Understanding Nutrition, Chapter 11: The Fat-Soluble Vitamins: A, D, E, and K

Vocabulary flashcards covering the fat-soluble vitamins (A, D, E, and K), their active chemical forms, physiological roles, deficiency syndromes, metabolic pathways, and antioxidant mechanisms based on Chapter 11.

Beta-carotene

A plant-derived carotenoid and precursor of vitamin A that functions as an antioxidant and can be cleaved to yield vitamin A.

Retinoids

The group of chemically related compounds active as vitamin A in the body, consisting of retinol, retinal, and retinoic acid.

Retinol-Binding Protein (RBP)

A specific transport protein that picks up vitamin A from its storage site in the liver and carries it through the bloodstream.

Retinol

The alcohol form of vitamin A that supports reproduction and participates in a reversible interconversion with retinal in the body.

Retinal

The aldehyde form of vitamin A that participates in vision by combining with the protein opsin to form the visual pigment rhodopsin.

Retinoic Acid

The acid form of vitamin A formed irreversibly from retinal that functions in regulating cell differentiation, growth, and development.

Conversion of Vitamin A Compounds

The metabolic pathway where retinoids from animal foods yield retinol, carotenoids from plant foods yield retinal, retinol and retinal interconvert reversibly, and retinal converts irreversibly into retinoic acid.

Cornea

The transparent outer window at the front of the eye whose structural clarity is maintained by vitamin A.

Rhodopsin

The light-sensitive pigment found in retinal rod cells, composed of the protein opsin bound to cis-retinal, which isomerizes to trans-retinal when absorbing light energy to trigger a nerve impulse.

Goblet Cells

Single-celled glands situated within epithelial linings and mucous membranes that synthesize and secrete lubricating and protective mucus.

Night Blindness

One of the first detectable signs of vitamin A deficiency caused by inadequate retinal at the retina, characterized by an impaired ability to recover vision after exposure to bright light or see in dim light.

Xerophthalmia

Progressive blindness caused by severe vitamin A deficiency at the cornea, advancing from dry and thickened tissue (xerosis) to corneal softening and irreversible blindness (keratomalacia).

Keratinization

An abnormal process resulting from vitamin A deficiency where epithelial cells produce keratin, causing the skin to become dry, rough, and scaly while mucous membrane goblet cells decline.

Teratogen

An agent that causes congenital malformations during embryonic or fetal development; high intakes of preformed vitamin A during pregnancy act as a teratogen, causing defects like spina bifida and cleft palate.

Retinol Activity Equivalents (RAE)

The standard unit of measure for vitamin A activity; $1\,\mu\text{g}$ of retinol equals $1\text{ RAE}$, which is also provided by $12\,\mu\text{g}$ of dietary beta-carotene.

Xanthophylls

Red and yellow pigments found in vegetables such as beets and corn that do not exhibit vitamin A activity in the body.

Calciferol

The general term for vitamin D, a fat-soluble nutrient that the body can synthesize with the aid of sunlight from a precursor made from cholesterol.

Vitamin $D_2$

The form of vitamin D derived primarily from plant foods in the diet.

Vitamin $D_3$ (Calciol)

The form of vitamin D derived from animal foods in the diet and synthesized in human skin from 7-dehydrocholesterol via ultraviolet light from the sun and body heat.

7-Dehydrocholesterol

A provitamin compound synthesized in the liver from cholesterol and located in the skin that converts to previtamin $D_3$ upon exposure to ultraviolet sunlight.

Calcidiol

The intermediate form of vitamin D produced in the liver via the hydroxylation of vitamin $D_3$ (calciol).

Calcitriol

The fully active hormone form of vitamin D produced in the kidneys by a second hydroxylation reaction acting on calcidiol.

Calbindin

A specialized calcium-binding transport protein whose synthesis slows during vitamin D deficiency, hindering the absorption of calcium.

Rickets

A pediatric vitamin D deficiency disease characterized by failure of bones to calcify normally, resulting in growth impairments and skeletal abnormalities.

Osteomalacia

An adult condition caused by vitamin D deficiency marked by poor bone mineralization that makes bones painful, soft, flexible, brittle, and deformed.

Osteoporosis

A skeletal condition characterized by reduced bone density and loss of calcium from the bones, resulting in an increased susceptibility to fractures.

Alpha-Tocopherol

The only subgroup member among the tocopherols and tocotrienols recognized to satisfy the ongoing nutritional vitamin E requirements of the human body.

Erythrocyte Hemolysis

The rupture of red blood cell membranes caused by the oxidation of polyunsaturated fatty acids, serving as a classic sign of vitamin E deficiency.

Prothrombin

An inactive protein precursor synthesized with the participation of vitamin K that is enzymatically converted to thrombin during the blood-clotting cascade.

Thrombin

An active enzyme formed from prothrombin that converts the soluble blood protein fibrinogen into insoluble fibrin strands.

Fibrin

An insoluble protein meshwork formed from fibrinogen by thrombin that traps blood cells to form a clot and stop bleeding.

Osteocalcin

A calcium-binding bone protein activated by vitamin K that assists in reducing bone turnover and protecting against fractures.

Phylloquinone

The naturally occurring dietary form of vitamin K (also called vitamin $K_1$) predominantly present in leafy green vegetables and certain plant oils.

Menaquinone

The form of vitamin K (also called vitamin $K_2$) synthesized by bacteria living in the human gastrointestinal tract.

Free Radical

An unstable, highly reactive molecule possessing one or more unpaired electrons that can cause cell damage by oxidizing polyunsaturated fatty acids, DNA, RNA, and proteins.

Antioxidant

A dietary compound capable of neutralizing free radicals by donating an electron, thereby defending cellular components against oxidative stress and damage.