Brainscape's Knowledge GenomeTM

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


See full index

RDA > Lecture 9 + 10 - 2018/2017 > Flashcards

Lecture 9 + 10 - 2018/2017 Flashcards

1
Q

What is PTH?

A

Parathyroid hormone.

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

What makes PTH?

A

Chief cells of parathyroid gland.

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

Why is PTH made?

A

In response to low calcium levels in serum (ECF - blood).

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

How does PTH restore calcium levels back to normal?

A
  1. Stimulation of renal tubular reabsorption of calcium - rapid action.
  2. Stimulates osteoclastic bone resorption - there is an increase in osteoclasts, so there is an increase in bone being broken down and consequently calcium is released in the blood (intermediate action).
  3. Stimulates renal 1-hydroxylation of 25(OH)D - there is stimulation on the intestine to promote calcium absorption cia 1-hydroxylation of 25()H)D -> 1,23 (OH)2D.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is PTH regulated by?

A
  1. Serum ionised calcium.
  2. Serum phosphate.
  3. Serum 1,25 Dihdroxy vitamin D.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How does calcium regulate PTH?

A

If we increase calcium then there will be a decrease in PTH. This acts as a negative feedback.

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

How does phosphate regulate PTH?

A

If we increase phosphate there will be an increase in PTH.

N.B. PTH will cause a decrease in absorption of phosphate via the kidney.

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

How does 1,25 Dihydroxy Vitamin D regulate PTH?

A

If we increase 1,25 dihydroxy vitamin D there will be a decrease in PTH.

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

What is CaR?

A

It is a specific calcium receptor at the parathyroid gland - sits at the membrane of the cell and binds to calcium.

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

What happens when there is a decrease in calcium?

A

The lack of calcium means that there is no calcium bound to the receptors. The CaR will then activate a gene transcription for production of PTH. PTH is then released into the ECF.

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

What happens when there is an increase in calcium?

A

Calcium binds to CaR on the ECF side of the renal tubule - CaR activates processes which switch of reabsorption of calcium from the urine.

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

What is PTHrP?

A

Parathryoid Horomone-Related Peptide.

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

What does PTHrP do?

A

Paracrine regulator of bone and breast development - it is NOT a physiological regulator of serum calcium. it acts like PTH and cause an increase in calcium.

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

What produces PTHrP?

A

It is produced in excess by neoplasms especially those derived from epithelial tissues e.g. humoral hypercalcemiia of malignancy (HHM).

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

What does PTHrP do in bone?

A

Stimulates calcium release.

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

What does PTHrP do in kidney?

A
  1. Increases renal tubular reabsorption of calcium.

2. Decreases renal tubular reabsorption of phosphate - lowers plasma phosphate.

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

What are the signs of PTH dependent hypercalcemia?

A
  1. Increase in calcium.

2. Increase in PTH (inappropriately normal).

18
Q

What causes PTH dependent hypercalcemia?

A
  1. Primary hyperparathyroidism - 85% solitary adenoma, 10-15% parathyroid gland hyperplasia.
  2. Familial benign hypercalcemia (FHH/FBH) - there is inactivating CaSR mutations (calcium sensing receptors - basically the receptors are inactive and sense less calcium then there really is, this means that PTH detects this and will make more calcium hence hypercalcemia).
19
Q

What are the signs of PTH independent hypercalcemia?

A
  1. Increase in calcium.

2. Decrease in PTH.

20
Q

What causes PTH independent hypercalcemia?

A
  1. Cancer.

2. Vitamin D toxicity.

21
Q

How does cancer cause PTH independent hypercalcemia?

A
  1. Tumours secrete PTHrP.
  2. Extensive lytic bone disease (bone resorption) e.g. multiple myeloma (bone marrow malignancy) - increase in breakdown of bone so increase in calcium.
  3. Tumour expression of 1-alpha hydroxylase which leads to an increase in 1,25 (OH)2D.
22
Q

How does vitamin d toxicity cause PTH independent hypercalcemia?

A
  1. Endogenous - granulomatous disease (sarcoidosis).

2. Exogenous - iatrogenic (vitamin d intoxication).

23
Q

What are the causes of hypocalcemia?

A
  1. Hypoparathyroidism.
  2. Parathyroid hormone resistance.
  3. Abnormalities of vitamin D metabolism.
24
Q

How does hypoparathyroidism cause hypocalcemia?

A
  1. Post surgical e.g. post neck irradiation.
  2. Genetic e.g. CaSR mutations - receptor is always active (the parathyroid is told that there is an increase in calcium than there really is, so there is a decrease in PTH so there is a decrease in calcium).
  3. Severe hypomagnesaemia.
  4. Autoimmune.
  5. Infiltrative e.g. beta-thalassaemia, wilson’s disease.
25
Q

How does parathyroid hormone resistance cause hypocalcemia?

A
  1. Pseudohypoparathyroidism (types 1a, 1b, 1c).
26
Q

How does abnormalities of vitamin d metabolism cause hypocalcemia?

A
  1. Vitamin D deficiency - can’t make enough 1,25 Vit D thus decrease in calcium absorption in gut.
  2. Deficient in 1-alpha hydroxylation - can’t convert vitamin D.
  3. Renal failure.
  4. Vitamin D resistance.
27
Q

What is autosomal dominant hypercalciuric hypocalcemia?

A

The CaSR sense more calcium than there really is so there is a decrease in PTH so there will be a decrease in calcium.

28
Q

What are the features of autosomal dominant hypercalciuric hypocalcemia?

A
  1. Autosomal dominant inheritance.
  2. Hypocalcemia - usually asymptomatic.
  3. Mild hypomagnesemia (0.5-0.7).
  4. Higher urinary calcium excretion - this is because the CaR regulates renal tubular calcium handling therefore it tells the cells to not reabsorb calcium into the blood therefore calciums tays in the urine hence increase in urine calcium.
29
Q

What is familial hypocalciuric hypercalcemia (FHH)?

A

The CaSR sense less calcium than there really is so there is an increase in PTH so there will be an increase in calcium.

30
Q

How do you diagnose FHH?

A
  1. Screening immediate relatives (AD inheritance).
  2. Ratio of fasting urine calcium to creatinine clearance.
  3. Family testing (serum calcium).
31
Q

Where is phosphate found?

A
  1. Cell membranes.
  2. Intracellular organelles.
  3. Nucleic acids.
  4. Enzyme co-factors and glycolytic intermediates.
32
Q

What regulates phosphate metabolism?

A
  1. PTH.

2. Calcitriol.

33
Q

How does PTH regulate phosphate levels?

A

It decreases serum phosphate.

34
Q

How does calcitriol regulate phosphate levels?

A

It increases serum phosphate by increasing intestinal absorption of phosphate and decreasing urinary phosphate excretion.

35
Q

What effect does phosphate have on PTH?

A

Low levels of phosphate will inhibit PTH production and increase calcitriol production.

36
Q

What are phosphatonins?

A

Family of hormones that regulate serum phosphate levels by modulating the expression of phosphate-transporting proteins in the renal tubule and thereby urinary phosphate excretion.

37
Q

Where do phosphatonins come from?

A

The main source is the skeleton, specifically osteoblasts and osteocytes.

38
Q

What is FGF23?

A

It is a phosphatonin that is the main regulator of phosphate.

39
Q

How does FGF23 regulate phosphate?

A

When there is an increase in phosphate, FGF23 (phosphatonin) is released from the bone. It acts on:
1. The kidney (reduce NaPi-2a,2c) to reduce phosphate reabsorption.
2. The gut (reduce 1,25 (OH)2D) to reduce phosphate reabsorption.
By doing the above FGF23 will cause there to be a decrease in serum phosphate levels.

40
Q

What causes hyperphosphatemia?

A
  1. Increased input of phosphate - IV phosphate, cell death.
  2. Decreased excretion of phosphate - renal failure, PTH deficiency or resistance.
41
Q

What causes hypophosphatemia?

A
  1. Inadequate GI absorption - vitamin d deficiency.
  2. Intracellular shift - acute flux of phosphate from extracellular space to intracellular.
  3. Renal loss - increase in PTH (PTH producing adenoma) or increase in phosphatonins.
42
Q

What causes an intracellular shift in phosphate (which can cause hypophosphatemia)?

A
  1. Respiratory alkalosis - illness, pain (usually self-limiting).
  2. Prolonged intense exercise.
  3. Re-feeding malnourished patients.

RDA (19 decks)

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