HORMONAL REGULATION OF CALCIUM AND PHOSPHATE METABOLISM

Question 1

in biological systems, __________ consists of a mixture of dihydrogen phosphate and hydrogen phosphate

Answer 1

inorganic phosphate

Question 2

two primary sources of circulating Ca and Pi are the diet and the skeleton, two hormones ______- and ___________ regulate intestinal absorption of calcium and phosphate and release of calcium and phosphate into the circulation after bone resorption

Answer 2

1,25 dihydroxyvitamin D
parathyroid hormone

Question 3

the ionized form of calcium represents about _____ of circulating calcium

Answer 3

50% of circulating calcium

Question 4

hypocalcemia is total serum calcium less than ____

Answer 4

less than 8.7

Question 5

hypercalcemia is total serum calcum more than _____

Answer 5

more than10.4

Question 6

because soft tissues contain 10-fold more phosphate than calcium, tissue damage can result in _________- wherein the increased phosphate complexes with calcium causes ________

Answer 6

hyperphosphatemia
acute hypocalcemia

Question 7

the predominant parenchymal cell type in the parathyroid gland is the _____________-

Answer 7

principal cell/chief cell

Question 8

PTH is secreted as an 84 amino acid polypeptide and is synthesized as _____ which is proteolytically processed ______ in the endoplasmic reticulum and then to PTH in the Golgi apparatus

Answer 8

Prepro-PTH
pro PTH

Question 9

PTH has a short half life in the circulation (___ minutes)

Answer 9

2 minutes

Question 10

becauses the PTH receptor also binds PTH related peptide (PTHrP), it is usually referred to as the ______________

Answer 10

PTH/PTHrP receptor

Question 11

_____ is a prohormone that must undergo two successive hydroxylation reactions to become the active form known as 1,25 dihydroxyvitamin D or ________

Answer 11

vitamin D
calcitriol

Question 12

hydroxylation at the 1 alpha position generates ______-, the most active form of vitamin D

Answer 12

1,25 dihydroxycholecalciferol

Question 13

vitamin d and its metabolites circulate in blood primarily bound to ____________ (DBP)

Answer 13

vitamin D binding protein

Question 14

the VDR is a ligand-dependent transcription factor that binds to cognate DNA sequences as a heterodimer with the ______-

Answer 14

retinoid X receptor

Question 15

movement of calcium from the gastrointestinal lumen into the enterocyte which is driven by both chemical and electrical gradients occurs via apical calcium channels called _____ and _____

Answer 15

TRPV5 and TRPV6

Question 16

once inside the cell, calcium ions bind to _______ which maintains a low cytoplasmic (Ca+) preserving the favorable transluminal membrane calcium gradient

Answer 16

calbindin-D

Question 17

the fraction of dietary phosphate is absorbed by the jejunum remains relative constant at about ______

Answer 17

70%

Question 18

the limiting process in transcellular Pi absorption is transport across the apical brush border which is mediated by the __________________ (NPT2)

Answer 18

sodium/phosphate cotransporter

Question 19

cells that form bone (____) and cells that destroy or resorb bone (____) osteoclasts

Answer 19

osteoblasts
osteoclasts

Question 20

osteoblasts release monocyte colony stimulating factor which expands and differentiates early hematopoietic progenitors into preosteoclasts that express a cell surface receptor called _______

Answer 20

RANK (receptor activator nuclear factor)

Question 21

osteoblasts-lineage cells can also produce a soluble factor called _____ which acts a s a decoy receptor for RANKL and inhibits osteoclast differentiation and function

Answer 21

osteoprotegerin

Question 22

as the osteoblasts become surrounded by and entrapped within the bone, they become _________ that sit within small spaces called the lacunae

Answer 22

osteocytes

Question 23

__________- binds to a receptor complex in proximal tubule cells and like PTH inhibits NPT2 to promote phosphate excretion

Answer 23

FGF23

Question 24

_______— promotes survival of osteoblasts and apoptosis of osteoclasts thereby favoring bone formation over resorption, for this reason women are susceptible to postmenopausal osteoporosis

Answer 24

estrogen