Vitamin D Council Glossary

S-adenosyl-L-methionine (SAMe)

A direct metabolite of the essential amino acid L-methionine and the methyl-group donor in the biosynthesis of DNA and RNA, phospholipids, proteins, epinephrine, melatonin, creatine, and other molecules.

S-phase

Cell-cycle period during which DNA replication takes place.

Sclera

The white, protective outer layer of the eye.

Seasonal Affective Disorder (SAD)

Winter depression that is caused by decreased sunlight and is more prevalent at higher latitudes. Symptoms include feelings of depression, lethargy, fatigue, cravings for sweets and starches, headaches, sleep problems, and irritability.

Secondary hyperparathyroidism (Hyperparathyroidism)

Excessive parathyroid hormone (PTH) secretion in response to hypocalcemia due to a pre-existing condition, usually chronic renal failure.

Secosteroid

A molecule that is similar in structure to a steroid, except two of its four B-ring carbon atoms (C9 and 10) are un-joined. Vitamin D is the most important secosteroid in the human body.

Sequential multi-channel analysis (SMA)

Group of chemical tests performed on serum (the portion of blood without cells) to measure the levels of chemical substances released from various tissues in the body.

Serotonin (5-hydroxytryptamine)

Hormone in the pineal gland, digestive tract, brain, and blood platelets. Serotonin acts both as a chemical messenger that transmits nerve signals between nerve cells and that causes blood vessels to narrow. Changes in serotonin levels in the brain can alter mood.

Silicosis

Deadly collagenous and inflammatory pneumoconiosis caused from inhaling sand dust.

Single nucleotide polymorphism (SNP)

A variation of a single nucleotide of DNA useful in understanding and identifying a higher risk of a disease in particular people.

Sitocalciferol (Vitamin D5)

Vitamin D analog produced by irradiating 7-dehydrositosterol.

Somatic Nervous System (SNS)

Includes all nerves controlling the muscular system and external sensory receptors.

Spectrum Disorder

Group of disorders with similar features where one person may exhibit mild symptoms while another has more severe symptoms.

ST segment

The period from the end of ventricular depolarization to the beginning of ventricular repolarization on an Electrocardiogram. If elevated or depressed, can be a sign of ischemia and hyperkalemia.

Steroid hormone

Steroid that acts as a hormone by binding to and activating receptor molecules that serve to regulate gene expression.

Steroid hormone receptor

Intracellular receptor that performs signal transduction for steroid hormones and is part of the nuclear receptor family.

Sterol

Steroid that provides important signals and metabolic communications. Vitamin D derivatives are sterols.

Substrate

Molecule which is acted upon by an enzyme.

Substrate inhibition

Inhibition of an enzyme activity by a substrate of the reaction catalyzed by that enzyme.