Understanding Nutrition, 8e

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Understanding Nutrition, 8e

• Chapter 11 - The Fat-Soluble Vitamins A, D, E,
  and K

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Forms of Vitamin A
In this diagram, corners represent carbon atoms,
as in all previous diagrams in this book. A
further simplification here is that methyl groups
(CH3) are understood to be at the ends of the
lines extending from corners. (See Appendix C for
complete structures.)
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Conversion of Vitamin A Compounds
Notice that the conversion from retinol to
retinal is reversible, whereas the pathway from
retinal to retinoic acid is not.
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Vitamin As Role in Vision 1 of 3
As light enters the eye, pigments within the
cells of the retina absorb the light.
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Vitamin As Role in Vision 2 of 3
Each pigment molecule (in this diagram,
rhodopsin) contains retinal (an active form of
vitamin A) and a protein (in this diagram, opsin).
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Vitamin As Role in Vision 3 of 3
When rhodopsin absorbs light, its shape and color
change, generating nerve impulses that travel
into the brain.
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Mucous Membrane Integrity
Vitamin A maintains healthy cells in the mucous
membranes. Without vitamin A, the normal
structure and function of the cells in the mucous
membranes are impaired.
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Vitamin A Deficiency and Toxicity
As the dose increases from zero, normalcy is
reached. Intakes are safe over a wide range, and
then toxicity is reached.
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Food Sources of ?-Carotene
The carotenoids bring colors to meals the
retinoids allow us to see them.
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Vitamin D Synthesis and Activation
The precursor of vitamin D is made in the liver
from cholesterol (see Figure 5-10 on p. 134 and
Appendix C). The hydroxylation of vitamin D to
its active form is a closely regulated process.
The final product, active vitamin D, is
1,25-dihydroxycholecalciferol (or calcitriol).
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Vitamin DDeficiency Symptom
This child has the bowed legs commonly seen in
rickets.
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Vitamin D in Summary
Fontanel.
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Blood-Clotting Process
When blood is exposed to air, foreign substances,
or secretions from injured tissues, platelets
(small, cell-like structures in the blood)
release a phospholipid known as thromboplastin.
Thromboplastin catalyzes the conversion of the
inactive protein prothrombin to the active enzyme
thrombin. Thrombin then catalyzes the conversion
of the precursor protein fibrinogen to the active
protein fibrin that forms the clot.
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Food Sources of Vitamin K
Notable food sources of vitamin K include milk,
eggs, brussels sprouts, liver, cabbage, spinach,
and broccoli. Thromboplastin catalyzes the
conversion of the inactive protein prothrombin to
the active enzyme thrombin. Thrombin then
catalyzes the conversion of the precursor protein
fibrinogen to the active protein fibrin that
forms the clot.
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Cruciferous Vegetables
Cruciferous vegetables, such as cauliflower,
broccoli, and brussels sprouts, contain nutrients
and nonnutrients that may inhibit cancer
development. Thromboplastin catalyzes the
conversion of the inactive protein prothrombin to
the active enzyme thrombin. Thrombin then
catalyzes the conversion of the precursor protein
fibrinogen to the active protein fibrin that
forms the clot.
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