Calcium Homeostasis Flashcards
How is vit D2 and D3 (key factors in regulation of calcium homeostasis) produced?
In specific, vit D2 is produced from the plant?
Another name for vit D2 is?
Another name for vit D3 is?
Metabolism of Vit D yields the active metab. That plays a crucial role in?
What are dietary sources?
Produced from steroids by UV irradiation
Sterol ergosterol
Ergocalciferol
Cholecalciferol
Calcium homeostasis
Animal origin (meat, dairy)
How does cholesterol become vit D3?
Cholesterol is converted to 7-dehydrocholesterol. When it is exposed to sunlight, the 6,7 cis double bond isomerizes to produce vit D3
What blood-born a-2 globulin binds to vit D3 in the blood?
Vitamin-D-binding protein (DBP) aka transcalciferin
***map out slide 3
Where is vit D3 from diet absorbed?
Vit D is packaged into ________ in its target cells
In the LIVER, and lungs, kidney, and intestine, cholecalciferol is converted to _______________ by the enzyme ___________.
Small intestine
Chylomicrons
25-hydroxycholecalciferol (25-OH D3), 25-hydroxylase via P450
25-OH D3 bound to DBP is taken up by the ______ and undergoes hydroxylation at position 1 to form ____________ which is mediated by the enzyme _________. This enzymes activity is stimulated by ____________ and by low plasma ______ and ________.
Kidneys
1,25-dihydroxycholecalciferol (calcitriol), 1-hydroxylase
Parathyroid hormone, calcium, phosphorus
Overproduction of 1,25-(OH)2 D3 leads to inactivation by __________ of ____________ or _________
24-hydroxylation, 1,25-(OH)2 D3, 25-OH D3
Target tissues take up DBP bound 1,25-(OH)2 D3 which then binds to a ____________. This triggers intracellular signaling which has nongenomic effects of increased _______________ in the intestine or increased _______________ in other tissues
Vitamin D receptor (VDR)
Calcium absorption, trans cellular calcium flux
Genomic effects of 1,25-(OH)2: complex is transported to the nucleus to form a heterodimer with ______. The ________ complex has high affinity for vitamin D response element. Target genes then code for proteins involved in ____________, which include _______, _______, __________, and certain calcium channel proteins
RXR
RXR-VDR
Calcium homeostasis, osteocalcin, calbindin, 24-hydroxylase
In bone tissue, PTH + 1,25-(OH)2 D3 increases blood ______ and _______ concentrations by stimulating bone resorption in _______ to dissolve bone tissue. When _____ blood levels are too high, _____ is released from thyroid glands to promote ____________.
Calcium, phosphorus, osteoclasts
Calcium, calcitonin, bone mineralization
** diagram pg 6
Other roles of vit D:
Induces cell differentiation of stem cell monocytes in bone marrow to become ____________.
Stimulates skin epidermal cell __________ and prevents cell ____________ which makes it a possible treatment of _______
May be used in the treatment of _____ diseases , hyper___________, and skin ______
Also plays a role in prevention of ______________ and down-regulate __________ mediators and increase ___________ sensitivity.
Mature osteoclasts
Differentiation, proliferation, psoriasis
Bone, parathyroidism, cancer
Autoimmune disorders, inflammatory, insulin
Metabolism and excretion:
1,25-(OH)2 D is converted into the less active _________ which may be oxidized to the ________ metabolite or undergo __________ cleavage.
These metabolites may be ___________ and primarily excreted in the ____.
1,24,25-(OH)3 D, 24-oxo, side-chain
Glucuronidated, bile
Recommended dietary allowance of vit D:
Adult men and women under 70?
Over 71?
Pregnancy and lactation?
Exposure to sunlight for 5-15 min can produce _____ vitamin D
15 ug (600IU)/day
20 ug (800IU)/day
15 ug (600IU)/day
25 ug (100IU)
What is a disease state caused by vit D deficiency in infants and children? SEs?
Why are breast-fed children potentially at risk?
Rickets
Seizures, growth retardation, impaired bone mineralization
Human milk is low in vit D, esp. if minimally exposed to sunlight
