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Endo > Physiology 1: Calcium And Phosphate Hemeostasis > Flashcards

Physiology 1: Calcium And Phosphate Hemeostasis Flashcards

1
Q

What is the most abundant cation in the body?

A

Calcium.

(Calcium - Cation).

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2
Q

Where is 99% of calcium present?

A

Bones and teeth.

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3
Q

What is the form of Calcium present in bones and teeth?

A

Present as the mineral Hydroxyapatite, Ca10(PO4)6(OH)2.

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4
Q

Calcium regulation involves which three tissues and three hormones?

A

Three tissues: bone, intestine, kidney.
Three hormones: PTH, calcitonin, activated vitamin D3.

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5
Q

Where is organic phosphate compounds present?

A

In the structural units of cell.

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6
Q

What is inorganic phosphate associated with?

A

Calcium in the bone and teeth.

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7
Q

What plays an important role in regulating neutrality?

A

Calcium and serum phosphate.
And it is in equilibrium with both bone and cellular organic phosphates.

(Ca+, Phosphate-).

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8
Q

Blood level is held relatively constant by what?

A

By regulating phosphate excretion by the kidney.

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9
Q

The control of blood level is primarily mediated by action of what?

A

Parathyroid hormone.

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10
Q

What enhances entry of phosphate into bone?

A

Vitamin D.

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11
Q

Which clotting factor is NOT made in the liver?

A

Ca (clotting factor 4).

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12
Q

List the 11 functions of calcium?

A

1- Structural integrity and metabolism of bone (bone growth and remodeling).
2-Tooth formation.
3- Coenzyme function - e.g. in hemostatic (clotting cascade).
4- Synaptic transmission.
5- Stimulus - secretion coupling: in nerve terminals; endocrine and exocrine glands (exocytosis)*.
6- Excitation - contraction coupling: in muscles.
7- Control of excitability of nerve and muscle cells: stabilization of membrane potentials by modulation of permeability to sodium and potassium.
8- Regulation of transmembrane ion transport.
9- Second messenger in intracellular signal transduction pathways.
10- Cell motility.
11- Gene expression.

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13
Q

List the 3 different forms of calcium in plasma?

A

1- Ionized (free) form (the physiologically active form).
2- Bound to proteins (predominantly albumin).
3- Complexed with anions (citrate, sulfate, phosphate).

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14
Q

Which form of calcium does the previous functions of calcium?

A

The ionized form.

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15
Q

What is the percentage of the ionized form of calcium in plasma?

A

45-50%.

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16
Q

What is the percentage of calcium that is bound to proteins in plasma?

A

40%.

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17
Q

What is the percentage of calcium that is complexed with anions in plasma?

A

10-15%.

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18
Q

What is the equation for Serum Calcium (Total)?

A

Serum Calcium (Total) = (Free) calcium + (Bound) calcium to albumin.

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19
Q

The routine laboratory investigations show which type of calcium?

A

The serum calcium (total).

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20
Q

In clinical conditions where there is low levels of albumin, the total calcium will be reported as what?

A

Falsely low.
(Because there aren’t any albumin for Ca to bind to, but it is not actually low).

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21
Q

To get the correct calcium level in states of hypoalbuminemia we use which formula?

A

[Ca+2] Corrected = [Ca+2] Measured + [0.8 (4 - Albumin)].

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22
Q

List the 3 calcium regulatory mechanisms?

A

1- Intestinal absorption (vitamin D dependent): duodenum and proximal jejunum.
2- Renal tubular reabsorption and excretion.
3- Exchange of calcium between plasma and bone: bone remodeling.

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23
Q

Plasma calcium homeostasis depends on what?

A

Balance between the hypocalcamic effects of calcitonin and the hypercalcamic effects of PTH, vitamin D and calcium intake.

24
Q

What is the location of calcium absorption in the body? And by which mechanism?

A

Absorbed in the small intestine, by both active transport and by diffusion.

25
Q

What regulates the amount of cytosolic calcium-binding protein and activates the active transport systems?

A

Vitamin D (1,25 dihydroxyvitamin D3 - calcitriol).

26
Q

What indirectly increases small intestinal absorption and by enhancing which activity?

A

Parathyroid hormone,
By enhancing 1-alpha-hydroxalase activity and calcitriol synthesis.

27
Q

What is the percentage of renal excretion of ingested calcium?

A

10%.

28
Q

Which type of calcium is not filtered (not excreted by renal)?

A

Calcium bound to plasma proteins.

29
Q

Which type of calcium is filtered in the glomerulus?

A

Ionized and complex form.

30
Q

Which part of the kidney reabsorbs 70% of filtered calcium?

A

Proximal tubule.

31
Q

Which part of the kidney reabsorbs 20% of filtered calcium?

A

Loop of Henle.

32
Q

Which part of the kidney reabsorbs 9% of filtered calcium?

A

Distal tubule.

33
Q

What detects the serum calcium concentration, and determines the serum PTH concentration?

A

Calcium-sensing receptor (CaSR) on parathyroid cells.

34
Q

______ calcium levels stimulate PTH secretion.
______ calcium levels inhibit PTH secretion.

A

LOW calcium levels stimulate PTH secretions,
HIGH calcium levels inhibit PTH secretions.

35
Q

Which mineral is required for PTH release and for its effects on target tissues?

A

Magnesium.

36
Q

Disorders of magnesium metabolism may manifest as what?

A

Hyper- or Hypo- parathyroidism.

37
Q

What are the 4 actions of PTH on bones?

A

1- Liberates calcium from bone.
2- Bone resorptive effect.
3- Stimulates osteoclasts*.
4- Transports calcium from bone to ECF.

38
Q

What are the 3 actions of PTH on the GIT?

A

1- Uptake calcium.
2- Increased absorption of phosphate.
3- Indirect action - through vitamin D *.

39
Q

What are the 4 actions of PTH on the kidney?

A

1- Increased reabsorption of calcium *.
2- Reabsorption in late distal tubules, the collection tubules, the early collecting ducts, ascending loop of Henle.
3- Increased urinary excretion of phosphate *.
4- Stimulates renal hydroxylation of 25-hydroxy vitamin D3 to 1,25-dihydroxyvitamin D3 [increased 1-alpha- hydroxalase activity] *.

40
Q

List the mechanism in which vitamin D is made?

A

1- Vitamin D3/cholecalciferol is formed in the skin, as a result of 7-dehydrocholesterol, by UV rays.

2- Cholecalciferol is converted to 25-hydroxycholecalciferol in the liver.

3- 25-hydroxycholecalciferol is converted to 1,25- Dihydroxycholecalciferol in the proximal tubule (conversion requires PTH).

41
Q

Why is PTH important in vitamin D synthesis?

A

PTH induces 1-alpha-hydroxylase activity in the kidney.

25-hydroxyvitamin D3 > 1,25-dihydroxyvitamin D3

(> = 1-alpha-hydroxylase)*.

42
Q

What are the 3 functions of vitamin D3?

A

1- Increases intestinal calcium and phosphate absorption.

2- Increases calcium and phosphate reabsorption in the kidneys *.

3- Increases calcium transporters through cellular membranes in bone - increases reabsorption.

43
Q

How does vitamin D3 increase intestinal calcium and phosphate absorption?

A

Induces a luminal membrane calcium channel and calcium-binding protein (Calbindin) in the cytosol *.

44
Q

How does vitamin D3 increases calcium and phosphate reabsorption in kidneys?

A

By inducing active calcium reabsorption in the DCT *.

45
Q

Where is Calcitonin secreted from? And what is its effects?

A

Secreted from parafollicular cells, or C cells, in the follicles of the thyroid gland.

It has the opposite effects of PTH (decreases plasma calcium concentration).

46
Q

How does calcitonin decrease plasma calcium concentration? (4 points).

A

1- Decrease the absorptive activities of the osteoclasts and the osteolytic effect in the bone.
2- Deposition of calcium in the bone salts.

3- Inhibits renal tubular cell reabsorption of Ca 2+, allowing it to be excreted in the urine - opposite to PTH *.

4- Inhibits phosphate reabsorption by the kidney tubules *.

47
Q

Effects of calcitonin is much greater in which age group and why?

A

Children, because bone remodeling occurs rapidly in children by bone absorption and deposition.

48
Q

List the 4 main causes of hypercalcemia?

A

1- Increased GI Absorption: *
- Elevated calcitriol.
- Vitamin D excess: *
- Excessive dietary intake.
- Granuomatous diseases.
- Elevated PTH.
- Hypophosphatemia.

2- Increased Loss From Bone: *
- Elevated PTH: Hyperparathyroidism *.
- Malignancy (PTHrP=PTH related peptide) *.
- Increased bone turnover:
- Paget’s disease of bone.
- Hyperthyroidism.

3- Decreased Bone Mineralization: *
- Elevated PTH.

4- Decreased Urinary Excretion: *
- Thiazide diuretics *.
- Elevated calcitriol.
- Elevated PTH.

49
Q

What are the 4 clinical manifestations of hypercalcemia?

A

1- Stones * (renal stones).
2- Bones * (osteitis fibrosa/arthritis).
3- Abdominal Groans * (constipation, nausea, vomiting, pancreatitis).
4- Psychic Moans * (lethargy, depression, memory loss, confusion, stupor, coma).

50
Q

What are the 3 causes of hypocalcemia?

A

1- Decreased GI Absorption: *
- Poor dietary intake of calcium *.
- Impaired absorption of calcium:
- Vitamin D deficiency.
- Liver failure, renal failure.
- Low PTH, hyperphosphatemia.

2- Decreased Bone Reabsorption/ Increased Mineralization: *
- Low PTH (hypoparathyrodisim)*.
- PTH resistance (pseudohypoparathyroidism).
- Vitamin D deficiency.
- Osteoblastic metastases.

3- Increased Urinary Excretion: *
- Low PTH (after thyroidectomy, after I131 treatment).
- autoimmune hypoparathyroidism.
- PTH resistance.
- Loop diuretics and biphosphonates *.
- Vitamin D deficiency/ low calcitriol.

51
Q

List the 5 clinical manifestations of hypocalcemia?

A

1- Increased neuromuscular excitability:
- Convulsions *.
- Paresthesia.
- Hyperreflexia *.
2- Cardiac effects:
- Arrhythmias *.
- Repolarization is delayed, with prolongation of the QT interval.
3- Tetany:
- Manifest- Carpopedal spasm .
- Latent- Trousseau’s sign and Chovestek’s sign.
4- Laryngeal stridor *.
5- Ophthalmological effects:
- Papilledema.
- Cataract.

(CATS).

52
Q

Why does respiratory alkalosis happen in cases of hypocalcemia?

A

The respiratory alkalosis causes increased binding of calcium to albumin, thus leading to a decreased free calcium.

53
Q

What is clinical manifestation of Vitamin D deficiency in children?

A

Rickets:
- failure of bones to grow properly.
- results in “bowed” legs, outward bowed chest and knobs on ribs.

54
Q

What are the clinical manifestations of Vitamin D deficiency in adults?

A

1- Osteomalacia: Adult form of rickets:
- Softening of bones, bending of spine, and bowing of legs.

2- Osteoporosis (porous bone):
- Vitamin D plays a major role along with calcium.
- Loss of vitamin D activity with advancing age.
- associated with fractures > very serious for geriatrics.

55
Q

What is the mechanism of osteoporosis vs. osteomalacia?

A

-Osteoporosis: bone loss.
-Osteomalacia: incomplete mineralization.

56
Q

List the common causes of osteoporosis vs. osteomalacia?

A

-Osteoporosis: Lack of sex hormones, old age, inactivity corticosteroid therapy.
-Osteomalacia: Vitamin D and/or calcium deficiency.

57
Q

List the main symptoms of osteoporosis vs. osteomalacia?

A

-Osteoporosis: none, until fracture or deformity occurs (late).
-Osteomalacia: generalized bone pain and deformity (early).

Endo (8 decks)

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