Parathyroid, Calcitonin, Calcium, Phosphate, Vit D

Question 1

Normal ECF calcium concentration

Answer 1

9.4 mg/dl
or
2mmol/liter

Question 2

True or false: Calcium is important in blood clotting process

Answer 2

True

Question 3

Effect of hypercalcemia and hypocalcemia on nervous system.

Answer 3

Hypercalcemia makes sodium channels more resistant to opening potassium channels making it harder to initiate action potentials

Hypocalcemia makes cells more permeable to sodium, causing excess stimulation

Question 4

Percentages of phosphate versus calcium in different reservoirs

Answer 4

Bone is largest calcium reservoir (98.9%)
1% Calcium goes to cells, 0.1% in ECF

Bone is also largest phosphate reservoir (85%)
15% in cells and less than 1% in ECF

Question 5

Forms in which calcium exists in blood.

Answer 5

Ionized
Complexed to anions
Bound to plasma proteins

Question 6

Which forms of calcium are diffusable?

Answer 6

Ionized form and the one complexed to anions

Question 7

Greatest percent of calcium exists in which form?

Answer 7

Ionized (50%)

Question 8

relative concentrations of calcium in ICF and Intersitial fluid to plasma

Answer 8

1/2 that of total plasma
in ICF and insterstitial fluid it is 1.2mmol, but in plasma it’s about 2.4 since this calcium remains bound to plasma proteins and cannot diffuse

Question 9

Forms phosphate found in blood

Answer 9

H2PO4- and HPO4(with charge of 2-)

Question 10

Which form of phosphate found in greater quantity?

Answer 10

HPO4 (with charge of 2-) since body’s pH is slightly basic (7.4)

Question 11

Compare absorption and secretion of calcium and phosphate by GIT

Answer 11

90% of calcium is lost in feces only 10% is absorbed by GIT

Phosphate on the other hand is easily absorbed and most of it is not lost

Question 12

Amount of calcium excreted in feces? urine?

Answer 12

90% in feces, 10% in urine

Question 13

Renal tubules reabsorb how much calcium?

Answer 13

99% of the 10% Calcium lost in urine

Question 14

Part of kidney where most calcium reabsorption occurs

Answer 14

Glomerular filtrate
Early portion of collecting tubules
Loops of Henle
Proximal tubules

Question 15

Control of calcium secretion is by

Answer 15

PTH (Parathyroid hormone)

Question 16

PTH effect on calcium and phosphate absorption in kidneys

Answer 16

increases secretion of phosphate

promotes calcium absorption

Question 17

Explain overflow mechanism of phospate excretion

Answer 17

When phosphate is above critical level of 1 mmol/L, rate of its loss is directly proportional to rate of increase in its concentration

But when it’s below this critical level, ALL the phosphate is reabsorbed

Question 18

Most abundant glycoproteins in bone ground substance

Answer 18

Chondroitin sulfate and Hyaluronic acid

Question 19

Calcium to phosphorus ratio in bone matrix

Answer 19

ranges from 1.3 -2.0

Question 20

Tensile strength of bone due to ______ while compressional strength due to ________

Answer 20

Tensile strength of bone due to collagen while compressional strength due to crystals

Question 21

Arrangement of bone matrix to give it its strength

Answer 21

Crystals bind very strongly to collagen preventing them from slipping out of place. Also crystals overlap in brick-like manner adding to the bone’s strength and resistance

Question 22

Molecule preventing precipitation of hyroxyapatite crystals in soft tissues

Answer 22

Pyrophosphate

Question 23

Mechanism of bone calcification

Answer 23

Laying down of ground substance by osteoblasts. collagen monomers; form polypeptides to form collagen fibers. Also secretion of proteoglycans.

Osteoblasts get traped in own matrix and become osteocytes which are less active.

Nidi form as calcium precipitates not yet in the form of crystals bind to collagen.

Via addition and substution, nidi components crystallized, but some remain in amorphous state as a readily usable reservoir to correct any sudden calcium changes in plasma.