Medical Dictionary Definitions A-Z List
Medical Dictionary Definitions A - Z - «H»:
Helix, double: The structure of DNA with the two strands of DNA spiraling about one other.
The double helix looks something like an immensely long ladder twisted into a helix, or coil. The sides of the "ladder" are formed by a backbone of sugar and phosphate molecules, and the "rungs" consist of nu...
HELLP syndrome: A syndrome featuring a combination of "H"
for hemolysis (the breakdown of red blood cells), "EL" for elevated liver
enzymes, and "LP" for low platelet count (an essential blood clotting
The HELLP syndrome is a recognized complication of preeclampsia
and eclampsia (toxe...
Helmet, bicycle: A well-known but often neglected device designed to protect the head of a bicyclist.
Helmets decrease the risk of head injuries (traumatic brain damage) by about 85%. Unfortunately, only about 18% of bicyclists in the US use helmets all or most of the time. Universal helmet use coul...
Helminth: A worm classified as a parasite. (A parasite is a disease-causing organism that lives on or in a human or another animal and derives its nourishment from its host.) Lice are examples of parasites that live on humans; bacteria and viruses are examples of parasites that live either on humans...
Helminthology, medical: See: Medical helminthology....
Helminthphobia: An abnormal and persistent fear of being infested with parasitic worms called helminths. The eggs of these worms can contaminate air and water, particularly where hygiene is poor. They can also contaminate foods such as pork and beef as well as pets and wild animals, objects such as ...
Helper cell: A type of T cell that participates in the immune response by recognizing foreign antigens and secreting substances called cytokines that activate T and B cells. Helper cells fall into two main classes: those that activate other T cells to achieve cellular inflammatory responses; and tho...
Hem-onc: Short for Hematology-oncology....
Hemangioma: A birth irregularity where a localized
grows rich in small blood vessels. Capillary hemangiomas are composed
nearly entirely of
tiny capillary vessels. Cavernous hemangiomas are composed of blood-
"lakes" and channels. An hemangioma may be visible
Hemangioma, capillary: A type of hemangioma (a benign tumor formed by a collection of excess blood vessels) that is composed almost entirely of tiny capillary vessels.
Capillary hemangiomas may be located anywhere on the body but they are most common on the face, scalp, back, and chest. They may b...
Hemangioma, cavernous: A type of hemangioma composed of blood-filled "lakes" and channels. It is typically raised and red or purplish.
A cavernous hemangioma may diminish in size following trauma, bleeding or ulceration but it rarely disappears on its own. Small cavernous hemangiomas sit...
Hemangioma, hepatic: A common benign tumor of the liver made up of small blood vessels. Hepatic hemangioma is the most common benign liver tumor and is 4-6 times more common in women than men (female hormones may promote its formation and growth).
These tumors are usually small, a quarter inch (less...
Hemarthrosis: Blood in a joint. ...
Hematemesis: The medical term for bloody vomitus.
"hematemesis" is made up of "hema-", blood + "emesis", vomit = bloody
Hematochezia: Bright red blood in the stool, usually from the lower gastrointestinal tract -- the colon or rectum -- or from hemorrhoids.
The term "hematochezia" is rarely used. "Bright red blood in the stool" is more widely used (and understood)....