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

A comprehensive vocabulary review of fat-soluble vitamins (A, D, E, and K), covering metabolic conversions, active chemical forms, physiological roles, and deficiency disorders.

Retinoids

The collective term for the three chemically active forms of vitamin A in the body: retinol, retinal, and retinoic acid.

Retinol

The alcohol form of vitamin A that supports reproduction and serves as the primary transport and storage form in the body.

Retinal

The aldehyde form of vitamin A that participates in vision and forms the photosensitive pigment rhodopsin.

Retinoic acid

The acid form of vitamin A that acts like a hormone to regulate cell differentiation, growth, and embryonic development.

Beta-carotene

A plant carotenoid and precursor to vitamin A that can be cleaved into retinal in the intestine and liver; acts as an antioxidant protecting against disease ($12\,\mu\text{g}$ of beta-carotene is equivalent to $1\,\mu\text{g}$ of vitamin A).

Rhodopsin

A light-sensitive pigment found in the photosensitive cells of the retina that contains retinal and opsin, essential for converting light energy into nerve impulses.

Goblet cells

Specialized epithelial cells in the mucous membranes lining internal body surfaces that synthesize and secrete mucus.

Keratinization

The process occurring in vitamin A deficiency where epithelial cells change shape and secrete the hard protein keratin instead of maintaining normal mucus-producing function.

Follicular hyperkeratosis

The accumulation of keratin around hair follicles, resulting in dry, rough, and bumpy skin due to vitamin A deficiency.

7-dehydrocholesterol

A precursor made in the liver from cholesterol that resides in the skin and is transformed into previtamin $D_3$ upon exposure to ultraviolet light from the sun.

Calciol (Vitamin $D_3$)

The inactive vitamin D compound formed in the skin from previtamin $D_3$ via body heat, or absorbed directly from animal food sources.

Calcidiol

The form of vitamin D produced in the liver through the first hydroxylation reaction of vitamin $D_3$ (calciol).

Calcitriol

The fully active hormonal form of vitamin D produced in the kidneys via hydroxylation of calcidiol, which regulates calcium and phosphate concentrations.

Calbindin

A calcium-binding transport protein in intestinal cells whose synthesis slows during vitamin D deficiency, resulting in impaired calcium absorption.

Rickets

The vitamin D deficiency disease in children characterized by inadequate bone mineralization, failure of bones to calcify normally, and skeletal deformities like bowed legs.

Alpha-tocopherol

The only member of the tocopherol and tocotrienol vitamin E subgroups that is actively maintained in human plasma and meets the body's nutritional requirements.

Prothrombin

A precursor protein synthesized by the liver that requires vitamin K for activation into the enzyme thrombin during the blood clotting cascade.

Osteocalcin

A calcium-binding protein produced by osteoblasts that requires vitamin K to bind bone-building minerals; deficiency results in lower bone mineral density.

Thrombus

A blood clot composed of platelets, fibrin strands, and red blood cells that obstructs normal vascular blood flow.