Dictionary

holandric inheritance Inheritance of genes on the Y chromosome. Because only males normally have Y chromosomes, Y-linked genes can only be transmitted from father to son.

hole, macular See macular hole.

Holter monitor A type of portable heart monitor that is a small electrocardiogram (EKG) device worn in a pouch around the neck or waist. A Holter monitor keeps a record of the heart rhythm, typically over a 24-hour period, and the patient keeps a diary of activities and symptoms. The EKG recording is then correlated…

homeobox gene A gene containing a short DNA sequence of about 180 base pairs referred to as a homeobox. Homeobox genes encode proteins that bind and regulate the expression of DNA in multicellular organisms. Homeoboxes are present in the genomes of many organisms from fruit flies to humans, and they appear to determine when particular…

homeopath A person who practices homeopathy.

homeopathy Founded in the 19th century, a practice that is based on the concept that disease can be treated with minute doses of drugs thought capable of producing in healthy people the same symptoms as those of the disease being treated. This principle is similar to the concept behind exposure therapy for allergies, but the…

homo- Prefix meaning same, as in homology (similarity in DNA or protein sequences between individuals or between species) and homosexual (a person who is sexually attracted to persons of the same sex). The opposite of homo- is hetero-.

hippocampus An area deep in the forebrain that helps regulate emotion, learning, and memory.

Hippocratic Oath An oath taken by new physicians authored by Hippocrates. The oath represents a promise to act ethically: to treat the ill to the best of one’s ability, to preserve a patient’s privacy, to teach the secrets of medicine to the next generation, and so on. See also Daily Prayer of a Physician.

Hirschsprung’s disease An abnormal condition that is present at birth and is due to absence of the normal nerves (ganglia) in the bowel wall. Nerves can be missing starting at the anus and extending up a variable distance of the bowel. This results in enlargement of the bowel above the point of the missing nerve,…

hirsute Having an overabundance of hair.

hirsutism Having excessive facial and bodily hair. Hirsutism can be a side effect of certain medications (such as prednisone) or reflect an underlying hormonal imbalance.