Vitamin D: Absorption, Transport, Metabolism, Storage

25-OH-D3 is hydroxylated in the kidney, it forms:

1, 25-OH2-D3 - Calcitriol

What enzyme made in the liver converts vitamin D3 to calcidiol (25-OH-D3)?

25 hydroxylase

In the liver, vitamin D3 (from diet and sun) is hydroxylated to:

25-OH-D3 / calcidiol

Storage form of vitamin D

25-OH-D3 / calcidiol

About _____% of dietary vitamin D is absorbed

50%

Metabolism overview: skin

7-dehydrocholesterol -> previtamin D3 -> vitamin D3

Metabolism overview: Kidney

Calcidiol -> calcitriol OR 24,25-OH2-D3 (vitamins degradation)

After hepatic synthesis, most 25-OH-D3 is secreted from the liver to the blood transported by:

VDBP and albumin

Metabolism overview: Liver

Vitamin D3 -> calcidiol

The main storage site or vitamin D =

adipose tissue

Main active form of vitamin D

calcitriol - 1,25-OH2-D3

Vitamin D is incorporated into _____________ for transport through lymph into circulation

chylomicron

simultaneous absorption with ____________ improves absorption

dietary lipids

Largest about of vitamin D is absorbed in the:

jejunum

2nd hydroxylation of vitamin D occurs in the:

kidney

1st hydroxylation of vitamin D occurs in the:

liver

Chylomicron remnants deliver dietary vitamin D not taken by tissues to

liver

Other tissues can convert vitamin D3 into 25-OH-D3 but the _________ is the main and most efficient site where this occurs

liver

Does dietary vitamin D (both D3 and D2) require digestion?

no

Chylomicrons transport dietary vitamin D to ___________________ throughout the body

nonhepatic tissues

Metabolism by the kidney is stimulated by:

parathyroid hormone (PTH)

Vitamin D is incorporated into micelle that diffuses through the lumen and unstirred water layer adjacent to the enterocytes enabling close contact with the brush border membrane. From this site, vitamin D is absorbed through:

passive diffusion into the enterocyte

The main pool of vitamin D =

the blood

VDBP =

vitamin D binding protein

Vitamin D3 made by the skin is picked up for transport in the blood by a:

vitamin D binding protein - VDBP

Concentrations of 25-OH-D3 reflects:

vitamin D status (diet and sun)

Cholecalciferol

vitamin D3

Vitamin D has a half-life of:

~3 weeks