Glossary of Terms & Definitions
Listed Alphabetically - "H"

Haldane effect: In the presence of oxygen, less carbon dioxide binds in the blood because when oxygen combines with hemoglobin, the hemoglobin becomes a stronger acid, which combines with less carbon dioxide.

Haploid: Having half the number of chromosomes characteristically found in the somatic cells of an organism; characteristic of mature gametes.

Hartnup's disease: a genetic disorder resulting in defective absorption of the amino acid, tryptophan.

HDL: high density lipoproteins. HDL transport cholesterol from the tissues to the liver where it can be eliminated in bile. HDL-cholesterol is considered good cholesterol, because higher blood levels of HDL-cholesterol are associated with lower risk of heart disease.

Heme: compounds of iron complexed in a characteristic ring structure known as a porphyrin ring.

Hemodialysis: a medical procedure that uses a specialized machine to filter waste products from the blood, while restoring its normal constituents. Hemodialysis is needed to perform the work of the kidneys if they can no longer function effectively.

Hemoglobin: the oxygen-carrying pigment in red blood cells.

Hemolysis: rupture of red blood cells.

Hemolytic anemia: Anemia resulting from hemolysis (the rupture of red blood cells).

Hemorrhage: excessive or uncontrolled bleeding.

Hepatic: Refers to the liver.

Hepatitis: literally, inflammation of the liver. Hepatitis caused by a virus is known as viral hepatitis. Other causes of hepatitis include toxic chemicals and alcohol abuse.

Hereditary spherocytosis: a hereditary form of anemia characterized by abnormally shaped red blood cells which are spherical and abnormally fragile. The increased fragility of these red blood cells leads to hemolytic anemia (anemia caused by the rupture of red blood cells).

Heterodimer: a dimer or complex of two different molecules, usually proteins.

Heterozygous: possessing two different forms (alleles) of a specific gene.

HIV: human immunodeficiency virus. The virus that causes AIDS.

Homocysteine: a sulfur-containing amino acid, which is an intermediate in the metabolism of another sulfur-containing amino acid, methionine.  Elevated homocysteine levels in the blood have been associated with increased risk of cardiovascular disease.

Homodimer: a dimer or complex of two of the same molecule, usually a protein.

Homologous: having the same relative position, value, or structure.

Homozygous: possessing two identical forms (alleles) of a specific gene.

Hormone: a chemical secretion released by a gland or a tissue, which affects or regulates the activity of specific cells or organs.  Complex bodily functions, such as growth and sexual development, are regulated by hormones.

Human growth hormone (HGH): Hormones secreted by the anterior pituitary gland that stimulates growth of body tissues, especially skeletal and muscular tissues.  Also known as somatotropin and somatotropic hormone (STH).

Huperzine-A: (Main function: acetylcholine esterase inhibitor) (Pronunciation: hoo-PEHR-zeen). Huperzine is an alkaloid found in the club moss, Huperzia serrata – a plant used in Chinese traditional medicine. Huperzine is a potent inhibitor of the enzyme that disposes of acetylcholine in the brain; it therefore elevates acetylcholine levels. When taken orally, huperzine has shown a high bioavailability and rapid penetration into the brain. Side effects are minimal at therapeutic doses. Huperzine exhibits memory-enhancing activities in animals and humans. Its benefits are said to include increased alertness, greater short-term memory retention and increased energy. Huperzine shows promise for treating Alzheimer’s disease and other dementias because: It reduces oxidative damage produced by beta-ameloid protein (a protein overproduced in Alzheimer’s brains); It elevates acetylcholine levels that are typically depleted by Alzheimer’s; It has demonstrated ability to enhance memory; It has a longer duration of action and higher therapeutic index than tacrine and donepezil (the best FDA-approved Alzheimer’s drugs). Read more...

Hydroxyapatite: a calcium phosphate salt. Hydroxyapatite is the main mineral component of bone of bone and teeth, and is what gives them their rigidity.

Hydroxylation: a chemical reaction involving the addition of a hydroxyl (-OH) group to a compound.

Hyperparathyroidism: excess secretion of parathyroid hormone by the parathyroid glands resulting in the disturbance of calcium metabolism. Symptoms may include increased blood levels of calcium (hypercalcemia), decreased blood levels of phosphorus, loss of calcium from bone, and kidney stone formation.

Hypertension: high blood pressure, defined as a systolic blood pressure greater than 140 mm Hg and/or diastolic blood pressure greater than 90 mm Hg. 

Hyperthyroidism: an excess of thyroid hormone which may result from an overactive thyroid gland or nodule, or from taking too much thyroid hormone.

Hypoparathyroidism: a deficiency of parathyroid hormone, which may be characterized by low blood calcium levels (hypocalcemia).

Hypothalamus: An area at the base of the brain that regulatesbodily functions, such as body temperature, hunger, and thirst.

Hypothesis: an educated guess or proposition that is advanced as a basis for further investigation. A hypothesis must be subjected to an experimental test to determine its validity.

Hypothyroidism: a deficiency of thyroid hormone which is normally made by the thyroid gland, located in the front of the neck.