Chapter 9: Vitamin Overview and Fat-Soluble Vitamins

Vocabulary practice flashcards focusing on the classification, chemical forms, metabolic functions, dietary sources, and deficiency disorders of vitamins and fat-soluble vitamins (A, D, E, and K).

Vitamin

A complex organic compound that regulates certain metabolic processes, cannot be synthesized by the body in amounts sufficient to maintain health, and results in a deficiency disorder that can be cured if resupplied in time.

Bioavailability

The extent to which the digestive tract absorbs a nutrient and how well the body uses it.

Fat-Soluble Vitamins

Hydrophobic vitamins ($A$, $D$, $E$, and $K$) found in lipid portions of food that require dietary fats and lipoproteins for absorption and transport, and are stored primarily in the liver and adipose tissue.

Water-Soluble Vitamins

Hydrophilic vitamins (the $B$ vitamins and vitamin $C$) that dissolve in watery components of the body, are absorbed directly into the bloodstream, are minimally stored (with the exception of vitamin $B\text{-}12$), and have excess amounts excreted in urine through the kidneys.

Free Radical

A highly reactive and unstable chemical substance containing an unpaired electron, generated from oxidation reactions, that can remove electrons from stable molecules and trigger destructive chain reactions.

Antioxidant

A substance that protects cells by donating electrons to free radicals, thereby neutralizing them without becoming unstable.

Preformed Vitamin A (Retinoids)

The biologically active forms of vitamin $A$ (retinol, retinal, and retinoic acid) found exclusively in animal food products and fortified foods that are absorbed more efficiently than plant carotenoids.

Carotenoids

Plant pigments that function as phytochemicals and antioxidants, some of which act as provitamin $A$ precursors ($\beta$-carotene, $\alpha$-carotene, and $\beta$-cryptoxanthin) that can be converted into vitamin $A$ by the body.

Rhodopsin

A light-sensitive visual pigment located in the rod cells of the retina, formed by the binding of retinal to the protein opsin, that enables vision under low-light or dim conditions.

Night Blindness

An early sign of vitamin $A$ deficiency marked by the impaired ability of the eyes to adjust and maintain vision in dim light.

Macula

The central area of the retina responsible for detailed central vision, which contains high concentrations of the carotenoids lutein and zeaxanthin that impart a yellow color.

Carotenemia

A harmless condition resulting from high dietary intakes of carotenoids where excess pigment accumulates, causing the skin to temporarily turn a slight yellow-orange color.

Xerophthalmia

A severe eye condition caused by vitamin $A$ deficiency resulting from keratin buildup, corneal damage, and abnormal dryness that progresses to Bitot's spots and permanent blindness.

$$7\text{-Dehydrocholesterol}$$

A provitamin precursor found in human skin that is converted into vitamin $D_3$ (cholecalciferol) upon exposure to ultraviolet light ($\text{UVB}$).

Ergocalciferol (Vitamin $D_2$)

The chemical form of vitamin $D$ found in plant food sources, such as mushrooms and yeast exposed to ultraviolet light.

Cholecalciferol (Vitamin $D_3$)

The form of vitamin $D$ found in animal food sources and synthesized endogenously in the skin from $7\text{-dehydrocholesterol}$.

Calcidiol ($25\text{-Hydroxyvitamin } D$)

The inactive circulating form of vitamin $D$ synthesized in the liver from cholecalciferol.

Calcitriol ($1,25\text{-Dihydroxyvitamin } D$)

The most biologically active hormonal form of vitamin $D$, synthesized in the kidneys from calcidiol, which stimulates calcium and phosphorus absorption in the intestine.

Parathyroid Hormone (PTH)

A hormone secreted by the parathyroid glands when blood calcium falls below normal, acting to stimulate kidney calcitriol activation, increase intestinal calcium absorption, reduce urinary calcium excretion, and promote calcium removal from bone.

Rickets

A bone disorder in children caused by vitamin $D$ deficiency characterized by improper bone mineralization, leading to soft, weak, and malformed bones such as bowed legs.

Osteomalacia

A condition in adults characterized by softening of the bones and defective bone mineralization resulting from inadequate vitamin $D$ status.

Alpha-Tocopherol

The major biologically active form of vitamin $E$ utilized by the human body and found in dietary supplements, vegetable oils, nuts, and seeds.

Phylloquinone (Vitamin $K_1$)

The form of vitamin $K$ synthesized by plants, found predominantly in green leafy vegetables such as kale, spinach, and broccoli.

Menaquinone (Vitamin $K_2$)

The form of vitamin $K$ found in animal and fermented foods, and synthesized by commensal bacteria in the large intestine.

Prothrombin

An inactive blood-clotting precursor protein that requires vitamin $K$ and calcium to be converted by prothrombin activator into active thrombin.

Fibrin

An insoluble protein converted from soluble fibrinogen by thrombin that forms an interlacing mesh to trap platelets, blood cells, and fluid to establish a blood clot.