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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
What regulates the amount of cytosolic calcium-binding protein and activates the active transport systems?
Vitamin D (1,25 dihydroxyvitamin D3 - calcitriol).
26
What indirectly increases small intestinal absorption and by enhancing which activity?
Parathyroid hormone, By enhancing 1-alpha-hydroxalase activity and calcitriol synthesis.
27
What is the percentage of renal excretion of ingested calcium?
10%.
28
Which type of calcium is not filtered (not excreted by renal)?
Calcium bound to plasma proteins.
29
Which type of calcium is filtered in the glomerulus?
Ionized and complex form.
30
Which part of the kidney reabsorbs 70% of filtered calcium?
Proximal tubule.
31
Which part of the kidney reabsorbs 20% of filtered calcium?
Loop of Henle.
32
Which part of the kidney reabsorbs 9% of filtered calcium?
Distal tubule.
33
What detects the serum calcium concentration, and determines the serum PTH concentration?
Calcium-sensing receptor (CaSR) on parathyroid cells.
34
______ calcium levels stimulate PTH secretion. ______ calcium levels inhibit PTH secretion.
LOW calcium levels stimulate PTH secretions, HIGH calcium levels inhibit PTH secretions.
35
Which mineral is required for PTH release and for its effects on target tissues?
Magnesium.
36
Disorders of magnesium metabolism may manifest as what?
Hyper- or Hypo- parathyroidism.
37
What are the 4 actions of PTH on bones?
1- Liberates calcium from bone. 2- Bone resorptive effect. 3- Stimulates osteoclasts*. 4- Transports calcium from bone to ECF.
38
What are the 3 actions of PTH on the GIT?
1- Uptake calcium. 2- Increased absorption of phosphate. 3- Indirect action - through vitamin D *.
39
What are the 4 actions of PTH on the kidney?
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
List the mechanism in which vitamin D is made?
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
Why is PTH important in vitamin D synthesis?
PTH induces 1-alpha-hydroxylase activity in the kidney. 25-hydroxyvitamin D3 > 1,25-dihydroxyvitamin D3 (> = 1-alpha-hydroxylase)*.
42
What are the 3 functions of vitamin D3?
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
How does vitamin D3 increase intestinal calcium and phosphate absorption?
Induces a luminal membrane calcium channel and calcium-binding protein (Calbindin) in the cytosol *.
44
How does vitamin D3 increases calcium and phosphate reabsorption in kidneys?
By inducing active calcium reabsorption in the DCT *.
45
Where is Calcitonin secreted from? And what is its effects?
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
How does calcitonin decrease plasma calcium concentration? (4 points).
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
Effects of calcitonin is much greater in which age group and why?
Children, because bone remodeling occurs rapidly in children by bone absorption and deposition.
48
List the 4 main causes of hypercalcemia?
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
What are the 4 clinical manifestations of hypercalcemia?
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
What are the 3 causes of hypocalcemia?
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
List the 5 clinical manifestations of hypocalcemia?
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
Why does respiratory alkalosis happen in cases of hypocalcemia?
The respiratory alkalosis causes increased binding of calcium to albumin, thus leading to a decreased free calcium.
53
What is clinical manifestation of Vitamin D deficiency in children?
Rickets: - failure of bones to grow properly. - results in “bowed” legs, outward bowed chest and knobs on ribs.
54
What are the clinical manifestations of Vitamin D deficiency in adults?
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
What is the mechanism of osteoporosis vs. osteomalacia?
-Osteoporosis: bone loss. -Osteomalacia: incomplete mineralization.
56
List the common causes of osteoporosis vs. osteomalacia?
-Osteoporosis: Lack of sex hormones, old age, inactivity corticosteroid therapy. -Osteomalacia: Vitamin D and/or calcium deficiency.
57
List the main symptoms of osteoporosis vs. osteomalacia?
-Osteoporosis: none, until fracture or deformity occurs (late). -Osteomalacia: generalized bone pain and deformity (early).

Endo (8 decks)

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