and secretion
  • low serum [iCa] –> increased PTH secretion
  • kidneys fail to excrete P –> high serum [P] –> inhibits calcitriol production and promotes PTH production
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How does serum [Ca] affect PTH synthesis and secretion and what type of curve would illustrate their relationship in a diagram?

A
  • within a narrow range of serum [tCa] –> small changes of [tCa] will cause large changes in [PTH], e.g., small increase in [tCa] –> steep drop in [PTH]
  • out of this narrow range: effects of [tCa] on [PTH] are minimal
  • relationship creates a sigmoid curve
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is FGF-23 and how does it affect PTH levels

A

phosphatonin fibroblast growth factor-23

  • phosphaturic –> decreases serum [P] –> decreases PTH secretion
  • directly inhibitory of PTH secretion
  • calcitriol induces FGF-23 production –> FGF-23 in turn inhibits calcitriol synthesis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How is PTH metabolized?

A

Intact PTH can be taken up by fixed macrophages (e.g. Kupffer cells) and degraded into fragmented PTH. This process can also happen in bones and kidneys. Fragments of PTH are then filtered by glomeruli.

18
Q

Where is the calcitriol synthesis in the kidney?

A

Renal epithelial cells in the proximal convoluted tubules

19
Q

What are the biological effect of PTH on calcium?

A
  1. Increased the blood calcium concentration
  2. increase the renal tubular reabsorption of calcium -> decreased calcium loss in the urine
  3. increase bone resorption and the numbers of osteoclasts on bone surfaces
  4. induce synthesis of and activate the 1-𝜶hydroxylase in mitochondria of renal epithelial cells -> accelerate the formation of active vitamin D metabolite (1,25-dihydroxyvitamin D; calcitriol)
20
Q

Describe how does the bone respond to PTH

A

Biphasic
Immediate effect: an increased flow of calcium from deep in bone to bone surfaces through the action of an osteocyte-osteoblast “pump”
Later effect: osteoclast causing bone resorption and remodeling

21
Q

In which segments of the nephrons do PTH work on?

A

A direct action on the distal convoluted tubule
An indirect action on the ascending thick limb of Henle’s loop by increasing the net positive charge in the nephron lumen and creating a stimulus for diffusion out of the lumen.

22
Q

There are two terminals of PTH. Which one is important for calcium regulation?

A

N-terminal (amino acid 1-34)

23
Q

Does PTHrP participate in the normal regulation of calcium?

A

Yes. In fetus, PTHrP is produced by placenta and also secreted by fetal parathyroid chief cells, and is involved in the normal regulation of calcium.
PTHrP is also produced by the lactating mammary gland and is secreted into milk. It is thought to facilitates the movement of calcium from the maternal bones to the milk during lactation

24
Q

What are the relationship of cholecalciferol, calcidiol and calcitriol? Which one of above is the major circulating vitamin D?

A

Will put pic later

25-hydroxyvitamin D (calcidiol) (produced in liver)

25
Q

True or False: If you diagnose a dog with Vitamin D deficiency, besides vitamin D supplementation, it’s also recommended to sunbathe this dog more often since ultraviolet light help with vitamin D synthesis.

A

False. Dogs and cats inefficiently photosynthesize vitamin D in their skin.

26
Q

Where do the inactive vitamin D catabolites go?

A

Excreted through bile into feces, less than 4% is excreted through the urine

27
Q

What are the factors that stimulate calcitriol synthesis?

A

Hypocalcemia, calcitonin -> directly stimulate 1a-hydroxylation independent of PTH
Estrogen, testosterone

28
Q

What are the factors that inhibit calcitriol synthesis?

A

calcitriol, hypercalcemia, FGF-23, and phosphate loading

29
Q

True of False: Calcitriol increase both serum calcium and phosphorus concentrations through small intestine.

A

True :)

30
Q

What are other function of calcitriol?

A

up-regulation of calcitriol receptors in patients with uremia,
regulation of PTH synthesis and secretion by the parathyroid gland
prevention or reversal of parathyroid gland hyperplasia in the uremic patient

31
Q

How can we differentiate hypercalcemia as a cause or as a consequence of chronic renal failure?

A

By measuring iCa. Serum iCa is usually normal or low in patients with chronic renal failure, but increased in primary hyperparathyroidism.

32
Q

Why do we see serum total hypercalcemia and normal iCa concentrations in dogs with CKD?

A

The increased serum tCa is caused by an increase in the complexed calcium fraction. In CKD, organic anions such as citrates, phosphates, lactates, bicarbonates, and oxalates are capable of complexing with calcium.

33
Q

What is tertiary hyperparathyroidism?

A

Refers to the condition of a subset of patients with CKD who develop ionized hypercalcemia and excessive PTH secretion that is not inhibited by high serum iCa concentration. It is thought to be secondary to an alteration of the set-point for PTH secretion in patients with CKD due to the effects of uremic toxins, such that higher concentrations of iCa are necessary to inhibit PTH secretion.
Uremic toxins may decrease serum calcitriol concentrations, decrease the number of calcitriol receptors in the parathyroid gland, and decrease calcitriol-VDR interactions with chief cell DNA.

34
Q

True or false: Parathyroid gland masses cannot usually be palpated in both dogs and cats.

A

False. One report showed 50% of cats had a palpable cervical mass.

35
Q

True or false: Calcium urolithiasis is common in conditions causing hypercalcemia.

A

False. Most causes of hypercalcemia do not consistently cause calcium urolithiasis, but calcium urolithiasis is relatively common (present in ~30% of cases of dogs and cats) in primary hyperparathyroidism.

36
Q

True or false: Scintigraphy and ultrasound are equal in their specificity and sensitivity for parathyroid masses.

A

False. Scintigraphy appears to have rather low sensitivity and specificity whereas ultrasound (when performed with a 10-MHZ linear transducer) correctly identified the presence and location of parathyroid masses in 10/11 dogs in one study.

37
Q

True or false: Hypercalcemia from hypervitaminosis D can take up to 24 hours to develop and azotemia can take up to 72 hours to develop.

A

True

38
Q

True or false: The half-life of cholecalciferol is 21 days in dogs.

A

False. The half-life of cholecalciferol is 29 days in experimental dogs.

39
Q

True or false: Calcipotriene is a vitamin D analog.

A

True. Calcipotriene is present in many anti-psoriasis creams for humans. Its affinity for vitamin D binding protein is much less than calcitriol, so more is free in the serum to bind to vitamin D receptors. This causes more rapid onset of hypercalcemia as well as a more rapid decrease in calcium levels after catabolism.

40
Q

True or false: Macrophages do not typically express 1-∝-hydroxylase acitivity.

A

False. Normal macrophages do express 1-∝-hydroxylase acitivity when stimulated by interferon or LPS. Macrophages in granulomatous disease can express this activity without stimulation.

41
Q

Name other, less common, causes of hypercalcemia.

A
  1. Acute kidney injury (more common as patient transitions from oliguria to polyuria)
  2. Skeletal lesions (bacterial, fungal, hepatozoonosis)
  3. Neonatal septicemia
  4. Hypothermia
  5. Dehydration
  6. Hypertrophic osteodystrophy
  7. Disuse osteoporosis
  8. Hyperthyroidism in cats
  9. Calcium ingestion (calcium carbonate rocks, antacids)
  10. Grape/raisin ingestion
  11. Retained fetus and endometritis

DiBart 2021 (9 decks)

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